Fill coats?

Hey all.  I have a question regarding the fill coats on a sh17 build. Are you supposed to fill the weave on the hull glass before or after you put the deck glass on?  The instructions seem to direct you do it before but it makes more sense to me to do the fill coats once all of the glass is on the exterior.  What did you guys do and how did it turn out? Thanks   

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RE: Fill coats?

I built 2 Shearwater hybrids. On my first one, I filled the hull weave first. On my second, I didn't. Both turned out well. Biggest difference? Build time for the 2nd was 120 hrs vs 160 for the first. Probably saved a few of those hours right there.

Someone else may chime in with good reasons for doing it the other way.

Cheers, Pat

RE: Fill coats?

I just finished putting the deck glass on a couple of Chesapeakes, and would do it differently next time:

Wet out the hull glass with a squeegee (thoroughly squeegeeing off and disposing of all excess resin), and then a few hours later roll and tip a second coat to partly fill the weave. Let that cure, and do the same with the deck. Let that cure, sand any glass overlap areas fair, and then lightly sand the hull and roll and tip two more thin coats a few hours apart. Let that cure, and do the same thing for the deck. Let that cure, and thoroughly sand the entire boat in preparation for varnishing and painting. There doesn't seem to be any advantage to getting the hull ready for painting, and then overlap the top edge of it with new fiberglass.


RE: Fill coats?

Thanks for the input guys. I'm gonna go ahead and put the deck glass on before the final fill coats.


RE: Fill coats?

I would just sand about the upper 2" of the hull glass before putting on the deck glass, to get a good mechanical bond where they overlap.

I think the main reason for putting all the fill coats on the hull (or the deck) one right after another is to save time: no waiting for cures between coats. It also gives a chemical bond between all coats, but I'm not sure that that's really important. I've been told that the strength is in the wet out coat, and anything after that is just to get a smooth surface, and for some abrasion resistance.

My surfaces are always quite rough after the wet out coat and one fill coat, so I like to let it cure and carefully sand it, without unintentionally sanding into the glass. Then the last two thin rolled on coats go on smoothly, and any places where the glass was slightly exposed get a smooth covering of two full coats, before the final sanding before paint or varnish.


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