Inexpensive Silicone Molds w/ RTV?

[rickb]

Hello out there.

If anyone has experience or information using using silicone RTV from tubes (like from Home Depot) to make molds I'd appreciate hearing it. I'm especially interested in drawbacks that may not be obvious -- like shrinkage, aging, strength, etc.

In Philadelphia this summer, I met some sculptors who used 100% Silicone rubber caulking (thinned with xylene if required) as a cheaper alternative to other specialty mold-making silicones (like Rhodia -- which is >$100/gallon).

I just tested it on a few small samples (oil-based clay). Besides taking days to cure, it's pretty convenient (no precision mixing or degassing), seems to pick up detail OK, and required no mold release.

Am I missing something? Or if I can tolerate the long cure time is this a good alternative at about 1/3 the cost?

Thank you very much,

Rick


http://www.richardbecker.com

[fritchie]

Hello out there.

If anyone has experience or information using using silicone RTV from tubes (like from Home Depot) to make molds I'd appreciate hearing it. I'm especially interested in drawbacks that may not be obvious -- like shrinkage, aging, strength, etc.

....... etc.

Am I missing something? Or if I can tolerate the long cure time is this a good alternative at about 1/3 the cost?

Thank you very much,

Rick





On the suggestion of a local sculptor just beginning his own foundry, who cast a couple of early pieces for me, I used something like that to cast in plaster an oil-clay figure a young friend did, for his mother. This guy said these molds were OK for maybe a couple of casts. I found detail good. My material set up quickly, but was quite thin. Maybe that’s the difference between what I did and what you did.

I made a plaster mother mold and had no trouble, except that it would have been easier to have a thicker rubber.

[lowpoly]

As this type of silicone uses air humidity to cure, you can always stir a few drops of water in to shorten the cure time. Some people use acrylic paint (?) as a catalyst because it gives a visual feedback about the mixture.

[rickb]

Guys, Thanks for the tips. I will definitely try the water catalyst. Any idea how much water -- you mentioned a few drops -- is that per tube? If you dont know, I'll test it out -- anything to speed it up would be worth trying.

[lowpoly]

No, that's for less than a tube. You probably have to test it out.

[Toby]

Been trawling web for similar received wisdom.
www.taxidermy.net/forums/MoldingMenu.html suggests a few drops of glycerine, distilled water, 'bondo' cure accellerator (presumably polyester resin brandname?) and some particularly exotic chemicals which would probably lead to phonetapping from the CIA.
So today I'm off to try clear silicone and glycerine + some acrylic paint indicator. If anyone has noticed a runaway chemical reaction, steaming puddles of ex-oil-clay or other drawbacks with this, write quick.
Heres the next thing for the ingenious collected wisdom out there: easy mold (mould) cases. Plaster bandage is good, but tends to disintegrate. Wooden shuttering works, but requires gallons of moulding compound to fill it for anything notably 3-dimensional. Fibreglass looks good but pricier/stinkier.
How about expanding urethane foam-in-a-can, squirt on, let dry and poof! insta-mold-case. One thing I like about this is its lightness.. I make lost wax shells inside moulds and consequently have to tip the moulds in all directions. On some of the larger hemp-reinforced plaster mould cases this has been a herculanean task.
Has anyone tried this?? or miles of duck tape and cardboard? Has anyone finished a gargantuan moulding project and then thought "Gee, I'd have done this in an afternoon if I'd only used ...". All the professional mouldmakers I have met seem to produce beautiful intricate interlocking moulds using very traditional materials; do they all share some dark secret, that they can achieve the same results with toilet paper and diluted PVA glue?

[fritchie]

Re: Inexpensive Silicone Molds w/ RTV?; making waxes
Toby - This is more to the point of getting your waxes than getting the mold itself, but here are two simplifications I've either used or seen. If the mold isn’t too big (I’ve done full figures, but on about 2/3 lifesize scale), you can fill the whole, assembled mold and pour out most of the wax after letting it cool for the right amount of time.

I usually get the wax just above its melting point, when it starts to form a “skin” in the melting pot, and let it sit in the mold for maybe 2 - 3 minutes. You can shift the mold a bit and watch wax buildup at the top, to gauge thickness. I’ve had great success this way, though you may have to paint in extra wax at sharp projections such as armpits and so on. Sometimes this can be done simply by pouring coolish, fluid wax into the complete mold and rotating properly; sometimes by reaching in by hand or with a long, bent wire with a bit of rag attached at the end.

Alternatively, you can paint fluid wax into each mold section, to the proper thickness, assemble the mold, and pour a little warm wax into each joint. This is more problematic, but my founder prefers this method, and I have used it. I seem to get more bubbles on the surface this way, and more surface finish work, but that’s probably a matter of technique.

Also, I have suspended heavier molds flexibly at midpoint over a wax pot when using the pour method, so I can fill the mold, manipulate it a bit, and then empty it at the right time.

[pinballannie]

Hello out there.

If anyone has experience or information using using silicone RTV from tubes (like from Home Depot) to make molds I'd appreciate hearing it. I'm especially interested in drawbacks that may not be obvious -- like shrinkage, aging, strength, etc.


http://www.richardbecker.com

Hi RickB:
I've used RTV as well as eurethanes and silicones, and the RTV works pretty well for a limited set of parameters.

As you probably discovered, it takes forever to cure, and if it's on too thick, it only cures on the outside and will leave pockets of uncured RTV in the middle for A VERY long time that you discover at very inopportune times. In my experience anyway. Worth it to put on multiple layers over time to build it up--really easy to use plastic wrap as a barrier to smooth in on over large surfaces and work out the bubbles that seem to collect in concave areas. I have also used layers of saran wrap in between layers of RTV to give it more strength, but sometimes it pulls apart oddly when you cut the mold off.

I've used it mostly for pretty small things, and have jeweler friends who use it for their solid wax forms on that scale.

I've wondered about a thinning agent...haven't heard of the xylene before. I also like that it's clear (I tend to use the tub/tile stuff that's a milky clear color because you can see the underlying form a bit) and that it's so flexible.

Downsides, aside from the cure time, is that it rips really easily, and degrades pretty quickly...less on a chemical level than a structural level.

I have also tried casting with it into open face molds to capitalize on that milky pink/white color, which is pretty interesting, and it came out surprisingly well...though that's when I was looking for the thinning agent to deal with it not filling small corners of the mold--too stiff.

I've had it with eurethanes so I do go back to RTV when a project doesn't seem worthy of the expense of silicone. I make a lot of molds of fruit/pods which are often moist, so the moisture cure is great.

Best of luck, and thanks for the xylene tip.

