Grind off that "lip" before you lay the new glass

Posted By: Judy B, SF Bay, P19 #266 Redwing, Catalina 27 Bijou
Date: 3/17/08 4:58p.m.

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In Response To: More keel sump questions... (pic) (amory)

I would grind the remaining edge that you chiselled right down to nothing at the bottom where it joins the sumps vertical wall. Create a wide and smooth bevel, extending upwards. The bevel should be 8-12 time the thickness of the orginal 4 layers of roving and resin that covered the wood. (The reasons: First, "hard edges" cause concentrations of stress at one point. Any time you add cloth, you should (almost) always figure out how to distribute the stress across smoth a wide area. Secondly, you will need to roll the cloth/resin with a roller to get any excess resin and air bubbles out. The laminate will be strongest if you remove as much resin as possible) I wouldn't worry about weakening the keel sump by grinding that "upper skin" down flush. The outer skin of the keel sump is probably thicker than 1/4" or 2/8" of solid glass. Just take reasonable care that you don't grind into the outer skin of the sump deeply. Make sure you confirm that the mat in the 1708 cloth is compatible with epoxy resin. Some mats have binders that will not dissolve in epoxy. Or else use a vinylester resin (a modified epoxy resin), which is much stronger and more water resistant than polyester resin. Grinding off the edge of the upper skin may resolve your worry about not having enough clearance for the nuts.... Finally, I'd ask the experts at West Systems Tech Support what "schedule" to use with epoxy resin. The instructions on the Cataliina factory drawing recommends using cloth and mat, which implies that they expected you to use polyester resin. Most mats won't wet out using epoxy resin. Fair winds, Judy B