Using Fiberglass...

Okies.

What type of material have you guys used to make a negative mould for making fiberglass props? Something that can be used over and over. Silicone? Urathane? Latex? I cant seem to find the info I need.

I have been studying online a great deal and I cant seem to find as mnay refferences on fiberglass as other methods.

Any links to information you may have would be greatly appreciated. Thanks in advnace.

 

Buy The Prop Builder's Molding and Casting Handbook by Thurston James. The book is essential if you take the hobby seriously.

Short answer: All the materials you mentioned will work fine as a mold. Hard castings like fiberglass work best with a flexible mold and vice versa. Hard molds can be used if there are NO undercuts, but it is much more anxiety inducing when you try to separate them. It's recommended to remove fiberglass from a hard mold after a few hours, when the casting is "green" (meaning still somewhat flexible) and then rested back into the mold so it doesn't warp, OR wait several days for the minor shrinking caused by the cured resin in the hopes that it will be easier to remove.

Your choice of mold material depends on your own preference. Silicone and RTV rubber will hold up after several castings. But no mold will keep its detail forever if it's being used over and over.

 

Great info. I can see that hanging on to the original model is crucial now if the molds arent indefinate. Thanks.