PBAnnie

[Toby]

Thanx fritchie for wax tips.. I find the heavier the case is, the less comfortable I am suspending it from one point.
Pinballannie! Did you ever modify the content of the moisture-cure builder silicone? Add accellerators? How thick were you applying it? How long did it take to dry?

[pinballannie]

Toby!
Ummmm...never used accelerators, as in accelerating set time/consistency like a thixotropic?...curious though so please share if you have tidbits.

I have never had much luck applying layers thicker than 1/8" (sorry, don't know metric conversion offhand) and letting them dry at least a couple of days between coats. I usually gingerly sniff to see if it feels like the RTV has stopped gassing off...that usually seems like a pretty good indicator, though not for huffing! I'm not quite sure how toxic the gases are. Do you know?

The RTV also affects the positive chemically, so if they are vegetables/pods in my case, it essentially rots them so when you cut it off it's pretty disgusting. Not that it's a concern for everyone. :)

PBAnnie

[Toby]

Followed taxidermist advice. Mixed 4 to 5 drops glycerine + dash of acrylic paint into clear bog-standard builder silicone (1 oz/28g). Paint gives good indication of homogenity. Wear mask, eyewatering vinegar pong (you've probably been there).
Applied to a clay model with a butterknife. Marvellous. Tendency to entrap bubbles; spread thin initial coat myself. 20 mins working time. Applied to 3/4" deep in places (could have been thicker if desired). No need to make more sticky or viscous. Can be applied upside-down.

This leads on to next experiment. (Of course I should reduce the number of variables/experiments per piece but that's why I left engineering)
Expanding-foam-in-a-can mould cases.
Works. Difficult to control depth and even-ness. Impossible to work while wet.
Tends to run off sloped surfaces.. blop.. , don't bother trying to pick up again.
Pretty much lost track of mould seam fence (rows of pins supporting vaselined masking tape) Currently re-excavating. Does'nt stick well to itself once dried :mad:
May work best with deep shim fences. Pricier than plaster bandage. Good rigidity + flexibility combination. Bit toxic (isocyanide foaming agent: read cyanide). There is future for this stuff but I think I'll stick to plaster bandage for the next one.

[Toby]

Two points from re-reading above:
Distinction between Urethanes and Room Temperature Vulcanising Silicones.
Two totally different groups of plastics. Here I differentiate between

A: Mold-makers 2 part RTV silicone and
B: Builders 1 part RTV silicone

Two quite similar plastics, one being pricier but having a different cure mechanism.
As far as I know, the odour (odor in imperial) is that of acetic acid, which is the main component in vinegar. This is the evil stink released by one of the catalysts in builders silicone sealant. I don't know if it's toxic or merely unpleasant (akin to sauerkraut sauna)

[Louie Arce]

The idea of using water to accelorate the tube caulking from Home Dept is on the correct path. I will expand on that idea. Take a five gallon bucket , fill it with water and squirt the silicone tube in the bucket. Kneed the silicone with hands and it will ball up into one mass. This proccess is washing out the chemical used in the silicone that retards the drying proccess. In about an hour or so the silicone will set up(cure). Before it sets it can be pushed and molded over the form like an RTV rubber. When you have the desired thickness make a mother mold from paster for the mold support. I have seen this used for bust size sculpture with great detail....good luck. Post results for others to see...thanks Louie

[Toby]

I've been using a trick gleaned from a taxidermist website.
Clear builders silicone + 6 drips glycerine + teeny smear of acrylic paint.
Hold nose and mix thoroughly with butterknife.. nearest implement. Slap onto model, build up thick layer and slap a plaster bandage case around it.
Acetic acid (vinegar) fumes released, pongy but I appear to have survived. Problems can be trapped bubbles near surface. I;m using this method in a taught course where administration would throw a wobbly if I billed them for 2-part silicone.
Glycerine: available in chemists, drug-stores.. used for cake icing and nitroglycerine.

[Toby]

Read 3 squirts silicone + 6 drips glycerine + smear of arcylic paint (used to indicate thorough mixing). Squirt = caulk applicator gun trigger full squeeze. Yes, english is my first language, mbung

[Landseer]

I think people pretty answered the issues on this, I know from using silicone caulk that it can skin over and stay liquid inside a thick section for a long time. The stuff also tends to be VERY stiff like tire rubber almost, and it tends to break. I used the 50 year silicone caulk on an RV roof in the seams- one tube per seam.
It lasted well, but when I junked the RV and salvaged the aluminum sheets off the roof, I noticed I could break or tear the silicone as well as scrape it off. It was still pliable etc just that when "bent" over at a good angle it "broke" and left chunks on both sides.

I suspect if you examine the idea of caulk in depth, first ask yourself this question because it answers it for you:

"If this works good and is cheap, then how come EVERYONE isn't using it for molds instead of $100+ a gallon mold rubber you have to order and ship?"
I think the answer becomes obvious right there.

[Toby]

It sets because of exposure to atmospheric moisture.
Thats why deep sections never fully set.

This is why glycerine is mixed through it, so that it sets fully in deep sections, the acrylic is to check if it has been thoroughly mixed.
2 part is better for avoiding bubbles (if depressurised) and is less viscous.

You don't believe me? Go try it

[clifton]

well, dunno if I should weigh in on this
after all, I'm no expert
but ...
I have been using the clear silicone for making molds
(the 30 year kind)
for about three years, now
I get it on special at the local hardware store
3 tubes for 9.99

apply it in thin (up to 1/4" thick) layers
reinforce with drywall mesh where needed
never used any additives
just straight from the tibe

hardest part was getting it to release from the carving
a release agent made by mixing vaseline and camp fuel, or naptha fuel
did the trick
commercial ones didn't seem to work

the silicone is harder to work because it's quite thick
but the clear allows me to see any trapped bubbles
and work them out

a mold lasts for about 30 cast cement copies
maybe not as many copies on intricate figures
the mold will eventually crack with use

it worked for cast paper, too
I'm moving over to casting in resin
a thin application of release agent is needed for that
to avoid sticking to the mold

an example of a small reproduction made this way:

"Hanging off the Traps!"

http://www.cliftonsears.com/fish/hanging_sv.jpghttp://www.cliftonsears.com/fish/hanging_bv.jpg
http://www.cliftonsears.com/fish/hanging_tv.jpg
12" long by 7" high

Clifton
_________

[Landseer]

I have been using the clear silicone for making molds
(the 30 year kind)
for about three years, now
I get it on special at the local hardware store
3 tubes for 9.99

hardest part was getting it to release from the carving

the silicone is harder to work because it's quite thick

a mold lasts for about 30 cast cement copies
maybe not as many copies on intricate figures
the mold will eventually crack with use

Seems to me I remember there was a definite difference between the clear and the caulk with white, silver etc when I use for it's intended purpose of caulking around the house.

