I'm a little confused ... are you pouring resin over the polystyrene blocks or are you just molding the blocks so then you can reproduce the carved blocks much faster and efficient with resin? Or after the resin is cured, will it affect the polystyrene somehow chemically?
So we've used polystyrene plastic strips as mold boxes for both resin and rubber before without issue. The urethanes will try to bond to it unless you apply mold release ... UMR or Stoner. Also make sure the polystyrene is not porous ... IF it is ... the resin and rubber will flow into the block and lock on to it. If it is not porous, the silicone rubbers will not bond to it (no mold release required).
If you are talking about cured resin next to the blocks ... they should not have any effect on them as they are both cured inert materials.
Sorry for not being clear. I guess I need to think more before I type :-)
One goal is to carve a piece and then skin it with resin so I was mostly concerned with how the mixed resin and hardener, in it's liquid state, would react with the polystyrene.
For a one off part, this would save resin and weight.
Also a solid bond with the polystyrene would be a good thing.
Another question that occurs to me is how thin could I make the skin?
To make sure I understand, to use the carving as a positive model for casting duplicates I would want to somehow finish the block with a smooth, hard, non-porous surface and then making the silicone mold would not require a release agent.
For coating applications you have lots of options ... Amazing Clear Cast is what we use for bar top coatings and other cosmetic, high gloss surfaces. The Amazing Clear Cast has a long open time and over night cure. You can also use the quick cast urethanes such as the AlumiRes (RC-3) or White. They cure very quickly but pour like water (very thin).
Porosity of the polystyrene foam may cause issues with bubbles as the resins try to fill the porosity when you are coating and the air tries to get out of the porosity.
As we say ... before doing a big project ... test the material compatibility as well as the process you intend to use on a smaller non critical piece to verify the result you are looking to achieve.
I think this thread might answer my question but need to be sure. I usually use silicone molds for resin, but have a project with many pieces (coasters) and would like to pour many pieces at once. I don't have that many silicone molds.
I can purchase polystyrene petri dishes to use as molds in quantity very cheaply and would appreciate advice. I need the product to be clear, pretty durable and scratch-resistant. What resin can I use, hopefully one that wouldn't require mold release if possible, although the other factors are more important and I'll use release if I have to rather than use a resin that doesn't fit those criteria.
Post by carol - Alumilite Corp on Nov 9, 2017 8:08:39 GMT -5
The clear as with all our resins are polyurethanes, we have one that is an epoxy that is the Amazing Clear Cast. They both will bond to anything but silicone without a release agent. Stoner release that we have in our product line is typically used when pouring the resin into anything but a silicone mold Brian. The resins are not scratch resistant, they are durable, and will be clear with degassing by vacuum or pressure. If you decide to go with a silicone mold, remember silicone gives you what you give it. If the original is not of a high gloss you will produce a matte finish mold and in turn will have a "frosted beer mug" clear as opposed to water clear. Mike's statement of test is always best is the one to follow!
Brian there is some great tips, tricks, and techniques on using the clears right next to the product, by the SDS sheet under technical information.