Pin-Hole Blisters

[Doc Carter]

Just  bought a CP19, and am looking for advice for dealing with it's rather alarming degree of 'blistering' at the waterline.  Seems to be confined to the unpainted gel-coat between the anti-fouling bottom paint and the waterline tape.   

Please see photo here:  http://windsong.shutterfly.com/pictures/9   

Thoughts?

[Salty19]

Hi Doc,

First, welcome to the forum.   Great group of people here and of course nice boats too!

I don't have any advice to offer except know what these boats are no different than any other when it comes to repairing blisters.  Open google and do a search on gelcoat blister repair  to find information on how to deal with them.  Apparently the severity level dictates the method to fix them, so you may find that you need different materials and techniques than either a more minor or severe problem may require. 

With that said others here have dealt with the problem so hopefully you'll get some good advice here as well.

The good news is the CP19 is a very solid boat and should provide years (lifetime?) of service.  Fix her up right and enjoy it.

[newt]

Yep- that is the first time I have seen them on a Compac- but those are the famous osmotic blisters. Your options are Ignore them while they get bigger or peel the paint away, sand them down, fill with epoxy filler, fare hull and paint well over them. It is good to get them very dry before you do that (6 weeks at least out of the water) I did them on a Catalina- just count your blessing that they are not all over the hull like mine were.

[Doc Carter]

Agh.  Of course, it just started raining.  If only I could fit her into the garage... ;-)

[newt]

Put a tarp over her anyway Doc. Get as much moisture out of her before the freeze. When I did it on a big boat, we fired up the diesel heater inside and covered it for a couple of weeks. That helped.

[breeze]

Doc, had a lot of blisters on my 23.
From what I could see they were all small blisters. Trying to dry them from the outside will not accomplish anything.
The blisters may or may not have water in them, but as soon as the boat goes back into the water they will fill.

To fix the problem I would take a small drimmel rotary tool and grind out the bad areas, only go deep enough to remove the
damaged glass and jellcoat. Sand the affected area with a orbital sander, or vibrator to remove all wax and paint.
Wash the area with ammonia, this will stop the chemical reaction in the glass.
The next day wash with water. Let dry for a day or two, the drying time can be sped up by washing with alcohol.
Now you are ready to fill the holes.
I would paint the area that is clean using an epoxy resin like the west system. This will seal the area, and you should not have any new blisters. Note there could be some blisters deeper in the hull that could appear later.
Mix some of the epoxy resin with some cavisil to a tooth paste consistency and fill the holes using a squeegee.
Lightly sand and paint
Good Luck
David

[Doc Carter]

Hey David - Thanks for the detailed instructions!  I was planning something similar, but I really appreciate having a tried-and-true method described!

Hey, one question: Can you explain the chemistry behind the ammonia wash?  Did you figure this out yourself, or did a boat manufacturer tip you to this?

Just curious.

Thanks!

~S

[breeze]

Doc, I received the information from a local professional that repaired and painted boats.
I have used this method on several boats all with great success.
I don't know the exact reaction but after the ammonia,  the vinegar like smell is gone and the blisters will dry fast.
David

[Doc Carter]

Thanks David.  Now, I have a paint question:

The area affected is right AT the waterline.  Obviously, it has been immersed for long periods, hence the blisters (it is unpainted gelcoat!)

What kind of paint should I use though?  Bottom-paint will look like crap. ??

[curtisv]

Doc,

The kind of paint depends on how you will use the boat.  If it is trailered and spends most of the time out of the water, you could use any bottom paint.  If it is going to be on a mooring or otherwise in the water for long periods, then use an epoxy barrier coat and then bottom paint.  I won't venture into the "which bottom paint" question.

I have my boat bottom painted by Nauset Marine and they probably buy Pettit bottom paint in 55 gallon drums.  That is simply the paint they use and it costs a lot more to insist on something else.  They aren't happy because they have to deal with something else in the paint gun for one boat and then leftover paint.  It seems they set up boats in their indoor bays, scrape, mask, and spray a bunch, and then clean up the paint gun.  Makes sense.  This is probably why they keep the price down and hold your boat for a while until they have a batch to do.  Since the decision is made for me, I don't worry about which bottom paint is best.

Are you painting the bottom yourself?  If so remember that the fumes from epoxy barrier coat are not good for you so you'll need a mask and bottom paint is a bit toxic.  Probably best to use a mask for either one and best to get as little on you as you can.  I think both are carcinogens (epoxy styrene vapors are).  No sense increasing your cancer risk if you can avoid it.

Curtis