That caulk is made to STICK, so I have no doubt release was an issue for you.
The thing is, with the QM 140 Silicone mold rubber, the only "release" I've done is a light coat of lacquer on the model, the stuff doesn't adhere to that at all, it didn't adhere at all to an unfired water clay model with a LOT of deep undercuts and all I did was one light coat of lacquer spray.
That was a drawback with urethane, you had to seal the model and then spray some release crap on over that and it was so slick and greasy that as you brush on the rubber it would start sliding around. The QM140 had no tendency to do that.

I find no matter how carefully I brush on the rubber, I always get some air bubbles trapped, and the thicker the rubber is the worse that factor becomes. So the caulk besides being really think and sticky sticks like strong vinegar, the nice thing about working with the QM140 is the base has NO smell at all, the purple catalist has a slight odor sort of like ink, certainly no fumes!

Ok so you find you get about 30 casts before the rubber cracks or otherwise deteriorates, your caulk is probably fine for what you do, especially if you only make a few casts, or just want one quick mold of a model to get one cast to refine more, and make a permanent mold of that.

I have done that many times when I need to do just that sort of thing,
but usually the materials cost ($9.99 v/s $90.00) is not as important as your TIME spent making and replacing molds.

For me, I would much rather concentrait on casting and making money from my finished casts (which are what bring sin the money not the molds) than spending time I shouldn't have to replacing cracking or deteriorating molds over and over- that's just 100% pure COST and a total loss, and the time is better spent with quality materials to start with so the molds last as long as possible.

By now I must have some 40 molds and most of them are fairly large, many took a good gallon of rubber to make, all but the recent 4 I made are polyurethane and I won't use that again, now I know offhand I have at least 3 molds that have to be replaced because the rubber was from a bad batch and maybe 3-4 that started to tear in thin areas because that rubber is not very strong.
Replacing these molds is each an all afternoon or longer affair, then besides the rubber there's the plaster shell, so two-three hundred pounds of plaster there and then having to dispose of the OLD ones is also a headache.
So you can see why in my case I would want the best material I can find regardless of the cost, because whether a mold costs me $10 or $100 is not an issue when it takes 6-8 hours of my time to set up the model, make the rubber mold, and the plaster shell when I could be casting dozens of pieces to sell in 6-8 hours, or something more productive than backtracking!
I don't know the casting life of the QM140 v/s your 30 casts, but I do have Urethane molds I've taken 100 or more casts out of and they are still fine.
Ive had a black "Tuffy" mold that was professionally made for me before I learned how to make my own more complex molds, and I remember the rubber started to deteriorate around the 20th or so cast if not before, it was getting sticky on the inside surface and leaving bits of rubber on the hydrocal casts. That mold was $400 (1978 or so) and I doubt I got more than 40 casts out of it, so that mold cost me $10 per cast and I was only selling the casts for $38.50 DELIVERED UPS.

Your caulk at $10 for the tubes, 30 casts, say less than 50 cents a cast for the mold cost, but there's your time involved which jumps that 50 cents up a fair amount! So as you can see there's more involved in this than JUST the cost of materials.

[daaub]

Anyone have experience with the acrylic and silicone mix kind of calking? Not sure of the exact title but it cost much less then the pure silicone and can be thinned with water. I tried a small amound on a piece of dried water based clay. It picked up detail nicely and did not stick without any release ussed. Not sure about the strength though, I just tested a thin layer so far.

[clifton]

True, Landseer
trying a few things at low cost is important to me
I need to know if, and what type of, reproductions might sell

and the quality of the mold does not equal that
made with professional materials
and the stuff does stink!
but it surprised me how well it worked

a water based, silicone-like, caulking would be interesting
thanks for the heads up daaub
I'll look around for it

Clifton
_________

[daaub]

More info on the acrylic / silicone calking as it says on the tube.

DAP. Alex Plus. Acrylic Latex Caulk plus Silicone. 35 year. White, Indoor / Outdoor, Paintable, Flexible, Highly Durable, Mildew Resistant, Water Clean-Up.

I just tried this stuff out on a life size sculpture of a standing figure. Mixed it with enough water to give it the consistancy smooth mashed potatoes (best comparison i could think of, hah) and painted it on thinnly with a small brush. Actually, it was just like working with the liquid latex stuff. Took three tubes to cover the whole figure around 1/16" to 1/8" thick in areas. I hope this stuff will stick to itself when I add more layers. Never tested that! Some thinner areas were drying very quickly and I added more on top as I finished the figure and it seemed to bond well.
Never tested it on moist clay yet either, so I hope this works out.

Ohh, didn't post the price, which is what this is all about, a cheap alternative to the expensive mold making products. At Canadian Tire, it comes in a 4 tube package for $6.99 so it is about $1.75 a tube. Not bad if it works.

[clifton]

"I just tried this stuff out on a life size sculpture of a standing figure."
Daab

-------

Well, I was thinking of something more the size of a little finger, to try it on ... get a feel for how it works. I guess I'm getting old and cautious.

You have jumped in with both feet. A life size mold is a lot of work. I hope everything comes together well for you. The bonding of the caulk to itself should not be a problem.
good luck and let us know how you make out.

Clifton
________

[clifton]

Hi Daab,

I have been working with the different mixtures.
Subjective results as follows.

I found the mold made from the acrylic silicone mix that you used (I picked some up at Canadian Tire) tore very easily compared to silicone, and the mold is not as flexible. It is wonderfull stuff to use.
Easily thinned, brush it on, no odour, captures detail well with no bubbles. Great that way, but I don't think I could use it except for where I only want to make one or two casts.

I tried washing the silicone out in water and was surprised at how well it worked. The silicone set up a little too quickly but this was probably due to overwashing. One thing that I hadn't counted on was the way it stuck to my hands! I guess it would required gloves that are coated with vaseline or something. The problem I find with this method is that the silicone gets thicker, and it is already plenty thick to work with, just as it comes from the tube. Pressing it to the model and stretching it in place did not appeal to me.
But it certainly set up quickly. I can see that any who used this would find it worked well with practice.

Adding the glycerine proved most interesting. There is some sort of reaction going on there. The silicone is changed to be more resiliant and seems to be more tear resistant. I haven't used it long enough to be certain, but it sure seems that way. The drop of acrylic paint does more than indicate the mix, it is, as I think Toby mentioned above, a catalyst. The setting time is much slower without the drop or two of acrylic paint.

Again my main problem is that I don't care for applying with a butter knife. I would rather just put it on directly from the tube, if it comes to that.

