making RTV molds: does release agent attack paint or primer?

[356speedster]

I'm making some RTV silcone molds of some parts, but I'm wondering if the RTV release agent will react to paint or primer?

Should I cast before priming or painting, or is it ok to use the release agent without destroying the primer or paint on the master?

Btw: I'm using products from MicroMark.

[rsxse240]

well I too am using the micro mark products. I found that it DOES attack some paints, but I don't know about primer. best bet is to use as little release agant on the painted part as possible, or test it in an inconspicuous place, or other painted part to be sure.

[white97ex]

release agent??? lol. I have yet to use any release agent, working with alumalite RTV

[356speedster]

Originally Posted by white97ex

release agent??? lol. I have yet to use any release agent, working with alumalite RTV

So you just pour the silicone onto the master and it doesnt stick to it?

[hirofkd]

Silicone shouldn't stick to the master, unless the master is made of the same kind of silicone. I always finish the master with Mr. Surfacer or some type of primer, and I've never had any problem. In fact, I don't think you want to use release agent on the master (whether it's spray or brush-on type) because it roughens up the surface, and that will be transfered onto the mold. Release agent is meant to separate silicone when you are making a two-part mold, and also when you actually cast parts with resin.

Even resin doesn't stick to silicone while the mold is new. But the heat caused by the chemical reaction of resin quickly deteriorates silicone. And when the mold's surface gets rough, resins start to damage the mold. That's why you always want to spray release agent every time you cast parts. The expensive Shinetsu brand, which I used to use for commercial kits, lasted for more than 60 shots with a careful use of release agent.

[Lownslow]

im using smoothon an ive molded painted parts before with no damage to the painted master i use a release agent but ony when i cast

[white97ex]

I am going to start clearing my masters with urethane clear I think. This should help fill and imperfections I havn't noticed. I also cast without mold release. I simply cover the inside of the mold with baby powder

[klutz_100]

I agree. You don't need release agent on the master as silicone only bonds to silicone.

If you are making a 2-part mold the you WILL need release agent where the 2 halves of the mold will be meeting (I use regular Vaseline for this)

When you are casting the resin parts you also don't really need release agent but I have found that a light dusting with silicone spray is useful for deep or complicated molds with overhangs etc.

HTH and have fun!