It sounds like you are grinding through a number of materials. If the grey material is comparatively thin, like a thick coat of paint then someone has applied either a vinylester or epoxy barrier coat on the boat during its lifespan. There were also grey polyester fillers that a lot of boat builders used to fair between the sump and the ballast keel.
More than likely the blue fibers in clear matrix is a resin rich polyester laminate which is very typical of that era. Unless the boat has had a peel and has been built back up, it is unlikely that there is epoxy anywhere in the boat''s construction.
1971 is just before the period of the worst blister prone resins. That said, the resins of that era were typically mixed with a lot of accelerator which can result in pourosity over time. In otherwords a barrier coat would be good idea.
04-05-2005 08:27 AM
hull prep question
OK, I have removed about 20 years of bottom paint from my ''71 fiberglass sloop and am down to what may be a barrier coat. It does not look like gel coat; it is grey and very hard. Where the fiberglass keel stub meets the external lead ballast there is one area where my sanding (to make the glass stump fair with the lead portion) has gone through the grey layer and revealed what looks like the lay-up: I can see blue fibers within a clear matrix; it is very hard and smooth - no fiberglass "hairs" sticking up. Could this be layup saturated with epoxy? Do I need to barrier coat this area? Should I barrier coat the whole hull, even though not even one blister of any size has turned up? Thanks for any advice.