Brush-on Silicone Rubber - Anyone use it to prep a body for casting?

Saw it at Michael's crafts last week when I went with the TM. The silicone rubber I have right now sets up pretty fast and sometimes retains little bubbles here and there - particularly under wheel arches and window sills.

It would *seem* that using the brush on silicone would eliminate the bubbles at the surface of the master - then you could pour the rest of your mold without fear of bubbles and not having to build / buy a vacuum / pressure chamber.

Anyone got experience with this stuff?

:confused:

Brush-on Silicone Rubber - Anyone use it to prep a body for casting?

Saw it at Michael's crafts last week when I went with the TM. The silicone rubber I have right now sets up pretty fast and sometimes retains little bubbles here and there - particularly under wheel arches and window sills.

It would *seem* that using the brush on silicone would eliminate the bubbles at the surface of the master - then you could pour the rest of your mold without fear of bubbles and not having to build / buy a vacuum / pressure chamber.

Anyone got experience with this stuff?

:confused:

Tried it once , one tip do not POUR any amounts at all will take weeks to cure its strictly a brush on type deal. I thought the same thing was all WOw quick I likey, then when the master was covered and had a good coat I finished filling the box with it.. well 3 weeks later I demolded it and it was still tacky...but its like a 1/3rd of the price and I will revisit it someday, maybe for a small parts mold for testing purposes. let me know what you try and perhaps with others we can find a good use for this product.


Dave

What you can do is mix up a small amount of the silicone you are going to make your mold out of and brush that on let it dry then mix another batch and pour the mold. Also try pouring the silicone from 18inches above or higher so that it pours a small thin ribbon of silicone this helps eliminate bubbles. The best thing to do is to degas the silicone before pouring and degas after. You will need a vacuum pump and a vaccumm sealed container for the silicone and a vacuum sealed container that will hold the mold after pouring.I bought nie at walmart and us an automobile ac vacuum pump.

Roger Corrie

OK - Thanks for the replies & tips.

Making a small batch of the rubber I have now would not work due to how quickly it starts to set up. I do pour from a good height above my mold box but I still trap bubbles. I just need a slower setting rubber, I think. I'm using some type of Ooo-Moo and it starts to set about two minutes after you get a good mix completed.

I've found that re-pouring the 'top' half of the mold (female side) can sometimes reduce the bubbles, even with this quick-set stuff. Or even re-pouring only half that side (say up to the top of the fenders), letting it set up, and then finishing the top off with a second batch later.

What Roger said. Also don't know if two different types of silicone rubber would "like" each other or not. Simple fix on a continuing bubble problem. If your mold is not the problem, but you continue to get bubbles in the resin. This will work most of the time. Cut a vent hole in the problem area. make it a "v" if it is possible. Small end of the V would be at the end of both sides of the wheel well for example if you keep getting a mess, voids or thin resin in that area. When pouring, the problem resin bubbles can vent upwards. Easy to cut the small end of the "V"ent off and sand it smooth.
If you have holes in the rubber that are making voids or bubbles in your casts, clean it up with soap and water, blow dry the rubber. Mix up a small batch of silicone, overfill the hole just a little bit, reinsert the master in the mold and let it dry. Should take out most if not all of the problem. Here is another quicky bubble fix, not as good as the others, but it is quick and dirty. Cut the bubble off your cast piece. Get as much of the bubble as possible. Stuff it in the hole in your rubber. Now on every cast, coat the rubber with baby oil making sure you coat the resin you stuffed in there. You will still have a bit of a blemish in that area, but there is no waiting.