Hey all-
I have been having some problems with my resin casts and was hoping that one of you could help. When I mix resin and pour it into the mold, the resin in the mold does not harden to an off-white hard color. Instead, the resin "dries" after 45 min. to a medium tan color that is semi-solid, much like tar on a hot day in consistency. However, the resin in the pour cup dries to the correct color and consistency within 5 minutes, as per instructions. I am using Alumilite two part resin, Alumilite mold maker, plastic measuring cups and popsicle sticks (included in kit), and paper Dixie cups for mixing. Also, on my first attempt, I added baby powder as a mold release thinking it was talcum powder but afterwards I read that it is corn starch. My question is what am I doing wrong? Could it be the baby powder fouling things up? Am I not doing something that I should be?
Thanks for reading.
Kyle

Have you washed your molds recently? Mine always sweat a little residue over time. I don't use any powder either.

Paul

Sounds like your resin is too old. It should have a shelf-life on the bottle or in the instructions that came with it. When it gets old, it looses its ability to react and harden. It also gets a dark tan color and can stay soft, or have a soft center. I would replace the resin. Sounds like everything else you are doing is correct. Could be the corn starch in some weird way. I don't use anything for a mold release. They pop out of the RTV molds without problem.

It sounds to me like something in the mold is inhibiting the resin’s cure. It could well be the baby powder. There are certain resin/RTV combinations that don’t work well together but because you’re using Alumilite’s kit (I’ve used this same stuff myself without any problems) I don’t think that would be the problem.
I’d follow Paul’s suggestion and clean the mold thoroughly and then try to make a cast without any release agent of any kind (normally it isn’t necessary with softer RTV rubber molds anyway). If the part won’t demold easily then try using dish washing liquid thinned about 3:1 with water. Paint this on the mold halves and let it dry completely (you may even want to bake it a low temp in an oven for a while) before you pour the resin. I’ve used this technique for years with very good results.
My guess it that this will fix your problem. If it were just the resin that was bad I would expect the quantity left in the mixing cup would fail to cure properly as well but you never know.

Mark

Thanks for your replies gents.
Paul, I just washed the mold and will be making another attempt soon.
Gino, I checked every bottle in the kit but to no avail at finding an use before date. I did check Alumilite's website and they said it has a shelf life of 1 year.
Mark, thanks for the advice on how to get the part to demold if it sticks. I would have never thought of that.
Thanks again guys. I will ask if I have any other problems.
Kyle

I use other brands, but I guess the principle's the same. This sound as either :
- resin is over its expiry date
- resin was not properly stored (open jar ?)
- something influenced the curing process.
- you didn't mix both components in the correct amounts.

One thing puzzles me, though : the residues in your pour cup seems to be ok.
I suggest you try to mix a small amount of the stuff in a different container (e.g. in your pouring cup) and make sure you use the correct amounts. See if it cures correctly. If it does, the problem is not with the quality of your resin., so you can work it out by trial and error. Probably something that pollutes the curing process then. Find the culprit.
If the mixture doesn't cure correctly under "lab-conditions, it won't work in your mold either. In that case, you'll need new resin.
Good luck.

that's strange indeed...
the first thing that comes to my mind is that the resin did not get mixed properly; but if that's the case, it's usually the stuff left on the mixing cup that doesnt cure properly...