ART 40FS RUBBER MOLD TECHNIQUES NAME ______________
One-piece ‘Brush-On’ mold: Also called a ‘glove’ or ‘cut’ mold.
You will need: Pattern, rubber, 16 oz. cups, disposable brush, spatula, scale, spray release, a stack of paper towels, denatured alcohol (for clean-up) and this hand-out!
- Prepare pattern. Determine parting lines and number of mold sections necessary.
- Apply parting agent: brush on petroleum jelly and/or use a spray release.
- Apply a coat of thin rubber with brush until about 1/16 inch. Wait 15 minutes.
- Apply even coats of thicker rubber (10 oz. ea.) with spatula, up to 3/16-1/4 inch.
- Create a thick bead, or ‘welt’ where the mold is to be cut later.
- Allow to cure overnight (or at least 8-12 hours in warm weather).
- Build a clay wall around the piece for each mold section necessary, with keys.
- Apply parting agent, then mix plaster with jute.* Allow to harden (30-60 minutes).
- Turn over, remove clay, clean pattern, and repeat Step 8 for each section necessary.
- Separate plaster sections and carefully make an irregular ‘zipper’ cut in welt.
*To mix plaster: Use fresh plaster, clean, cool water, and set aside some jute or hemp fiber.
- Use a rubber bowl and use an appropriate amount of clean water, generally about half of the final amount of material desired. (Never fill the bowl more than about 1/3 full of water, in order to allow room for adding and mixing the plaster!)
- Slowly and evenly sift the plaster into the water. Slowly add enough plaster until a “mountain peak” forms and maintains itself for about 30 seconds. (The ratio measured by weight is generally 65 parts of water to 100 parts of plaster.) Allow to soak for 1-2 minutes.
- Mix very well, for about 30 seconds. (Hand-mixing is fine for small batches. For larger batches, use a high-speed propeller mixer, held at 75°, mixing downward.)
- Carefully spread out one thin layer of dry jute in between two layers of plaster.
(Don’t mix jute in bucket with plaster, as it will clump and be difficult to spread.)