Fiberglass Instead Of Plast Paste?


Well-Known Member
Well I just noticed Is kinda expensive even though you buy the trial size kit

But I was wondering,

can I make the outer shell with fiberglass instead plasti paste???

Will the rubber resist the fiberglass resin???

and if it worked, what extra things will I need to make it work (extra release agent etc...)????


Well-Known Member
Alot of people do that, don't ask me how to do it, cause I haven't even molded yet. lol. I think theres a video on youtube with Ithica and Sigma where thay use a Fiberglass shell.


Well-Known Member
Well I will try to look for it tomorrow, I was just wondering because tomorrow I will get some clay and brush on rubber.

I was going to order plasti paste but its to expensive and I have alot of fiberglass mat lying around :p


Jr Member
Are you saying you want to use the fiberglass as the outer shell of the rubber mold so that it doesn't lose it's shape?

if so (even if people might have already done as afore mentioned) i have never thought of it, and it seems like a brilliant idea!

The only issue i can think of off the top of my head is that the fiberglass resin might eat away at the rubber mold! Cause i believe i have heard that it eats away at stuff like cups etc... =/ not entirely sure though, so there is still hope!

Let me know how it turns out!

Brandon McClain

Well-Known Member
I use fiberglass for all of my mother molds. There is no problem with it reacting to the silicon. If you want a good video, check out Ithicas vid on making his recon helmet mold. Its a good one! You can also check my reach wip thread for some pics.

UNSC Leatherneck

Well-Known Member
Yep, fiberglass makes a great mother mold for silicone molds. No worries about the resin eating the silicone, either. Most people I know use the fiberglass because it is MUCH lighter than plasti-paste. Newspartancreator likes to use a three layer fiberglass mother mold. Remember to apply a mold release (Vaseline works). The first, inner layer is woven fiberglass cloth. You cut it into sections (3x5 inches or so) and wet them out onto the silicone mold. Then you come back with sections of fiberglass mat, which is a bit stronger, but doesn't drape as well. The final, outer layer is woven fiberglass cloth again. This process produces a light, strong, smooth mother mold that will last the life of the silicone mold. Also, don't forget to make the separation line. For helmets a "mohawk" usually works well. For casting, you need a way to hold the two halves of the mother mold together. Drill holes in the "mohawk" and use zip ties to secure it.


New Member
I was just at my local TAP Plastics this weekend and they recommended fiberglass as a mother mold for the silicone molds I will be making. Granted, they wouldn't be likely to recomment a competitor's (Smooth-On) product, but the people there know a lot about what they are doing.

@UNSC_Leatherneck: I was told that I would not need a mold release between the fiberglass and the silicone. It was one of the reasons I went with it over Urethane rubber which was slightly cheaper. Is this a "just in case" step?


Well-Known Member
Thanks leatherneck :D

I tried the fiberglass, and didnt use release agent, but the ruber comes off.

I made a small piece so I didnt really cared what happenes to the fiberglass or rubber


New Member
HI guys, Im looking for an alternative to using fiberglass on the outer shell of the mould. Some people have mentioned plaster, is this normal plaster of paris? and how good is it?