Geodesic Foam Commonly Asked Questions
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1. Why does the foam resin react so quickly and can it be slowed down? Foam resins do react quickly because of a catalyst in the “B” resin. If the amount of catalyst is reduced to slow the reaction the expanded foam will shrink. A better way to slow down the reaction is to chill the resin bottles to between 50 to 60 degrees F. an hour or so before use. Keep them cool in an ice chest while you are working.

2. Can the rock castings be kept pliable after they start to harden? Yes, keep a hair dryer or electric hot air gun handy. Warm air will keep the castings soft and pliable as long as necessary to form and attach them to the scenery base or hard shell. Keep the heat low; too hot will scorch the castings.

3. Can other mold releases be used on the rock molds rather than petroleum jelly and spray paint? Yes, there are silicon and oil based spray mold releases on the market which will work. They are easier to apply but are more costly. Some resist paint and have to be washed off before gesso and paint colors can be applied. We stock one that works well which can be ordered. Non-stick cooking sprays such as “PAM” and fabric sprays such as “Scotch Guard” are not as effective and are not recommended as they will greatly reduce mold life.

4. Why not cast the rock molds in one step with foam resin alone; skipping the Cast Satin step? Polyurethane foams are extremely adhesive even when mold releases are used. Alone it will quickly ruin most molds after only one or just a few casts. Molds will last much longer if Cast Satin is used. Also foam does not reproduce the mold’s detail nearly as well as Cast Satin resin and the surface of foam-only castings remains soft and fragile.

5. Why do you recommend acrylic gesso as a primer for the rock castings and are there alternatives? Gesso is by far the best primer. Designed by and for artists, it is preferred because it takes color with ease, subtlety and control. It also leaves a tough and durable finish. While other white primers will work, they generally are not as good. A canned spray wall board primer named “KILZ” is a reasonable alternative and weathers better on outdoor railroads. “KILZ” is available in most hardware stores.

6. Why don’t you recommend spraying a black wash over painted castings to create the “shadows”? Spraying a black wash of paint or India ink over colored castings is a commonly used method to make the illusion of shadows in the rock casting detail. It works, but it also makes the entire casting several shades darker causing loss of control of the final color. By applying gray or black tempera over the gesso to create shadows, then adding the paint color washes, you remain in complete control of the color. No surprises.

7. Why paint the castings with thin washes of color rather than one heavier coat of paint? Thin transparent layers of color allow light to penetrate, then reflect off of the bright white gesso primer base. This gives a much more realistic illusion of reflected sunlight than can be had from opaque paints. Also, if several different colors are overlapped in layers, a much more natural rock color will result than when a single color is used.

8. Can spray can foams be used to make Geodesic Foam Scenery? They are generally not recommended because they react and harden very quickly making them very difficult to control. They are also usually much more expensive than liquid foam resins.

9. Can Geodesic Foam Scenery be used outside and with real water? GFS works great indoors or out. It is water proof and has been used in many garden railroads and indoor railroads with real water streams and ponds. Because it so light in weight it should be securely fastened down to prevent it from being moved by high winds. Indoors hot glue is the primary adhesive used to mount and bond GFS. Hot glue will soften outdoors on a hot day so a construction grade adhesive such as “Liquid Nails” is usually preferred for outside use. Waterproof paints must be used outdoors and an optional clear, flat, UV barrier over-spray can be applied to protect the color.

10. Can the resin/foam rock castings be applied over plaster hard shell or to a foam board base? Yes, the resin/foam castings can be attached to plaster, wood, foam board, “Homasote” or to almost any dry surface.

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