Bottom Job Process/Materials Recommendations

[SVTwilight]

Have a new to me boat prospect located in S FL. Haul and survey shows some blistering. Doesn't appear to be much past the gel coat. Boat does not currently have epoxy barrier coat on it.

Not had to deal with much blistering up here on Cape Cod, so looking for advice from those with more real life experience.

From what I am reading, after hauling, peeling, removing and fairing blisters and drying the hull, I find a variation in the number of coats of Epoxy applied and even the number of coats of bottom paint after that.

Going to be using the boat on the US East coast and Caribbean.

Also, are any of the epoxy barrier formulas better than others?

Is scrape and fill ok, or is soda blasting really a better option?

Thanks in advance....

[Cheechako]

It's a highly debatable subject. Peeling can be very expensive by the time it's all done. But a more sure way of ending the problem if it's severe. I am a big believer in using actual epoxy resin as a barrier coat. Many pros want to use epoxy paint offered by suppliers though. I have successfully ground, filled and barrier coated with resin on two boats. I have had one boat that was "grind and fill" on prior to my ownership and it was a problem after a year or so. There was no resin on that boat, but it's debatable what barrier there was also. You must give it time to dry out, which means find a yard that allows long term storage without exorbitant fees. There are ways to accelerate the drying.
Some boats have thousands of tiny BB size blisters, these are often shallow. For bigger blisters it depends; everywhere? just one area? Quarter size or less? For shallow moisture, an expert with a disc grinder can clear off the gel for drying a lot cheaper than peeling and fairing.
Also, check under your floorboards for blisters inside the hull. I've seen one. That boat would be so wet I doubt peeling would be a good cost expenditure.... you might as well fill and grind, coat and go sailing.

[Suijin]

It all comes down to what you mean by "some" blistering. Are we talking 5-10 blisters on each side, or 50?

If the boat does not have barrier coat on it, that would well explain the blisters. Actual peeling, with a machine, may well be total overkill for what you're looking at. To be clear, "peeling" involves taking off the gelcoat and some thickness of layup, and basically then giving the boat a new bottom. It's a HUGE project. VERY expensive.

If the boat just as a few blisters, here is what I would do:

- Scrape all the old paint off with carbide scrapers. You can have it soda blasted, but that is expensive and it leaves the surface pretty rough. Scraping is generally faster than sanding although you can test which is faster for the build up that you've got.

- Repair and fair. Below the waterline, grind out any blisters down to good glass, fill with thickened fairing epoxy, sand fair.

- Wash and, if you're feeling frisky, solvent wipe.

- Put on one coat of barrier coat and let it cure. Now you'll be able to see the state of the bottom much more clearly; imperfections will be easier to spot. Repeat fill and fairing with epoxy.

- Sand with 100 grit for tooth.

- Apply at least three more coats of barrier coat. Now is not the time to skimp. You don't want to do this again. The more coats the better the projection. Some people put 8 on.

- Apply your anti-fouling. If possible, apply while the last coat of barrier is still hot, which will create a chemical vs. physical bond.

Sherwin-Williams makes a commercial marine barrier coat that is less the 50% the prices of the Interlux and Pettit products. That said, the last coat of barrier should be the same brand as whatever anti-fouling you're going to put on for the best possible bond.

If I were you I'd go with Pettit Trinidad anti-fouling, if starting fresh. It's so superior (IMHO) to any ablative it's not even funny. Three coats, plus a fourth on leading edges and the waterline.

[Shrew]

If it were my boat, I would have it soda blasted. I would use the barrier coat based on the manufacturer recommendations of the paint I was using. I would apply both the barrier coat and paint as per the manufacturers recommendations for the barrier coat and paint I chose.

[SVTwilight]

Originally Posted by Suijin

It all comes down to what you mean by "some" blistering. Are we talking 5-10 blisters on each side, or 50?

If the boat does not have barrier coat on it, that would well explain the blisters. Actual peeling, with a machine, may well be total overkill for what you're looking at. To be clear, "peeling" involves taking off the gelcoat and some thickness of layup, and basically then giving the boat a new bottom. It's a HUGE project. VERY expensive.

