I am in the midst of carving my first plaster master (field stone wall) for some scratchbuiling projects in the future. I was wondering about a few things:
A. What do you coat the master with (Durham’s plaster is the base) to keep it in good form prior to lubing it and coating with latex?
B. Since this is my first homemade form, I think I can share it freely… has anyone ever made a form or master swap? I mean, I could make other masters easily once I make the swap and if people liked I would swap with others… would be easy for a bunch of us to do and only would cost shipping… just a thought…
Joel Bragdon has a formula for making latex molds. He brushes 4 to 6 coats allowing the latex to dry between coats. He sells the latex as well as the molds. Try his website at www.bragdonent.com. We purchased one large mold and two small ones which should allow enough variation for our entire layout.
I made some rock molds from real rocks. I used silicon spray on some and others I sprayed with gloss clearcoat. Both worked fine for rocks. I tried to make a mold from a commercial hydrocal casting and it turned out terrible. I sealed it with silicone but the latex still seemed to suck into the hydrocal. It was very hard to get the mold off the master. Distorted it really bad and made it useless. I would recommend using clearcoat on the master and using a better grade of latex than the Woodland Scenics stuff. I’ve had coats of that stuff seperate from each other after it dried.(I’m no expert at this so take it with a grain of salt)
I would use the acrylic gloss for a sealer. Instead of painting on layers of the latex, have you considered using RTV.
The RTV mold can be used over and over w/o ever worrying about tearing or misshaping as does latex. RTV works best to lay master on smooth surface wax paper or cooking spray for release, dam around the master with the dams just about 3/16-1/4 thicker than master, then pour. Pour slowly from center and let spread to fill and level. The advantage of this is, the finished mold will have a perfectly flat back to produce flat replicas. No proping up the mold to eliminate distortions in the copy. It is very flexable and evn odd very irregular castings can be worked out of the mold with no damage to either.
Looking back through the posts on mold making,the consensus is you don’t need to coat the MASTER with anything if its plaster based. Dave Frary sprays the MOLD with wet water before casting to facilitate the flow of plaster. I think the big thing with a lot of the rubber compounds both latex and RTV is to avoid contact with sulfur containing substances.
Spraying the mold before casting is different than coating a master w/ a sealer or release to “make a mold”. The only reason to seal the master is not to have any latex bond into porous or detailed areas. This isn’t that much of a problem with the RTV.