My next attempts involved thinning the silicone with the Xylene mentioned above. I could not find xylene directly but did find a varnish thinner that had the chemical in it. I had thinned silicone with naptha fuel before, but it weakened the finished material and it was too soft to use for molds. This material takes a little mixing but it worked well ( er, shouldn't be mixed in plastic containers ). Thin mixtures can be coated over after a couple of days.

Adding the glycerine to the thinned silicone silicone did speen up setting time, but not like it did with silicone alone. It will require an overnight set before going on to the next step. (Back to the longer set up times.) I don't use mother molds on even quite large pieces. Haven't yet done that large though. I just reinforce with cheese cloth and dry wall mesh.

I have been making molds with the stuff at the local hardware store for about 3 years now, and it is good to finally come up with a decent brush on formula. Thanks to rickb for starting this post, and to others who posted information. Hope it is of some use to others.

Clifton
________

[Tinkerbell]

Clifton please can you tell me about yr hardware shop silicone for mold making. Im in Uk thanx

[frozenimage]

Hi all,
The shortcuts and cheap materials are interesting, but I view them as a waste of time. If you have sculpted something you really care about, using professional mold rubbers is the way to go. You will save nore time, get better castings, and be able to make the casts in years to come by using good materials. Home Depot caulk is not made for sculpture molds, it is made to seal windows and doors. I prefer exothermic polyurethane mold rubbers, for casting sculpture. I don't like natural rubber either, too long to build up coats and seam lines are a bitch using it. Use the best materials available, and they will pay for themselves.

Regards,
frozenimage

[Landseer]

Hello out there.

If anyone has experience or information using using silicone RTV from tubes (like from Home Depot) to make molds I'd appreciate hearing it. I'm especially interested in drawbacks that may not be obvious -- like shrinkage, aging, strength, etc.

In Philadelphia this summer, I met some sculptors who used 100% Silicone rubber caulking (thinned with xylene if required) as a cheaper alternative to other specialty mold-making silicones (like Rhodia -- which is >$100/gallon).

Am I missing something? Or if I can tolerate the long cure time is this a good alternative at about 1/3 the cost?
I suspect if you examine the idea of caulk in depth, first ask yourself this question because it answers it for you:

"If this works good and is cheap, then how come EVERYONE isn't using it for molds instead of $100+ a gallon mold rubber you have to order and ship?"
I think the answer becomes obvious right there. I would never use window caulk for mold making! it takes far too much time to make a model and a mold just to screw it all up trying to save a few dollars on the mold. If the stuff doesn't work right, doesn't cure in some places, you are screwed, your model is ruined, the mold will be crap and every cast made form it will be crap as well and have your name on them.
Window caulk is for sealing windows, it may be made partly OF silicone but I can assure you it's NOT the same. Silicone MOLD rubber sucha s the Quantum I use has NO fumes, does not smell like vinegar, and has never once failed me in anyway, it always cures perfectly overnight or less and is ready to use.

Yes, it's $100 a gallon/10# but geez, do the math! 10# of this will make several molds or at least a couple or three larger molds as I make- so each mold made is spread over that $100, 3 molds would be about $35 each for the proper material that works right and is MADE for casting sculptures not caulking windows.

Why would you think you need to degass mold rubber? I have never degassed mold rubber in my 30 years of making molds, it is only SUGGESTED not required. As far as accurate weighing, how hard IS it to use a little battery operated kitchen gram scale and measure 2 components at a 1 to 10 ratio and stir it?

Window caulk never seemed to last very long, seems like you have to replace or recaulk every year because it either loosens, shrinks, pulls away etc.

I totally agree with frozenimage except for one item- polyurethane, the only rubber I've had a manufacturer defect in was Polytek's polyurethane and it happened TWICE- a "problem" with one of the parts they said, but I had 3 very large very expensive molds made with it and they were unuseable, their replacement kit did the same thing, their poor response to that was when I switched to Quantum silicone, it's not inhibited by anything like polyurethane is- moisture being a big one.

[frozenimage]

I have a TIP!

Go to the Polytek Mold rubber site. They are located in Easton, Pennsylvania. For my money, they make the BEST mold rubbers going. If you are smart, and dig into the site a bit, you will come to the "trial order" offer. You can purchase trial units at reduced cost and free shipping. They also give you an awesome catalog/tip booklet that is just fab for beginners. It describes and details nearly all processes.

I realise that making a good mold is a difficult process. I have had many failures, whilst LEARNING, but the one vital thing I know is that using crappy, improvised materials is a sure way to lead to failure. Loosing that piece you worked so long on....not being able to cast it well, REALLY SUCKS! If you have great materials, and a little knowledge, you will most likely produce a mold which will give you years of service. You DON'T want to spend as much time casting the piece, as it took to sculpt it. You will loose time, money, and perhaps become discouraged. Research, buy the best materials, and deploy them well. Ok, if you are just making a mold of a finial for your stairwell, one shot cast, sure, or perhaps reproducing a cool Gothic Halloween bat bas-relief from that special girl you met at the Goth bar, sure! I am just taking time on this one, because I am in an intensive mold making procedure right now. Just got in 6 gallons of rubber. Life sized figure, arms legs, plus a few other items to mold. If you have any questions, any of you are free to e-mail me, PM, I love getting messages.

Home Depot tubes WILL take an impression. But I feel they will lead to depression.....if the work you are doing is of import. Don't skimp on materials, and don't understate your price for the finished product. Profit is NOT a four letter word.

Highest regards,
Robert

[dilida]

Just to add some more info on using tube silicone. Our foundry has used it more than twenty years, with the older molds still usable. I've personaly used it 11 years. Everyday almost.

What we use is GE construction adhesive 1201. In my experience it is tougher than anything you can buy over the counter. Haven't tried it, but I've been told adding nylon netting will help prevent tearing. At our foundry, tearing the rubbers in an exception, not the rule. Don't let the rubber build up too thick in some places, right next to a thin area, this is where it will tear. Strive for an eveness thoughout. And carefully pull the rubber off. Take your time.

It stinks! But it has worked very well for us. No Releaseant is needed for oil-based clays, but we use PVA(polyvinyle alcohol) becuse we cast wax into the molds and it just makes for a nicer wax than using nothing. If I'm making a mold on wood, plaster, card board or stone, metal, hard-fired clay, Stiffened cloth, ect. I brush on paste-wax, 2 coats to be sure entire surface is covered. You don't want to use silicone on moist, water based clays if there is any sulfur content. The silicone is eaten away by the sulfur. (I can make it work, but I advise against it if you are just beginning to make molds with this product.

