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Monday, May 01, 2017

Find'em and Grind'em

Dusty work this weekend, continuing to prepare the hull for the epoxy bottom treatment I'm using (Coppercoat). The boat has a mild case of osmosis - leftover chemicals from the manufacturing process react very slowly with moisture to form bubbles, or blisters, just below the surface of the hull.

At this level, in a hull an inch thick, it's pretty much cosmetic and we've happily left it for ten years. But the slow bulging of the surface can force the coating to flake and separate. Since we're going to a lot of effort and expense with the Coppercoat, it makes sense to fix as much of this as possible.

That means locating the blisters and grinding them back to solid fibreglass, then letting the hull dry out through the summer and filling them in with epoxy filler in August.

The first photo shows the white spots that reveal the blisters - white because there's a thin unbonded gap between the surface layer and the resin beneath. The black is paint that hasn't been fully sanded off yet.

In the second photo, I've ground out the blister until we are back at solid laminate, and marked each one so we know where to go with the filler later. It's a dusty job, I've got a respirator, goggles, ear muffs and look more like I belong in a Doctor Who episode.

Blisters show as white spots
Grind out each one and mark for filling

While I have the sander, grinder, scaffold and protective gear all set up, I've also been getting rid of the last of the paint around the waterline. It's slow work but finally showing a real difference. Before...and after

Before sanding the waterline

Down to bare hull

And between the sanding, usually when the rain showers came through, I moved along a couple of other looming tasks. More cleaning and scraping of the bilge area around the stern gland - this is actually getting fairly close to being paintable, even though it hardly looks that way.

And decided to go looking for the chainplates - the steelwork that holds the mast up. These are original and almost certainly in need of replacement, inspection at the very least. The bad news, well known with these older boats, is that the builders set them into the hull and completely covered them in fibreglass. 

I cut away the back of a kitchen cupboard to check on this and sure enough - there it is, a tell tale large bulge of glass fibre covering the chainplate. Well, time to research and then get busy slicing it all out. This is a tough job. 

I've found a couple of good reference sites from people who've done a similar task:


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