 In every issue, we bring you the answers to real-world technical questions that have broad applications. Our technical support staff is available during normal business hours, Monday through Friday, by calling 800-321-8511 (Option 5)
Is there any information on how flat RenShape boards are from stock? Unfortunately, the manufacturer does not print a spec on the flatness tolerance. The RenShape boards are typically very flat and lay together with great precision so they can be easily glued. Our conservative guess would be +/- 0.015" over the 60" length. We need a material to cast urethane based fishing lures, as well as a suitable mold material. We would like the casting material to have a pot life of approximately 5-10 minutes and a demolding time under 30 minutes. Although we don't claim to know much about this market, many of our customers use our Bluestar V-330 Silicone Rubber to create their molds and our Freeman 1070 Urethane to create their fishing lures. As always, please read the MSDS to ensure that the urethane you use is appropriate for your application. What is the resin to fiberglass ratio for typical polyester hand layup applications? Most people end up with a mix ratio of 1 lb. Fiberglass to 3 lbs. resin or 25%:75%. If your mix is resin rich, your part will not only be weak and look bad, but there would also be heat distortion, more shrinkage, and increased styrene emissions. And the mold will have a glossy wet surface on back of mold.If your mix is resin starved, your part will have a whitish look and also will be weak, possibly leading to structural failure. A hard white buildup has accumulated on my mold - what is it? The appearance of a hard white buildup on the mold surface is commonly mistaken as evidence of styrene in the parting wax or wax buildup. The white substance is more likely styrene that has migrated from within the molds to the surface and broken through the wax barrier. Styrene molecules in the mold are attraced to styrene molecules in resins used to form the part and will bond if allowed to come in contact, causing the part to stick. Waxes are applied to mold surfaces prior to the molding process in order to prevent bonding. However, heat generated during the molding process gradually softens wax and can inhibit its effectiveness as a barrier. In order to prevent styrene migration between mold and part a polyvinyl alcohol firm (PVA) such as Partall Coverall Film or Partall Film #10 should be used in conjunction with wax. If applied properly, PVA creates a barrier through which styrene molecules cannot penetrate. Wax and/or PVA must be applied properly and adequately in order to form an effective barrier. Do you have a plastic product that would replace the old fashion fillet wax? Tuf Fil Polyester Filler can be used to create your fillets in lieu of fillet wax. See our Tuf video for a demonstration of this process. | 