I rarely use xylene to thin it down, because I don't like the toxicity of it. Besides it weakens the silicone. I use it on very small detailed work, such as beads, or a extremely detailed hair. Only use xylene about once a year on average. Squeeze a bit of silicone into a cut in half pop-can, add a little of xylene, stir with the end of a paint brush till the consistancy is that of honey, then use the other end of the brush( clean soft natural bristle) to brush on the rubber. when it starts getting tacky, throw the can and brush away, and start with clean materials. Sounds wasteful, but I only use it on small sculptures, so I think three brushes are the most I've ever used. they don't have to be expensive ones. After 20 to 30 minutes, when the rubber is tacky to the touch, put a backup coat of rubber on. If you just let the xylene coat cure, it may pull away from the surface, so it is very important to get a backup coat on soon.

I use dawn dishsoap in water to keep it from sticking to my fingers, and just squeeze a bead around the bottom of the sculpture and start pressing the rubber up around the piece with my fingers, dip into dawn/water often. The first coat is very thin, you want to make sure you press out the air bubbles. I apply 3 more coats, 12 to 24 hours, in between to make sure it cures each time. I work on several sculptures at a time, waiting a day in between coats allows me to move on to another piece, and move a whole group along at the same pace. If I just concentrated on one mold, I would probably apply the layers as soon as it cures, and I do this when I'm making my own molds at home. The rubber is clear when it's thin, somewhat opaque at four layers.

I only shim an original if the artists doesn't want it harmed i.e. a wood carving). For my parting lines, seam lines, after 2 coats of rubber overall, I squeeze a small bead where I want to divide the mold, and then pinch the bead so it is a small thin "ridge". let it cure. The next step for the ridge, is too apply a small bead on each side of the first, and then pinch it together up a little higher than the first one, so it is about an inch tall, and still thin. The third application I apply a bigger bead on each side and shape it up to a ridge that is about 3/8 to 1/2 inch thick, and 3/4 to 1 inch tall. I use a key kife to cut it so the ridge has to be thick enough to accomadate the knife.

The applications process I use is:

1.Very thin 1st layer overall, press out air bubbles. very thin.
2. thicker 2nd layer, won't be very even, rubber starts building up in crevices.
3. apply first "ridge". I already have decided where that will be before I start the rubber.
4. apply the second "ridge" making it taller.
5. apply a thicker 3rd coat overall, concentrating on evening out the rubber, high spots will need a little thicker, low spots will need thinner.
6. apply last ridge making it thick enoug to cut with a key knife. This ridge is thick and generally needs a day to set, less in hot humid conditions.
7. apply the 4th coat of rubber thinnly usually just to even out the whole thing.

There are more details I suppose, but most people are using brush on 2-part silicones, so I'm not sure how many are interested in this product. The main reason we still use it is availability in our area, and just way our foundry operates. I'd be glad to share more if there is an interest.

lisa

[Landseer]

I use dawn dishsoap in water to keep it from sticking to my fingers, and just squeeze a bead around the bottom of the sculpture and start pressing the rubber up around the piece with my fingers, dip into dawn/water often.See this is another issue, this kind of stuff is NOT hand lotion! yet people will dip their fingers and hands in this stuff to apply it probably because it's too thick to brush or brushes cost money, and this stuff is absorbed into the skin like all chemicals are and you have NO idea what kind of systemic or other health risks there are with it,especially down the road from repeated or long term exposure to this stuff.

Then there's the xylene, another extremely toxic chemical solvent you don't want to be messing with all over your fingers, skin and breathing it in.

but most people are using brush on 2-part silicones, If this works good and is cheap, then how come EVERYONE isn't using it for molds instead of $100+ a gallon (10 pounds, $10 a pound) mold rubber you have to order and ship?

First do the math and calculate the $4.99 a tube or whatever it is and how many ounces you get for that price to calculate how much it costs per ounce and you'll likely find it's not as inexpensive as you thought- anytime you get something in little tubes, tubs or packages it costs more than a bulk size.
I can't imagine a foundry using this kind of stuff for molds, must be about the only one who does.
I'd do as suggested and order a trial kit from Polytek, I would get their thixotropic formula which is applied with a brush.

I use Quantum silicone, it works a litle differently in that it is mayonaise consistency right away when mixed (polytek urethane is liquid and slowly gets thicker as you work) and it stays nice and workable with acid or chip brushes for probably 45 minutes to an hour, it doesn't "skin over" or fume out noxious chemicals. I have removed molds in as few as 8-10 hours and they were ready to cast from, but 24 hours is best.
They also have two catalists I use, one is not thixo and the other is, mixed with thenon thixo it's like pancake syrup and allows brushing into fine details and deep undercuts and stays liquid to allow trapped air to escape, then after 2 hours I apply the thixo version if I used the other first. I don't always use it as the thixo generally can be brushed into all but the deepest details perfectly if you do it with care.

I love how it works, the long working time, the NO fumes, it brushes out well, it doesn't stick to my models though I give them a shot of spray lacquer anyway, plasticene I use doesn't bother it, neither does sheetrock, wood, MDF.

But hey, if all you care about is making your molds as cheap as you can no matter how much more work it may be or the end results, then go ahead and use window caulk, construction adhesive or whatever, but keep in mind the reasons EVERYONE isn't using caulk for molds if it was all that great or "cheaper"

Me, I have far more important things to spend time on than replacing crappy molds- making molds and replacing bad ones is NOT generating you any cash it's taking it OUT of your bank, the casts make you the money and the day wasted on a crappy mold is a day of production time lost and that more than negates the "savings" from the "cheaper" caulk unless your time is not worth anything?

Making molds along with packing and shipping are probably the two things I least like doing but both have to be done, so that is why I use what I feel is the best material for the mold rubber so I don't have to fart around making that mold AGAIN, and put off it's eventual replacement as long as possible.
I have two polytek urethane 74-30 molds now that have tears and cracks in them and need to be replaced and neither pulled very many casts.
They will be replaced with Quantum silicone.

Speaking of molds I have two to make this weekend, armed with 2 gallons of rubber I'm off to do that.

[Merlion]

Thanks Lisa for passing on your experience using air-dry silicone from tubes instead of the 2-part silicone. I find this part below difficult to understand. Are you able to show us pictures of this part of the process?

For my parting lines, seam lines, after 2 coats of rubber overall, I squeeze a small bead where I want to divide the mold, and then pinch the bead so it is a small thin "ridge". let it cure. The next step for the ridge, is too apply a small bead on each side of the first, and then pinch it together up a little higher than the first one, so it is about an inch tall, and still thin. The third application I apply a bigger bead on each side and shape it up to a ridge that is about 3/8 to 1/2 inch thick, and 3/4 to 1 inch tall. I use a key kife to cut it so the ridge has to be thick enough to accomadate the knife.
What do you mean by key knife?

And any good tips on the mother mold?

