Epoxy osmosis prevention

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paulburn

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I am keen to epoxy my 10 year hull as osmosis prevention. Others have urged caution, saying you can 'trap water in' which will cause more trouble.

I am confused by this. Surely if there is moisture in the hull before one launches in Spring, then it wall always be there, regardless of whether or not there epoxy on top or not. I can understand that epoxy might delay diagnosis of osmosis (might give peace of mind !) but not that it will accelerate it.

What do others advise ?

Thanks Paul

F28r trimaran
 
Epoxy

If your boat is more than about 10-15 years old I would epoxy it. When we used to weigh race boats carefully for rating they always lost significant weight through the winter. I applied 5 coats of Awlgrip epoxy to my 1988 Sigma 38 in 1996 and it was still hard and sound when I sold it 12 years later. Hard enough to stand scraping the AF off every 4-5 years without damage. Clean off AF at haul-out, let sit till weather warms up, you need at least 10 degrees C (15C for some makes) Buy epoxy in small (0.75 or 1 litre) tins in two alternating shades and apply as thickly as you can without runs (it is fairly viscous) a coat every day and you dont need to key, put a coat of antifouling on as soon as the last coat goes off. We found 3-4" brushes better than a roller for smoothness, it is too tacky for tipping off. Don't be mean, despite the crazy price, it's not worth doing unless you are going to build up to a proper thickness. The best stuff I ever used was Hempels epoxy tar but that was more than thirty years ago and I dont think you will get the same stuff now.
BTW I clean the hull using a Bahco pull scraper, until you get used to handling it it is worth taking the corners off the blades to avoid scratching.
Usual safety stuff working around antifouling of course.
 
Quandary said:
If your boat is more than about 10-15 years old I would epoxy it. When we used to weigh race boats carefully for rating they always lost significant weight through the winter. I applied 5 coats of Awlgrip epoxy to my 1988 Sigma 38 in 1996 and it was still hard and sound when I sold it 12 years later. Hard enough to stand scraping the AF off every 4-5 years without damage. Clean off AF at haul-out, let sit till weather warms up, you need at least 10 degrees C (15C for some makes) Buy epoxy in small (0.75 or 1 litre) tins in two alternating shades and apply as thickly as you can without runs (it is fairly viscous) a coat every day and you dont need to key, put a coat of antifouling on as soon as the last coat goes off. We found 3-4" brushes better than a roller for smoothness, it is too tacky for tipping off. Don't be mean, despite the crazy price, it's not worth doing unless you are going to build up to a proper thickness. The best stuff I ever used was Hempels epoxy tar but that was more than thirty years ago and I dont think you will get the same stuff now.
BTW I clean the hull using a Bahco pull scraper, until you get used to handling it it is worth taking the corners off the blades to avoid scratching.
Usual safety stuff working around antifouling of course.
Click to expand...
I did my 30 year old boat last year, scraped off old AF with a Bosch electric scraper, then sanded and applied Blakes epoxy coating, followed with a tie coat then AF.
 
A boat ashore will dry out only very slowly during the winter unless you can put her in a heated shed. Weather is generally cold and damp, not what you want for moisture to evaporate away. If you want to epoxy, I'd suggest leaving the boat out until a moisture meter is giving satisfactory readings, probably late spring. Or sail the early part of the summer, letting her dry through mid-summer, when you might hope to get her poxed and back in for some autumn sailing.
 
My Advice

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Do nothing till you have some indication of an osmosis problem. No point in spending to prevent a problem that may not exist.

prevention is better than cure in most cases, however this does not apply to epoxy protection.

Save yourself a lot of money and see if the expenditure is woth it. A boat rhat has been treated for Osmosis will always sell for less.
 
Osmosis prevention

Every year the gel coat gets thinner below the waterline from abrasion before anti fouling, odd scratches etc. It makes sense to me to add another layer (of epoxy) to keep the barrier effective.
It would make sense to wait until the hull is as dry as possible, i.e. do it fairly shortly before launching.

A small amout of heating in the boat will help the drying process significantly.
 
Epoxy on hull

Quote Save yourself a lot of money and see if the expenditure is woth it. A boat rhat has been treated for Osmosis will always sell for less.

