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Author Topic:   bubbling gelcoat
Ilark posted 06-15-2005 01:45 PM ET (US)   Profile for Ilark   Send Email to Ilark  
I have read many post about bubbles in the gelcoat. Is this just a cosmetic problem or is it something worse?
bsmotril posted 06-15-2005 02:57 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
It depends. You can't make a general assessment that covers all instances, but must look at each case individually. Many times, they start out as a cosmetic problem, that left neglected, causes other more significant problems. Search this site, and the internet, for "osmotic blistering" AND "Fiberglass", and you'll find much good information on causes.
Ilark posted 06-15-2005 03:29 PM ET (US)     Profile for Ilark  Send Email to Ilark     
JohnJ80 posted 06-15-2005 10:47 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
The big 'bubble' problem with gelcoat is osmotic blistering. This is where, through osmotic transfer, water becomes entrapped in bubbles in the gelcoat. This makes the hull less fair and is a bad deal. For those of us that sail, this is a huge deal and can have performance issues (fairness of hull).

Basically, you need to grind them out, let the material dry out. Reglass it and then put a sealer over the entire hull below the waterline. Very expensive.

I had a small part of my sailboat blister (1x2') The bill was $2000 to fix it.


prm1177 posted 06-18-2005 12:10 PM ET (US)     Profile for prm1177  Send Email to prm1177     
One of the reasons you see so much discussion here on the perils of osmotic blistering, is the nature of the Whaler hull. On regular, sinkable boats, the appearance of a serious blister (one where water begins to penetrate entirely through the hull) is not cause for major concern as the repairs can be dealt with both inside the hull and out. On a Whaler, the foam sandwich can make the repair more difficult and the foam itself may become waterlogged in the immediate area of the blister if repairs are left too long.

Interestingly, there is no predictable guide to blistering. All polyester resin hulls can succumb to it, but two identical boats in the water, side-by-side, may have different levels of susceptibility.

If you are planning on leaving your boat in the water for a long period of time, then you will (in all likelihood) be painting it. Use a good epoxy barrier coat as a primer (I used 4 coats of Interlux 2000e) before the antifoul paint goes on, and you should be fine.

arkwhaler posted 06-18-2005 12:18 PM ET (US)     Profile for arkwhaler  Send Email to arkwhaler     
is it harmful to leave an unpainted hull in freshwater year-round? whatabout seasonally? i know marine growth can cause performance and cosmetic issues, but what effect can continuous exposure to water have on the gelcoat and fibreglass itself?
JohnJ80 posted 06-18-2005 08:12 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
It should be fine as long as the chemical makeup of the gelcoat is such that it is not subject to blistering (the osmosis problem). If you are ok, you won't have a problem. If you are not ok, you won't know until you put it in the water for extended periods of time.

Any boat is better drysailed.


prm1177 posted 06-19-2005 02:22 PM ET (US)     Profile for prm1177  Send Email to prm1177     
A blister can form in either fresh or salt water. Theory varies on the cause, from imperfect or old catalyst in the gelcoat mix or minor voids beneath the gelcoat, to small imperfections or scratches in the hull. This is why Whaler recommends that any boat left in the water for more than 2-4 weeks at a time, have the bottom primed with an epoxy barrier coat and painted. There simply are no guarantees that a blister will not form.

Yards around SF bay charge about $1200-1500 to haul, prep, barrier prime, and bottom paint a 23 ft whaler (including materials). As JohnJ80 mentioned, this is cheaper than the cost of his repair. The peace of mind is immeasurable.

jimh posted 06-19-2005 03:04 PM ET (US)     Profile for jimh  Send Email to jimh     
Below I reproduce a section of the Boston Whaler Owner's Manual which contains specific instructions regarding bottom paint. You can find the entire manual in the REFERENCE Section of the website:

"Any boat left in salt or fresh water for more than a few days should have the gelcoat surface protected with a two-part epoxy paint followed by an anti-fouling paint. This will retard marine growth and help protect gelcoat from possible blistering. DO NOT LEAVE YOUR BOAT IN THE WATER FOR ANY EXTENDED TIME WITHOUT BOTTOM PAINT."

JohnJ80 posted 06-23-2005 10:52 AM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
I think I read somewhere that fresh water is more likely (slightly, IIRC) to blister than in salt water.

Anyhow, what can happen is that apparently the chemical concentrations of the hull can vary from spot to spot so some parts of your boat can be more prone to it than others. There really is no way to tell if the whole boat is ok or not. Since any spot has to be dried out for an extended period - this is the biggest cost in repairing the hull, leaving it in the shop with heat lamps on it for extended periods - even a small spot gets expensive.

If you leave any boat in the water for several days (except places like Lake Superior where the water is really cold), you are going to get slime and growth on the boat. So bottom paint is a good idea anyhow. Going the extra step and putting on the epoxy one time is a good idea.


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