How to make Latex Rock Molds Wayne Perrier O Scale West 2008 - PDF document

How to make Latex Rock Molds Wayne Perrier O Scale West 2008 California Central Coast Modular On30 1 Why ? Q: With such commercial variety available, why make your own? A1: You have a lot of time to kill A2: You like making things from scratch A3: You want your scenery to be unique A4: You appreciate the variety of Mother Nature A5: You need / want something you just can’t buy A6: All of the above O Scale West 2008 California Central Coast Modular On30 2 1

Prepare your Toolkit • Spray bottle filled with water • “Dust-off” canister (for cleaning prototype master) • 1 inch (disposable) brush • plastic container (for cleaning brushes) • cheesecloth roll (buy at any hardware store) • scissors (for cutting cheesecloth) • paper towels • liquid latex (woodland scenics works well) • digital camera (always take pictures of the rock area) O Scale West 2008 California Central Coast Modular On30 3 Typical Prototype Rock Outcropping • Lots of fissures and individual rocks visible • Significant depth to formation O Scale West 2008 California Central Coast Modular On30 4 2

Unsuitable Rock • Stone is relatively smooth, few fissures, not much detail • Stone doesn’t “scale” well O Scale West 2008 California Central Coast Modular On30 5 Suitable Rock • Stone has good fissure detail; is quite rough and textured • Scales well O Scale West 2008 California Central Coast Modular On30 6 3

Suitable Rock • Stone has good fissure detail; is quite rough and textured • Scales well. • I made 6 molds off of this one rock O Scale West 2008 California Central Coast Modular On30 7 Example: Original Rock Face • Choose a clear, sunny, dry day. • Use Dust-Off to clean the rock free of debris and dirt • Lightly spray rock with water to provide a good base for the latex rubber O Scale West 2008 California Central Coast Modular On30 8 4

First Detail Coat – wet • Use paintbrush to work latex into all details including fissures • Apply latex immediately after water spray • Don’t worry about thickness of coat – goal is to pickup all details O Scale West 2008 California Central Coast Modular On30 9 First Coat – “dry” • Let first coat dry at least 24 hours • Want no pockets of uncured latex O Scale West 2008 California Central Coast Modular On30 10 5

Second Coat – wet • On second day, spray with Dust-Off to clear off debris and dust – this could gum up your paintbrush and liquid latex still in the jar • Apply second coat, heavier this time than first coat • Goal is to give mold some body. The color should be more opaque this time with little rock showing through. O Scale West 2008 California Central Coast Modular On30 11 Second Coat – dry • Again, let 2 nd coat dry a full day. If there are any uncured pockets (in thicker areas, normally where fissures are), let dry further • Note the color of the mold now. • If some rock still shows through (thin areas), a 3 rd or 4 th coat may be required. O Scale West 2008 California Central Coast Modular On30 12 6

Third Coat with Cheesecloth – wet • The cheesecloth coat provides strength to the mold • Cut squares of cheesecloth large enough to cover ½ of mold surface area or more • Apply thick coat of latex to entire mold area in same manner as previous coats • Lay cheesecloth over this wet coat and “work it in” using the paintbrush. It may be necessary to apply more latex to the outside of the cheesecloth. O Scale West 2008 California Central Coast Modular On30 13 Third Coat with Cheesecloth – dry • Let the last coat dry 48 hours if possible • Extreme care must be taken in removing the mold. • Start at one end and gently lift the edges around that end. • Work your way across the mold, never letting the mold stretch (and possibly rip). O Scale West 2008 California Central Coast Modular On30 14 7

Resulting Mold – underside detail • This was a fairly large mold. These can be difficult to work with • After mold release, carefully pick out all rock debris from the latex, taking care to not stretch any area and possibly rip detail away. • Hit mold with Dust-Off for final cleanup • Congratulations, mold is now ready to use O Scale West 2008 California Central Coast Modular On30 15 Other Possibilities “Glove Mold” • Allows 360 degree casting of an entire object • Useful in “standalone” cases, like a boulder in a stream • Useful for low-weight situations, like modular railroading O Scale West 2008 California Central Coast Modular On30 16 8

Original Stone and Latex “Glove” • Note: Latex glove has no cheesecloth. This is because it needs to stretch for removal. O Scale West 2008 California Central Coast Modular On30 17 Glove Being Filled with Hydrocal • Pour “soupy” Hydrocal into glove and use a paintbrush to work it into all the detail areas. Fill about 15% of glove. Quickly place paintbrush into water and rinse. • Swirl Hydrocal around glove, trying to coat all sides evenly, until it stiffens. Repeat with a second or third coat, after first waiting 24 hours, to buildup a 1/8” thick shell. • Let dry at least 24 hours O Scale West 2008 California Central Coast Modular On30 18 9

Original and Cast Stone • After Hydrocal is dry for at least 24 hours, fill with “Great Stuff” expanding foam insulation • Wait at least 24 hours before peeling off the glove. Do not trim Great Stuff foam for at least 72 hours. This allows the foam time to fully cure. • If you peel the glove before 72 hours, the boulder could implode O Scale West 2008 California Central Coast Modular On30 19 10