[Landseer]

Here's a couple of pics, the first model is shown with 450g (1 lb) of silicone applied for the detail coat, the second has about the same applied to it. This coat generally fills in all the undercuts and deep details solid which makes the mother mold much easier to build and eliminates "hangup" points.

I've since these photos applied the second coat to each- 2000g (4.4 lbs) and 1000g (2.2 lbs) respectively, in about 90 minutes I'll add a third coat to both.
The printed scale gives a clue of the size, the first is 23" square and the depth of details etc are shown in another thread.

I like to use ordinary but new pieces of sheetrock for the model to lay on, the sheetrock is nice and smooth, flat, cheap, and seals with a spray coat of lacquer with the rest. Once the mold and model are peeled off the sheetrock is tossed.

http://i23.photobucket.com/albums/b375/Randall2/elizabeth-mold.jpg





http://i23.photobucket.com/albums/b375/Randall2/WH-R-mold.jpg



And now done after the third application, it will be ready to shell in the morning and I can cast tomorrow afternoon.
I used 4,950 g of rubber- just about 11# and I forgot to mention the KIT of quantum silicone is 11#, the BASE is 10# in a gallon tub, but it comes with a 1# container of catalist, so it's actually 11# of rubber.

http://i23.photobucket.com/albums/b375/Randall2/elizabeth-mold-done.jpg

[frozenimage]

FINE looking mold, Landseer. I am interested in the product you use, stays at mayonaisse consistency? Hmmmm...
Sorry you had a problem with Polytek. I have molds I made 10 years ago that are still perfect, using Polytek rubber. I am really good about mix ratios, also with a new batch I do a test mix to make sure it is a good batch.

I use fibergalss resin and cloth for my mother molds. $35 a gallon, available at my local Advance Auto Parts Store. Going back to Landseers price costs, it works out a tad more expensive than Plaster of Paris, but is FAR lighter in weight, also stronger, and fiberglass resin does not suck oils out of your mold rubber. It is also quite FAST to work. Once you learn good resin technique, it is unlikely Plaster mother molds will ever have attraction....unless you are going for a hernia. Lay up the resin outdoor in the sun with the wind at your back, no liver problems. Latex dishwashing gloves will last a long time, for many lay-ups.

Robert

[Merlion]

Just to mention you can also think about fiberglass plaster molds. Perhaps you know what I mean. Put a layer of fiberglass mat after the first layer of plaster and next add another layer of plaster.

[Landseer]

FINE looking mold, Landseer. I am interested in the product you use, stays at mayonaisse consistency? Hmmmm...
The Quantum silicone's QM-140 base with the Blue thixotropic cat ll is what I use and have for about the last year, it was in fact highly recommended to me by a fellow HERE. I liked what he said and got a kit to try, after being used to how Polytek 74-40 thixotropic worked it worked a little differently- a much longer working time, the 74-40 would mix up liquid and then start thickening and thickening every minute while you worked till you couldn't brush it any more. In many ways it worked ike plaster but slower.
The QM 140 starts out like mayonaise and STAYS that way for 30-45 minutes before I notice it starting to get a little harder to work. SO it works a little differently but not drastically so and with this I can mix up 2500 gms in one batch and work it onto the model with an acid brush for 30-45 minutes and it's consistant, the 74-40 I had to work faster or mix smaller batches.

Sorry you had a problem with Polytek. I have molds I made 10 years ago that are still perfect, using Polytek rubber. I am really good about mix ratios, also with a new batch I do a test mix to make sure it is a good batch.
I used that for years, but even the 74-40 was too STIFF when made in thick blankets. The issue was when I HAD a problem which was obvious, their first response attitude implied it was MY fault, like I didn't mix it right or whatever.
So I took pictures of the molds that were so soft they TORE like heavy cardboard just trying to remove them from the models, I also sent them a sample strip and photos of existing molds made of their stuff and these new ones showing the COLOR of the rubber was even vastly different.
The models were bone dry plaster, sealed as always and relased with their spray as always, bone dry terra cotta, also sealed and relased with their spray as always.

I waited about 2-3 weeks for them to finally get back to me and I had to email them during that to find out what was going on. Then when they got back to me they said their lab tests indicated there was an "irregularity" with part B and they were shipping *A* replacement kit, forgetting for the moment that I used 2 or 3 kits for those large molds and that they admitted there was a problem with THEIR product after all, no apology or anything like that.
When the kit arrived I tried that one, and it did the SAME thing!
By then I had already decided to switch, I mean 2-3 WEEKS for them to get back to me and then basically treating me as though it was my fault, that's where I draw the line.


I use fibergalss resin and cloth for my mother molds. $35 a gallon, available at my local Advance Auto Parts Store. Going back to Landseers price costs, it works out a tad more expensive than Plaster of Paris, but is FAR lighter in weight, also stronger, and fiberglass resin does not suck oils

Well a few issues there with that v/s plaster, I actually use hydrocal because it's harder and stronger, it's also cheaper than Plaster of Paris here.

I make ALL of my molds in multiple sections, they are rarely ever less and 4 pieces and most of the more complex ones are in the 8-10 piece range.
I don't care about the weight, the largest section- the base always lays on the table, the rest are all smaller sections and fillers that come off and away from the base, the base holds all the pieces in alignment.
Most of the times I WANT the weight so the thing doesn't rock and slide all over the table while I'm working on the cast.
The fiberglass is probably ok for very flat plaques and two half molds, but two halves rarely could ever work on my models.

[Landseer]

Just to mention you can also think about fiberglass plaster molds. Perhaps you know what I mean. Put a layer of fiberglass mat after the first layer of plaster and next add another layer of plaster.I don't use reinforcement in my molds, they don't need it, but in the past when I did add a wire or other and a thin section got broken, the two pieces would be impossible to glue together because the reinforcement is stretched and the two piece never fit back the way they were.

On rare occasion I had breakage I used elmers white glue and the two pieces fit together well.

[dilida]

Merlion,

Sorry so slow to reply, STUPID computor! But, it's playing nice again and I can answer your question. Kinda. I can't post any pictures yet till I figure out why the pictures I take are so big. Too big to post. The ridges I describe are hard to understand without seeing them, so I'll keep trying. Some artists that visit the foundry and make thier own molds do use this type of rubber, so I know there is some interest out there. If you don't want multiple castings you CAN use a cheaper over-the-counter brand, just don't expect it to last long.

