On Wed, 02 Feb 2005 07:36:39 -0500, DSK wrote:

Short Wave Sportfishing wrote:
I agree with Doug on the two/three coats, but I disagree with
stripping the gel coat. Stripping isn't going to improve adhesion
unless there is something that I don't understand.

It will improve adhesion over unsanded gelcoat, which isn't likely to be
the surface anyway after stripping off old bottom paint. I was just
saying that if you're putting on a barrier coat, then the gelcoat is
redundant and no great care need be taken to preserve it.

Good point.

... As for osmosis
creep past the barrier via the gel coat that hasn't been proven to be
true. There is anecdotal evidence of such a problem, but it's really
anecdotal - no laboratory evidence of blisters happening that way.

There would have to be gaps in the gel coat for that to happen. However,
the interface between the gelcoat and the glass is vulnerable to
outgassing on relatively new (less than two years) boats and if there is
already water in the laminate then this will aggravate the problem
despite barrier coat's preventing further water intrusion.

I think this explains why some boats that have been barrier-coated but
not stripped developed blisters... on warranty, no less...

That's also a good point - I hadn't considered outgassing as a
problem.

Interesting.

My own opinion is that blisters are caused by temperature differential
in marginal areas of resin thickness, but it's my own hairball theory
and not something provable.

That can explan a lot of blistering issues I've seen... I don't think
there is one single phenomenon happening with blistering.

Agreed.

Something that I did on my Contender is I used the same color barrier
coat as the bottom paint. Doesn't look to ugly when I haul it and
blast some of the crud off over the summer. :)

There's a good idea.

I have that problem on my Ranger - the bottom was barrier coated white
and the bottom paint was blue - it can be VERY ugly after a summer or
two.

Lesson learned.

Later,

Tom