Builders' Forum Archives
Posted by leeG on Aug 29, 2004
Nothing like the voice of experience. The product descriptions says this:
"SilverTip Epoxy Resin is designed for use where strength, appearance and workability are paramount. This resin cures to a brilliant, colorless film that will not blush even with a fast hardener."
On a related issue of cure times for MAS slow cure some folks might get the impression that it's ready to sand or remove clamps in 24hrs as there are ambiguous directions related to that time designation for "curing". Anyone who's removed clamps on hatches,coamings, or coamings in 24hrs at "room temperature" and had things come apart has learned that full cure for use or sanding is different than cured enough for handling. Ditto for sanding little balls of soft epoxy on seemingly cured epoxy. It's worth going to the MAS site and seeing that it takes 5 days for a "full cure" at 77 degrees and 7.5 days at 68 degrees. My experience has been that you can remove clamps in a little more than 1/2 the full cure time for joints that are held in tension or scarf joints where the joint has to be as strong as the wood like sheerclamps/rubrails. But that time is not sufficient for sanding even though the epoxy appears hard it can ball up when sanded, so 7 days for full cure at "room temperature" might be necessary for sanding.
"Most marine epoxy is intended for use at room temperature, about 72 degrees. A rule of thumb we use at CLC is that cure time roughly doubles with each 10 degree drop in temperature. Epoxy that cured in 24 hours this summer will take 48 hours at 60 degrees, 4 days at 50 degrees, and so on. The best epoxy working scenario is a heated shop, even if you heat the space only for the duration of the project. If keeping your shop at 70 degrees is not an option, you're probably going to need to speed up your epoxy. All CLC boat kits come with a two-part MAS Epoxy system. The default hardener for the epoxy in the kits is MAS "Slow", which yields a 24 hour cure at around 75 degrees. MAS Slow is perfect for stitch-and-glue boatbuilding work because it has a long "pot life" and, best of all, does not "blush" as it cures. " Not everyone lives in the same "room" temperature and not every "room" maintains a constant temperature so don't rely on precise numbers like 24hrs without precise temperatures held for a constant 24hrs. I'd rely on a constant 90degree temp before taking clamps off in 24hrs with MAS slow cure. Using lamps to raise the temp on a joint can certainly work,,like a hatch rib,,but the entire area has to be 90degrees,,if one part of the hatch is sitting at 70degrees because the lamp isn't shining on it then that rib might not hold if removed in "24 Hours".
In Response to: silvertip blush warning by DaveW on Aug 29, 2004