Casting Hydrocal white

[Pale Comparison]

Good morning,

I finally made my first brush on mold, a sculpture about
5 inches high, and is not working so great i have casted ten pieces of which only two look ok

My problem is that when I cast with HYDROCAL the nose always has an air bubble, which leaves the sculpture with a portion of the nose and lips missing once out of the mold. The waist is pretty thin and it usually cracks in half also. any suggestions please

Is there another easily mixed medium like resin or gypsum I could use to cast with minimal bubbling or cracking ?

Is there anything I can use to build the nose up other than the hydrocal( dries very fast itself ?

Please and Thank you :confused:

[fritchie]

I have not used Hydrocal, but I have used plaster, which is similar. I recommend using a brush or spatula to push your material into tight corners or critical areas such as nose, lips and eyes before adding the bulk of the casting material. This ought to circumvent most problems of this sort.

Hope you also get suggestions from someone who has more experience with these materials!

[Pale Comparison]

Thanks Fritch it still didnt work for the nose ... ...but I have figured out somethings on my own the plaster Hydrocal white should be mixed at 70 :100 water / plaster ratio and plaster should sit in the water for about to 3-4 minutes prior to mixing although I have cast about 12 there are only probably three that i can salvage if i am lucky with a littel re- working with the hydrocal ( one thiing i will be looking into is dentist materials fillings and stuff)

Tonite i will try coating my sculpture with a thin layer of vaseline ..

I will continue to look for a quality casting material

Thanks again, i wll post a picture when i am done

[fritchie]

Good Luck! I look forward to seeing your picture.

[sculptor]

here is a link (http://www.plastermaster.com/usg/plasterfundamentals.htm) to the usg site for hydrocal----

I mix as directed, sprinkling the hydrocal slowly into the water(I use warm water for a faster set)---then mix for 5-8 minutesslowly and gently so as not to introduce any more air into mix, then pour into mold and wash arround and pour excess out, then repour and etc, once all the undercuts have been sufficiently filled, I fill the mold and set on a vibrating table which encourages any trapped air to float to surface------test your set time----and stop playing ehen the mix is near the set time, or it makes it weaker-------also
you can get hydrocal with glass fibers for added strength----then i take a hike and let it set for several hours before demolding---I shoot for a set time in mold for 6-8 hrs----as the mix cools it hardens----let it have it's time

cool?
Rod
Sculptor (http://sculpture.alturl.com)

[fritchie]

If you pour this in and swirl it around to coat the entire surface, then pour it out and so on, I don't see how you can get bubbles on the nose or elsewhere. Maybe you’re adding too much the first time, so that the bubbles are invisible to you. Your working method seems fine to me, but maybe you should add a smaller amount in the first pour.

Let us know how this develops. I’m sure your experience will be helpful to others.

[Pale Comparison]

Good evening,

I have included photos below,

Ok, it definitely looks like I am going to have to touch up a lot of them any ideas of what I can use beside the hydrocal itself,

I will also have to glu the casts which broke in half with some kind of cement glue ??

here is a summary of my experience with hydrocal so far

Mixing technique 70:100 then let soak for 3minutes ///mix for two and then pour


The technique which is sort of working for me is :

1 ) use a paint brush to coat vaseline on the inside delicate tiny parts such as th nose

2) second while the mold which is two parts is open pour hydrocal in the head and tap it on table until air bubles pop up and push hydrocal in with paint brush (thx Fritchie)

3 ) then i close the mold and pour the rest in a portion at a time

4) I have been timing but it seems like once the mold is closed after head is poured in the stuff begins to set and never reaches the arms so she ends up with partial arms

5) bottom line I will continue to cast because i am not sure what it is but i can t stop until i get another perfect cast ( you know i did mange to get one)

ok that was mine now correct me if i am wrong but you are suggesting that i first whil mold is open( please refer to photos below)
pour hydrocal one thin coating all over , second and pour excess off then close mold and pour the rest.

I will try this tonite and let you know how tha transpires


lastly do you have any suggestions on hwat I can use to paint this stuff acrylic does not seem to work well



http://members.tripod.com/paulk28/open_mold.JPG

http://members.tripod.com/paulk28/closed_mold.JPG

http://members.tripod.com/paulk28/side_by_side.JPG

[fritchie]

These pictures help a lot, and I really think you might want to make a new mold either from the original, if that is usable, or from a good, probably refinished, copy.

If this mold really is two parts and not three, I think you always will have trouble with it. If fact, I don’t see how you can even go over face parts with Vaseline. This figure is very complicated for casting and molding, but obviously people with experience are able to cast pieces this complicated and more so.

Most often, a two-part mold has a front and a back, each covering approximately half of the piece. This looks like there is only one piece above the very narrow waist, so the waist becomes a trap for both brushing and pouring.

My suggestion for this mold is to pour a small amount of material into the mold almost as soon as it is mixed, while it still is fairly thin. Swirl that around fully, so it can coat the complete inside, but with special attention to getting material into the face. (Patches will be less noticeable in the hair.)

After this first application, add the rest of your material as soon as you think it will set adequately.

One problem you may be having, with such a small mold overall, and with the thin waist, is that Vaseline may be lumping in tiny areas such as the nose. It would be a bit risky, but you might try thinning the Vaseline with some solvent to reduce likelihood of lumping. I’m not sure what to use, probably a light mineral oil such as is used for electrical motors, or mineral spirits. Vaseline basically is a very heavy oil, so those materials should mix OK.

