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How To Infiltrate Zcorp Starch With Rubber


Zcorp starch can be infiltrated with various liquid rubbers (urethanes, tin or platinum-cure silicones, etc.) but they must exhibit certain specific working characteristics. Liquid RTV (room-temperature-vulcanizing) rubbers used for infiltration should have a viscosity at room temperature of 2000 cP or lower. This viscosity ensures that the liquid rubber will be fully absorbed into the starch.

CAUTION: When working with RTV Rubber, always wear nitrile or vinyl rubber gloves and eye protection. Work on a wax paper surface on top of newspaper to protect the work surface!

1. Make sure that proper proportions of 2 or 3 part liquid rubbers are measured accurately. Some manufacturers specify proportions by weight, while others indicate proportions by volume. Also, if using 3 part rubber make sure that it is mixed in the proper sequence according to manufacturer instructions.


2. If adding liquid or powder pigment to liquid rubber ensure that it is compatible with the rubber by infiltrating a sample part with the same proportion of pigment to rubber that you will use in the full-scale piece. Some pigments will inhibit the curing of the rubber. Adding too much pigment can also inhibit or lengthen cure time of liquid rubbers.


3. Rubber can be applied with a brush or with a squeeze bottle or dropper. If using a brush be very gentle with brush strokes so that surface starch isn't rubbed into the liquid rubber. This will cause a fuzzy, uneven surface texture somewhat like pills on a sweater. This can be avoided by using a gentle rolling motion with the brush. Another way to avoid this surface is to use the brush as a dropper, and use the brush to carefully drip rubber onto the surfaces of the object.


4. Start by applying the rubber to the thickest sections of the piece and the most interior, then move outward and to the thinner sections. This allows the thickest parts the most time to absorb the liquid rubber, and also allows you to find an un-infiltrated exterior part of the piece to hold onto while infiltrating the interior. If the piece allows you to infiltrate it by leaving it on the work surface that is ideal, especially if it is fragile.


5. As the liquid rubber is absorbed into the starch the surface will change from shiny to matte. Continue to apply liquid rubber to the surface as long as it continues to be absorbed into the surface and returns to a matte appearance. If any extra rubber pools on the surface after all rubber has been absorbed, (exhibiting a glossy surface), gently blot to remove it with a paper towel. If the surface is over-infiltrated it will make the surface irregular and uneven and the rubber will pool in an unattractive mass on the work surface around the piece.


6. Allow the piece to cure undisturbed at room temperature in a well-ventilated, dry place, away from any breeze that might allow dust or other particulates to stick to the surface.


7. The piece is fully cured when the surface no longer feels tacky.




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