Bit of confusion here, the OP was asking about osmosis prevention, not about treatment. In the UK boats in the vulnerable category (manufacturer and date) are more valued if they have had effective osmosis prevention coatings applied. I would accept that buyers are put off by treatment, that is what you are trying to avoid. I would not do it on a newer boat because of the improvement in gelcoats but I did it to three in the last thirty five years and none of them have yet developed the problem, they all passed survey at time of sale with low moisture readings, (To be honest, though, I think some moisture meters are just hokum)
Oddly my new boat, 2007, came with epoxy primer under the antifouling though (except over the lead keel where it was very thick), it seemed to be thinner than a 5-6 coat job. I wonder why an experienced boat builder would waste time and money doing that?
 
lw395 said:
A small amout of heating in the boat will help the drying process significantly.
Click to expand...

It might be worth considering running a dehumidifier plumbed to drain directly overboard. This will dry the bilges as well as warm the insides by a few degrees.

Boo2
 
Last edited:
Not sure if I did the right thing, but my '79 OOD34 had a good hull survey when I bought her. Had her ashore for a bit of a restoration for 18 months. After which the hull was very low on moisture. I couldnt resist it so I sanded the bottom back to gel coat and put a few coats of blakes gelprotect SFE on. No problems to date, hopefully it was the right move...

Just in response to OLDSALTOZ, I would be surprised if my actions have de-valued the boat?!
Certainly I would have paid more for the boat had it been done already. It was a hell of a job removing 30 years of antifoul!
 
contessaman said:
Not sure if I did the right thing, but my '79 OOD34 had a good hull survey when I bought her. Had her ashore for a bit of a restoration for 18 months. After which the hull was very low on moisture. I couldnt resist it so I sanded the bottom back to gel coat and put a few coats of blakes gelprotect SFE on. No problems to date, hopefully it was the right move...

Just in response to OLDSALTOZ, I would be surprised if my actions have de-valued the boat?!
Certainly I would have paid more for the boat had it been done already. It was a hell of a job removing 30 years of antifoul!
Click to expand...

In my view preventative epoxy coat adds value. Possible exception being a boat that has always been dry-sailed.
A boat that has been peeled and epoxied because it has had boatpox is worth less than a boat that has never needed treatment imho, all else being equal.
 
lw395 said:
In my view preventative epoxy coat adds value.
Click to expand...

Hmm. I'm not sure. I think I would rather have a surface that had been properly bonded to the layup during construction, rather than one slapped on later in the hope that it sticks. That's an argument against peeling, not against a preventative coat on its own.
 
Ubergeekian said:
Hmm. I'm not sure. I think I would rather have a surface that had been properly bonded to the layup during construction, rather than one slapped on later in the hope that it sticks. That's an argument against peeling, not against a preventative coat on its own.
Click to expand...

To clarify, I meant a coating in addition to the factory gelcoat.
You'd have to fairly inept for the epoxy not to stick to the gelcoat?
 
I bought my boat in july last year, knowing that it had to coats of epoxy. One was done before she was even launched and the other ten years after that. Built in 1993. Had the survey done before purchase and not a drop of osmosis in sight, and with two coats of epoxy, theres probably more chance of me winning the lottery than this boat getting osmosis. I have no idea on cost but id highly recomend it!
 
contessaman said:
Not sure if I did the right thing, but my '79 OOD34 had a good hull survey when I bought her. Had her ashore for a bit of a restoration for 18 months. After which the hull was very low on moisture. I couldnt resist it so I sanded the bottom back to gel coat and put a few coats of blakes gelprotect SFE on. No problems to date, hopefully it was the right move...

Just in response to OLDSALTOZ, I would be surprised if my actions have de-valued the boat?!
Certainly I would have paid more for the boat had it been done already. It was a hell of a job removing 30 years of antifoul!
Click to expand...


Hi Contessaman,

I agree, it's just that some buyers will shy away if a boat has been treated, more so if by other than a professional.

Boating is a very expensive pastime and I tend to avoid spending on the 'nice to have' and go overboard to ensure any repairs are only done once.

Avagoodweekend......:)
 
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