I don’t have suggestions on painting, but someone here must use Hydrocal and may be able to help. Your problem may be residual Vaseline. Nothing will stick to that. Possibly a good (and careful!) brushing or washing with mineral spirits before painting.

[oddist]

Bubble problem?

This may or may not be of any help in plaster casting and I'm open to any other inputs on this...

There is a technique used by urethane casters where they put poured molds into a "vacuum chamber" to either remove the air in the liquid by drawing it to a waste surface, like the bottom of a sculpture, or shrinking entraped air bubbles to some less visible size.

[sculptor]

Nice work

As you pour pieces with thin areas(your waste) ---(If you have my luck) you should count on discarding up to 25% for an example...see my Nelly-----
If I cast 6 pieces in a run, I'll have flaws in at least one(usually voids at chin or under breasts-----she has a 2 piece mold poured from the bottom of the base), and sometimes 2 and breaks at the knees are common...---for her, I pour in hydrocal of casting plaster, and dump a little glop on the desk-----then I rotate the mold as I pour a little of the material back out into the bowl----when the inside of the mold is completely covered, I lay her on her face (on the vibrating table) with base elevated 20º, to thicken the material in face and breasts---then start mixing the second batch. I keep testing the glop on the table as I mix, and when it is beginning to set up, I set her in a bucket (bottoms up) and fill her as she viabrates, tilting her around in a spiral within the bucket to help remove any trapped air----when I feel good about this, I wedge her in and pour to the top of the base, turn off the vibrator, take a moment to clean my mixing bowls and tools-----and go do something else--------when the blob on the desk reaches the point where it rings when I hold it up and tap it-----and/or resistd denting by a thumb-nail, the mix in the mold is almost ready to demold------touchups-----carving, scraping, patching, etc., are easiest while the plaster/hydrocal is fresh---so when I'm doing a series, retouching the last one is part of what I do when I'm going and "doing something else"---------

fritchie-----It looks like a complete 2 piece mold----the right-hand piece is curved backward following the contours of the sculpture

practice
hope this helps----
rod
sculptor (http://sculpture.alturl.com)

[fritchie]

Thanks for the observation on the mold, Rod. I had overlooked the "wings" or arms on the left-side (front) part of the mold. I also realized after yesterday’s post that casts couldn’t have been removed if I were right about my earlier supposition.

[Pale Comparison]

Excellent advice ! it worked ( see photos below) the first time only slight imperfection on the arms but i expect that because this is my 1st mold (and that's another story! )

but coating the inside with hydrocal while it's wet worked very well in not leaving any bubbles at the top of the nose OR Chips and the face is nice and smooth


I do not have a vibrtating table but i hit that mold on my table more than a few times ....let it set fort 3hrs and voila not too bad

I will re-work the arms with some hydrocal but unfortunately, i am a working stiff so i will have to wait til the weekend to re-work

I will now research painting this stuff ,,, I will post my results once painted

BIG THANKS :)



http://members.tripod.com/paulk28/side.JPG

http://members.tripod.com/paulk28/front.JPG

[oddist]

Glad it all worked out. Nice. Be sure to post the finished piece.

I learned something out of this too.

I never heard of using a vibrating table to deal with air bubbles in plaster casting. Makes sense. I would compare this technique to the use of vacuum in urethane casting I brought up in a previous post.

I hope others learned something here too.

[fritchie]

Congratulations, PC. I've been away a day or two, but I'm glad to see you got this result. The new cast lets us see your ideas better, too, and I like the piece. Very fresh and active.

[sculptor]

I went to the plaster supplier friday while de-installing(or is that disinstalling?) the davenport mermaid and asked for hydrocal
they din't carry it anymore, but he sold me some ultracal 30 uses even less water 38lb h2o for 100 lb plaster----has higher strength and lower shrinkage than hydrocal-----is a mix pf 96% plaster of paris, 3% portland cement and 1% silica

(wild guess) low shrinkage is due to low h2o content in mixing consistency

new product for me-----I'll try casting a few in a couple weeks and report results-----sometimes i'll mix the hydrocal and molding plaster----will try that with ultracal also

.........just when you think you got it all figured out------

merry christmass happy holidays and welcome new year.
now, the days start getting longer and with any luck at all, the cold ends before the woodpile ends

rod
sculptor (http://sculpture.alturl.com)

[Pale Comparison]

Thanks again ...your help definitely got me this far

Ultracal sounds interesting I am not that impressed with hydrocal for cement it is pretty week product..... I am very interested in finding out how that ultracal works out

I have now moved on to fixing the 12 broken casts ...

so far I have not been having any luck with any glue including probond, weldbond and 5 minute epoxy nothing works 25 dollars waisted

Can Hydrocal be glued together the pieces are broken at the waist....I thought glue would work anyone ever glue this stuff before ?

Please advise

[sculptor]

when I've repaired plaster/hydrocal casts, I've drilled holes and inserted thin dowels and or wires, then moistened both surfaces and used more plaster/hydrocal as the glue---if you can scratch deeper holes to create more dimensions of purchase for the patch material, it works a tad better-----one such repair rebroke in the same place 3 years later when dropped-----but was un-noticable till I saw the old dowel repair------