Tackiness troubles!

[Stevem]

I am having the worst trouble trying to get rid of the tackiness on a piece after I cast it. I am trying to cast a clear polyesther. I have changed my vacuum chamber to a pressure pot and I am not having problems with clarity anymore. However, I can not seem to get rid of the sticky coating that is left. I have tried to vary my catalyst percentage, but to no avail. I have been told it is the styrene reacting because I am casting in a closed container. How can I overcome this and still maintain the clarity? I don't see anyway of venting off the styrene gas in a closed container. This sculpture needs to be clear and I need to cast 40 of them. So alot of clean up is not lucrative. Is there another product I should look into?

I hope someone can help me before I lose this account,
Steve

[Merlion]

Steve, Have you tried wiping the tacky surface with acetone ?

[Stevem]

Hey Merlion. yes I've tried acetone, MEK, and mineral spirits. I have even flashed them with a propane torch, Ive tried a heat gun and even put them in my oven, all to no avail! I'm in touch with a smooth-on supplier now that says I should use Urethane, with a tin sil mold. Not sure which way to turn.

Thanks for your reply though,
Steve

[Landseer]

Polytek makes "Polyoptic" a water clear resin, not sure if that's a solution for you or not.

[Merlion]

It is interesting that this residual surface tackiness occurs only when no powder is mixed into polyester resin.

On the other hand, there are different types of polyester. My supplier recommends one type for casting, and another type for making fiberglass pieces. It is the latter type that I notice leaves sticky sufaces.

I'm just throwing ideas out Steve. Epoxy resin and acrylic are two other common types of clear resin used for castings for say decorative items.

[Daniel]

Check that you are using the right resin. The clear casting polyester resin that we use at our shop is specially formulated for casting. When they cast clear polyesters here, the parts are always sanded. The pieces always end up either being a little sticky or having "alligator skin" texture in spots due to the material shrinking away from the mold surface as it cures. Polyester tends to shrink quite a bit. If you want parts that look great right out of the mold, you should use a clear urethane. One time I had some leftover silicone that I didn't want to throw away, so I poured it over this scorpion from an insect collection. I poured a clear urethane into the mold and set it in a pressure pot to cure. The piece that came out was amazing. This perfectly formed, crystal-clear scorpion that even had hairs!
Your molds should be platinum-cure silicone, as there is methanol in tin-cure silicone that can inhibit the cure of clear urethane. You will end up with a sticky surface.

I have had good luck with BJB products. There are different formulations for different part thicknesses. If your sculptures are small, use a faster-setting resin. If they are thicker, use a slower-setting one.

[PAULHT]

I suggest using steel wool! Lots of elbow crease but........

[Billy James]

If you are using a laminating resin for casting, I don't think anything will provide good results. I use Silmar casting resins. I don't like the optical characteristics of clear urethane for artwork. If all you need is clarity, but not artistic quality, it would be fine. Do not use a poly resin with curing wax added.

The pieces I make are almost always sanded, but there is a trick for getting a decent surface cure without sanding. I have used this with success:
To avoid the nasty surface wrinkling, be sure that your mold is warmer than your resin. This will cause it to cure at the mold surface first, then shrink away without the nasty wrinkling.
To cure the surface, put the pieces under an infrared heat lamp overnight. Turn the pieces (or move the light) every few hours until the surface is no longer sticky. It usually takes a day or 2. I use a 300 watt heat lamp at a distance of about 2-3 feet from the pieces.

Good luck.

P.S. AFAIK it is the moisture and possibly some of the gases in the air that inhibit the cure. Resin cured under vacuum has little to no sticky surface. Someday I will try a dry Nitrogen blanket, but my work demands sanding in almost all cases.

P.S.S. Smooth-on is a (very good) urethane supplier. Of course they will recommend a clear urethane. ;)

[Gravlore]

Spray or wipe with PVA (poly vinyl acetate) let dry then warm water to remove. it will look like a blue or green saran wrap when dry. I know my post is late but someone else might find it useful.

[Lab]

I am having the worst trouble trying to get rid of the tackiness on a piece after I cast it. I am trying to cast a clear polyesther.



Hi,

I am not sure exactly what type of clear polyeseter resin you are using, but the kind I use always have the same problem you are talking about. However that is what the resin I use usually does. So I tend to produce work that is very low in surface detail (because you will lose about 1/4 thickness when you sand it down) I don't know if you are producing work with the intent of showing high detail, but the resin you are using may not be the one for your project.
try this site for product references http://www.eagerplastics.com/

[EJB]

Industrial Polymers in Houston Texas. ICE.

[evaldart]

When I have had issues with tackiness that won't go away I have exposed the whole thing to significant heat via lamps or hot blowers. The typical french-fry infa-reds work great. position them about the piece close range (not too close) and move them about throughout the day. This usually forces the cure through from my experience.