A key knife is also called a channel knife. Instead of a flat blade, it has a channel towards the end. When drawn thru the rubber ridge it cuts a groove, that when the rubbers are put back together, they lock right in place in. Does away with almost any mis-register. I absolutly reccomend it with this method of molds. The one I use is from www.sculpturedepot.com for 20 bucks.

lisa

[GC53]

Just ran across this topic while looking up Black Tuffy info. So thought I'd pitch in my experince with using the RTV's.
There use to be different life years marked on the tubes. My brother who is a taxidermist felt that the 35 yr product (GE SILICON) had the best strength as far as not tearing. Another product that GE made was part number 1201. Came in a white and reddish orange tube for around $4 ea at that time. It was a construction grade silicon. This was used in favor of anything else, but you had to order it out of K.C. Kansas.we live in St. Louis and sometimes would need it right away.
I have put it on straight out of a tube and let it set up. I have also used XYLOL to cut it with to a honey consistency, others have used Charcoal starting fluid. We used warm water and liquid dish soap to put on our fingers by having a bowl mixed up at the table we were working at. This did a good job of keeping the RTV's from sticking to our fingers.
As for a release agent, I just go to the store and buy PAM cooking spray, works very well.Also I always spray some Clear Krylon Acrylic spray over the clay in case it's Sulfur based so the rubber doesn't have a problem not curing..due to the sulfur. When applying Silicon on some larger pieces and even some certain reliefs, I cut strips of Burlap (from Walmart) to add strength to specific areas that might be stressed due to the folds of the rubber mold. I have never used shims on any mold like the kind that are sometimes used, but have used Reynolds aluminum wrap to seperate the mold edges on my plaster mother molds.
Just some thoughts to share. If I can figure out how to do it I'll post a picture of a life size Bullmastiff head study I cast this way.
Gary Cooper

[MedFX]

I used to make waste molds from 100% silicone caulking but found it to be a waste of both time and money. Quantum silicones makes condensation cure 2-part silicones that cost about the same ounce per ounce as even the cheap silicone caulk and work far better. For just a little more, you can upgrade to their addition cure silicones which are excellent in every way. Advantages to proper mold making silicones are: superior strength, flexibility, and stretch; no odor; predictable pot life and cure time; and a long service and library life.

When I did use caulk, I would add 3-4 drops of glycerine and a drop or two of acrylic craft paint per ounce and stir until the color was consistent. I could brush or spatulate this into place and it would cure evenly throughout up to a half inch or more thick. Mixing straight water into silicone caulk is like herding cats, it can be done but what a hassle.

For release I used either Johnson's Paste Wax or petroleum jelly thinned with mineral spirits, but any good non-silicone mold release works just fine.

If you thin it with xylene or mineral spirits you will reduce tear strength and increase shrinkage in proportion to the amount of solvent you add.

Unless you a desperate for a quick waste mold, or your shower stall needs sealing, I'd steer away from silicone caulk.

:)

[insectoman]

so many of these posts read like the people posting them are working for the companies. Landseer cracks me up with how extremely agressive thye are against the subject. I think this sounds like it would actually work pretty well for a low detail sculpt.

[Landseer]

so many of these posts read like the people posting them are working for the companies. Landseer cracks me up with how extremely agressive thye are against the subject.

I'm glad we crack you up, but you will want to keep in mind since you are new here- I have made rubber molds since I was 16 and that's been over 30 years of mold making and I've used it all- latex; a dozen different brands- all crap, all shrink, all take 50 coats to get any thickness, all stink, all are affected by copper, brass, even brass paint. RTV rubbers, tin cured, platinum cured silicone, metal casting red silicone, polyurethane, 2 part, 3 part, 1:1 ratios you name it, red, green, amber- every color and formula in the rainbow from half a dozen or more manufacturers, let's not forget the foam insulation stuff in a can in place of plaster.

When I and other experienced mold makers here tell you;

"Latex is crap stay away from it" or "window caulk belongs on windows its NOT remotely the same silicone" or "Your TIME is worth more and the "savings" for cheap crappy molds that don't work right is offset far more by the time you wasted, the money thrown away having to make another mold, or dicking around repairing and patching every cast"

You can be sure we have USED this kind of crap for molds at some point in our LEARNING curves, and learned from the EXPERIENCE and that is why we rapidly progressed to professional products like Quantum, Polytek or Smooth-on silicone or polyurethane mold compounds.


I'd like to "see" someone do a complex mold of a sculpture like this full bodied 28" long griffin using window caulk or even latex with all those undercuts opposing angles etc- it would be a total disaster. The way you make a mold of this is you use real mold rubber, preferably silicone with it's predictable results. It will probably take 1-1/2 to 2 gallons to properly do it.


http://i23.photobucket.com/albums/b375/Randall2/168-R-12-8-07.jpg

[Jamo]

I would completely backup what Landseer said. Although I would like to add I can see where you think silicone caulking tubes are cheaper because you are paying 5 bucks for a tube that seems to coat alot of sculpture but do the math using the volumes you get and add in the headaches by not using the proper stuff. Go with the professional silicone thats designed for its purpose. There is the larger initial investment if you want the 1 gallon kits and you can also get small sized bottles of sample rubber that will do small jobs. The silicone caulking seems better cause its conveniently obtainable at any dept store and has that small initial cost but its not. The fact is proper rubber molds are expensive and you are going to have to lay down some money to do a proper job, simple as that. If you do it right you can make many, many castings from the one mold possibly thousands. The only inexpensive way to make a mold is to do it completely out of plaster/hydrocal and do simple parting pieces. Landseer has got the experience listen to good advice.

[GlennT]

Landseer and I may not agree about a number of things, but he knows what he is talking about with molds.
Treat your art (and your time) with the proper respect, and do it right. If you have a tooth that needs filing, are you going to save money and get some JB Weld epoxy and fill it yourself? But if your art is worthy, it will live longer than you, so give it your best!

[Landseer]

Thanks Glenn, and Glenn is right there, fact is Glenn and I are like oil and water and at each other's throats- literally- at times on at least a couple of non sculpture issues, but we also agree on many others, so when you see us agreeing with one another on a topic like mold rubber or sculpture, then it should carry twice the weight!

[GC53]

I think if someone is just starting out experimenting with mold making, Silicon tubes from the hardware store would be an in-expensive investment. The sculptures that I have posted pics of (the 2 dogheads and Dracula) are poured out of these rubber molds. The Bullmastiff mold is 17 years old.
Using expensive rubber molds has to be the best way to go, like they are saying.."otherwise ..why is everyone paying the $100 a pop for it".
Barry Johnson, a western sculptor of cowboys indians etc. Was the guy that took the time to teach me how to use them. When I asked a foundry for the cost of making the mold for the Bullmastiff, they said $500.that was 17 yrs ago.
Gary C.

[Harryman]

Just waded through this thread, pretty informative and entertaining.

I've made molds for over 20 years and you get what you pay for.

If you have the time and inclination to screw around with modifying caulk to make molds, have at it. Or if you're a beginning mold maker and want to learn the process and don't care if your molds work or last, fine.

