Don't sand thru the gelcoat if you don't have to, Chuck. Fiberglass isn't
waterproof without it. Patch the ground out blisters with Marine Tex or
other waterproofing filler.
JIMinFL
wrote in message
ups.com...


I had a batch of chine blisters that I dealt with two or three bottom
paint jobs ago. Just sanded them flat, let them dry for a few hours,
faired them out, and slapped on the bottom paint. Cost was less than
$100. I fully expect to see those same blisters back again some day
(but maybe not)........and if I do I'll spend another $100 to deal with
them. That's much better than spending $10,000 or $20,000 or maybe more
to deal with them and *still* having them reappear in the future.

I'll never do this cuz I have waaaaaaay too many other weird projects.
It came out of a scheme of mine to measure the fluid level in oil wells
using microwaves.
I have done a lot of looking into blister repair and even have done
some of it. What I find is that blister repair is mostly a scam that
fails about 80% of the time. As others have pointed out, blisters are
really only a cosmetic problem. I have NEVER heard of osmotic blisters
causing hull failure on a boat made from woven fiberglass. I HAVE
heard of severe problems in hulls made from short strand mats. If
anybody has ever heard of a hull failure or accident resulting from
Osmotic Blisters, i'd like to hear about it.

Thanks

David

JIMinFL wrote:
Don't sand thru the gelcoat if you don't have to, Chuck. Fiberglass isn't
waterproof without it. Patch the ground out blisters with Marine Tex or
other waterproofing filler.
JIMinFL

I don't know how you would fix a blister without removing the deformed
gelcoat.

Gelcoat ( essentially a layer of tinted resin) is somewhat porous. You
may be thinking of a barrier coat, not the gelcoat. When the term
"osmotic blister" is applied, the osmosis is the passage of water
through the gelcoat, not through the laminate. Plastic doesn't absorb
water, so if there are no voids in an FRP hull it isn't ever going to
become "waterlogged".

When I refer to "fairing", that's the same process you describe above
with the filler.

Happy New Year

My thinking is backward from yours, Chuck. I think of the gel coat as the
layer that is supposed to be waterproof. The laminate may or may not be
waterproof depending on how well the layers are saturated with resin. I'm
sure if you scrape the gelcoat off something like a BayRay or other mass
produced boat, you will have a leak.
JIMinFL
wrote in message
oups.com...

JIMinFL wrote:
Don't sand thru the gelcoat if you don't have to, Chuck. Fiberglass isn't
waterproof without it. Patch the ground out blisters with Marine Tex or
other waterproofing filler.
JIMinFL

I don't know how you would fix a blister without removing the deformed
gelcoat.

Gelcoat ( essentially a layer of tinted resin) is somewhat porous. You
may be thinking of a barrier coat, not the gelcoat. When the term
"osmotic blister" is applied, the osmosis is the passage of water
through the gelcoat, not through the laminate. Plastic doesn't absorb
water, so if there are no voids in an FRP hull it isn't ever going to
become "waterlogged".

When I refer to "fairing", that's the same process you describe above
with the filler.

Happy New Year

JIMinFL wrote:
My thinking is backward from yours, Chuck. I think of the gel coat as the
layer that is supposed to be waterproof. The laminate may or may not be
waterproof depending on how well the layers are saturated with resin. I'm
sure if you scrape the gelcoat off something like a BayRay or other mass
produced boat, you will have a leak.
JIMinFL

I don't always agree with David Pascoe on some issues, but I think he
has written one of the most informative and easily understood essays on
blisters and how they affect a boat.
If you check out the illustrations and explanation at this link, you
might amend your opinion about gelcoat preventing leaks in a fiberglass
hull


http://www.yachtsurvey.com/BuyingBlisterBoat.htm

wrote in message
oups.com...

JIMinFL wrote:
My thinking is backward from yours, Chuck. I think of the gel coat as the
layer that is supposed to be waterproof. The laminate may or may not be
waterproof depending on how well the layers are saturated with resin. I'm
sure if you scrape the gelcoat off something like a BayRay or other mass
produced boat, you will have a leak.
JIMinFL

I don't always agree with David Pascoe on some issues, but I think he
has written one of the most informative and easily understood essays on
blisters and how they affect a boat.
If you check out the illustrations and explanation at this link, you
might amend your opinion about gelcoat preventing leaks in a fiberglass
hull


http://www.yachtsurvey.com/BuyingBlisterBoat.htm

I read his essay and I don't think that I said anything that needs to be
amended.
Pascoe did say that both the gelcoat and roving/mat are porous. I don't know
if this is true of modern resins but the older boats made of polyester resin
were somewhat porous. But not to the point that you would notice significant
accumulation of sea water in the bilge. I had an old Reinell once that
leaked about 2 quarts a day. It wasn't coming from the engine room nor way
forward. It had to be coming from under the cabin sole. I cut an inspection
port into the sole and found a spot where water was oozing in drop by drop
right at the center of the keel. I didn't see any cracking so I decided to
leave it as is until haulout time. After removing several coats of bottom
paint I found that the gel coat had been worn off . Probably from repeated
beachings at one time. My fix for that was a few layers of cloth and epoxy.

I would not let any crack or gouge in gelcoat go unrepaired. Particularly
under the water line.

JIMinFL wrote:


I would not let any crack or gouge in gelcoat go unrepaired. Particularly
under the water line.

I think we would agree on that. Particularly since it's almost
impossible to crack or gouge *only* the gel coat. :-)

Your experience with the leaking keel is a good example. After several
groundings, you noticed some water seeping into the bilge through the
keelson. The couple of layers and cloth you applied for a fix went well
beyond a simple gelcoat repair.

I think you could strip all the gelcoat entirely off a boat and it
would still float. If the fibers were adequately wetted out with resin,
the hull wouldn't even absorb water (or "wick" it around). That seems
to be where we disagree.

As you know, there are some premium manufacturers who don't even use
gelcoat on their fiberglass boats. If the mold is perfect enough, one
can get by with paint rather than gelcoat. Gelcoat is an easy
workaround for imperfectly finished molds, as it tends to hide various
sins while paint tends to magnify them.

wrote in message
oups.com...
Your experience with the leaking keel is a good example. After several
groundings, you noticed some water seeping into the bilge through the
keelson. The couple of layers and cloth you applied for a fix went well
beyond a simple gelcoat repair.

That isn't exactly what I said, but after removing the bottom paint, the
area sans gel coat was smooth and I didn't know if any of the laminations
had worn off. Being a belt and suspenders kind of guy, I chose to build the
area up a little. I probably could have gotten by painting the spot with
epoxy.





I think you could strip all the gelcoat entirely off a boat and it
would still float. If the fibers were adequately wetted out with resin,
the hull wouldn't even absorb water (or "wick" it around). That seems
to be where we disagree.

Now you are qualifing with "adequately wetted out with resin". Sure some
better hulls will be more resistant to water penetration. The cheaper hulls
still depend on the gel coat to keep the water out.