But if you value your time and work enough that you'd rather be sculpting or doing something else besides kneading silicone in a bucket of water while holding your breath, use materials designed for the job.

[Landseer]

When I asked a foundry for the cost of making the mold for the Bullmastiff, they said $500.that was 17 yrs ago.
Gary C.

Most of that $500 quote was LABOR, probably only about $50 was for materials, the rest was time billed for labor at probably $30 an hour.
If you said "Use cheap caulk instead" the savings might have been all of $20.

Shop rate where I work is around $60 an hour, so if someone needed something done and it took me a work day to do it, that's over $500 for labor alone they would be billing plus sales tax and materials. The materials would be minimal in almost everything, it's the labor that costs you through the nose for any kind of custom work.

[Mr. Malloy]

thanks all for the info. I am verry interested to find out how the results are.

[kazjo]

Hi guys,

Can I just ask if we are talking about the silicone tubes that are used as a sink and bath sealant? If so I have used this material (the transparent variety) in making small moulds and am very interested in how you thin it down to make it more workable. Is it white paraffin (the sort you use in oil lamps) that thins it, and also would methylated spirits work as a thinner?
When ever I have used it straight from the tube, I've struggle with clearing the air bubbles as the silicone is too thick for them to escape. Its a shame because I have found it makes a great moulding material when casting cold cast bronze and is pretty flexible for deep undercuts. If I can find a way to prevent the air bubbles I'd use it on all my small sculpture projects, especially as where I live its around 2euro a tube (as opposed to 22 euro for a litre of silicone from the mould making retailers). Hope I haven't repeated any questions already covered, if so, my apologies :o
kjo

[wolff]

If you keep a small container filled with water and a small amount of dish soap, and keep your hands wet with same, you can squeeze the silicone right into the water or your wet, soapy hands. If you then sort of pat it a little bit, then apply it from the center out, you can then pat or push air bubbles out.

I usually apply two coats, each about three millimeters thick. Very lightly patting a single layer of cheesecloth into the top of the top of the first layer will help a lot with tear resistance. Just be sure you get the two layers of silicon to touch, or it`ll tend to separate.

I like to use the stuff too, it`s cheap here, and for small molds or if I only want to pull a few casts, it works great.

Bill
www.billwolff.net

[Landseer]

Hi guys,

Can I just ask if we are talking about the silicone tubes that are used as a sink and bath sealant?


No, this junk has been debated and discussed over and over in many threads, it is temporary CAULK and a SEALANT, it is NOT a mold making material, the silicone caulk is NOT the same as silicone mold rubber, it's like the difference between pressed 1" cardboard with teak grained contact paper applied to the surface v/s solid teak planks- they might both be called wood, lumber, or teak but they are not the same!

[wolff]

No, this junk has been debated and discussed over and over in many threads, it is temporary CAULK and a SEALANT, it is NOT a mold making material...
__________________



There is a time and a place for everything. I would agree with you that if you are making production molds, silicone caulk is probably not the best choice.

But I don`t make production runs of pieces. I don`t cast in concrete. I don`t want molds sitting around for 10 years.

I do like to duplicate modeled forms in wax for casting in bronze, often three or four casts only. And often I manipulate the details in the wax after pulling them from the mold. Silicone caulk works perfectly for this; it is far more cost effective and takes far less time (for me, where I am, doing what I do) than a pourable rubber. And I consistently get accurate fingerprint level detail with it.

There are advantages and disadvantages to both, and times where it makes more sense to make a proper, traditional mold. And there are other times (like taking a mold from a pressed tin ceiling, in situ, for example).

Bill
www.billwolff.net

[luna]

Pound for pound, I think a castable or brushable urethane rubber is about the same cost, offers great detail if applied right, and you do not have to worry about drying time...just 45 min. between coats, and up to 1/4" thickness per coat.

[ashsmoen]

The idea of using water to accelorate the tube caulking from Home Dept is on the correct path. I will expand on that idea. Take a five gallon bucket , fill it with water and squirt the silicone tube in the bucket. Kneed the silicone with hands and it will ball up into one mass. This proccess is washing out the chemical used in the silicone that retards the drying proccess. In about an hour or so the silicone will set up(cure). Before it sets it can be pushed and molded over the form like an RTV rubber. When you have the desired thickness make a mother mold from paster for the mold support. I have seen this used for bust size sculpture with great detail....good luck. Post results for others to see...thanks Louie
Hello Louis Arce, Dilida, And Wolff,
we teach the method you described, kneading the 100% silicone caulk in a bucket of water, to our freshmen 3-D students as a quick and inexpensive intro to mouldmaking. The students this semester are interested in casting something other than wax, namely chocolate. Do you, or does anybody, have any idea as to whether the 100% silicone is food safe for casting chocolate, or will it leach some nasty poison and result in me being responsible for mass food poisoning and jail time?

[Landseer]

_

But I don`t make production runs of pieces. I don`t cast in concrete. I don`t want molds sitting around for 10 years.



Well maybe you have better window caulk than we have HERE in the USA, the stuff HERE is crap, it's not designed to be used this way, it's designed to be used in a 1/4" or less thick bead around window frames and small gaps, it otherwise skins over while fuming out vinegar and the inside stays like chewing gum because the outside has skinned over.
It is also very thick and designed to STICK like glue to objects, silicone MOLD rubber does not.
Window caulk is also on the brittle side- lacking any real stretching ability, it's not designed to be used like a rubber band.

I use silicone mold rubber for waste molds even, where I take ONE cast and toss it out, it's only $25 a QUART and a quart goes a fairly long way unless you are building a mold to be an inch thick with no supporting shell!

[Mr. Malloy]

great thread. I am ALWAYS trying to find a way around the expenses of art making. Has anyone found a wholesale price on the tubes of silicone rubber in tubes? Seems like HD should sell cases for a discount?
Landseer great link to the republican phenomena. thanks

[Landseer]

Hello Louis Arce, Dilida, And Wolff,
we teach the method you described, kneading the 100% silicone caulk in a bucket of water, to our freshmen 3-D students as a quick and inexpensive intro to mouldmaking.


The stuff is not hand lotion, you really do not want this stuff on your SKIN, or the chemicals in it on your skin or fumes in your lungs from it! It never fails to amaze me the stuff people will do with extremely toxic chemicals, xyline, and so forth.
That vinegar stench is acetic acid by the way.

[dilida]

ashomen, I don't know about the leaching aspect of this type silicone, I have read brush-on type, 2-part silicones have a specific food usable silicone. Not sure if it's so you can bake with it or make candy-type molds, but i have never looked into using the 1-part silicone for food.

lisa