If the boat just as a few blisters, here is what I would do:

- Scrape all the old paint off with carbide scrapers. You can have it soda blasted, but that is expensive and it leaves the surface pretty rough. Scraping is generally faster than sanding although you can test which is faster for the build up that you've got.

- Repair and fair. Below the waterline, grind out any blisters down to good glass, fill with thickened fairing epoxy, sand fair.

- Wash and, if you're feeling frisky, solvent wipe.

- Put on one coat of barrier coat and let it cure. Now you'll be able to see the state of the bottom much more clearly; imperfections will be easier to spot. Repeat fill and fairing with epoxy.

- Sand with 100 grit for tooth.

- Apply at least three more coats of barrier coat. Now is not the time to skimp. You don't want to do this again. The more coats the better the projection. Some people put 8 on.

- Apply your anti-fouling. If possible, apply while the last coat of barrier is still hot, which will create a chemical vs. physical bond.

Sherwin-Williams makes a commercial marine barrier coat that is less the 50% the prices of the Interlux and Pettit products. That said, the last coat of barrier should be the same brand as whatever anti-fouling you're going to put on for the best possible bond.

If I were you I'd go with Pettit Trinidad anti-fouling, if starting fresh. It's so superior (IMHO) to any ablative it's not even funny. Three coats, plus a fourth on leading edges and the waterline.

Thanks for the thoughtful replies all. The boat had dozens of nickel to quarter sized blisters and a few that were baseball sized. Some BB blisters along the waterline. After a couple of hours in the slings, most of the coin sized blisters disappeared, but they probably were across 20-30% of the hull. I took photos, but the bottom paint is black, so they really don't show up in a meaningful way.

Humorously, the locals down in FLL just shrug and say blisters are a way of life there. Perhaps for some, but I don't think I would care to live with that on my boat.

I am warming up to the soda blast / peel and epoxy resins ideas, but I imagine that in general the cost scale of this will lead us to look for other boats where the owner has already done this. The boat is excellent otherwise and it is really surprising to me that the current owner didn't take car of the bottom during a lengthy refit a few years ago.

[SVTwilight]

Originally Posted by Cheechako

It's a highly debatable subject. Peeling can be very expensive by the time it's all done. But a more sure way of ending the problem if it's severe. I am a big believer in using actual epoxy resin as a barrier coat. Many pros want to use epoxy paint offered by suppliers though. I have successfully ground, filled and barrier coated with resin on two boats. I have had one boat that was "grind and fill" on prior to my ownership and it was a problem after a year or so. There was no resin on that boat, but it's debatable what barrier there was also. You must give it time to dry out, which means find a yard that allows long term storage without exorbitant fees. There are ways to accelerate the drying.
Some boats have thousands of tiny BB size blisters, these are often shallow. For bigger blisters it depends; everywhere? just one area? Quarter size or less? For shallow moisture, an expert with a disc grinder can clear off the gel for drying a lot cheaper than peeling and fairing.
Also, check under your floorboards for blisters inside the hull. I've seen one. That boat would be so wet I doubt peeling would be a good cost expenditure.... you might as well fill and grind, coat and go sailing.

Cheechako, out of curiosity, on the Epoxy application, how thick and how many coats did you go?

[Suijin]

Originally Posted by SVTwilight

I am warming up to the soda blast / peel and epoxy resins ideas, but I imagine that in general the cost scale of this will lead us to look for other boats where the owner has already done this.

As soon as you go the peeling route, you're looking at mucho cake to get it done. Essentially, the whole bottom, after it's been peeled, needs to be reglassed/gelcoated/encapsulated and made fair. Think hundreds of hours of labor.

Again, dozens of blisters might not be too bad. It's really a question of how much moisture permeation there is and if there is any resulting delam of the layup. It could be largely cosmetic, it could be more serious. A good surveyor could provide some more information on that, and if there's a price adjustment to be had based on his findings, you could come out ahead. The question becomes do you want to make an offer, and pay for the survey, and be willing to walk away if the findings are unacceptable.

[a64pilot]

That many and big as baseballs, I'd walk.
My boat had just had a barrier coat put on it a year before I bought it, the survey we found clusters of 1/4" bubbles, call them pox, baby blisters just in the gelcoat.
Two years later and they are gone. I did nothing to them.
I'm real sure it wasn't allowed enough time to dry out and the barrier coat trapped the moisture in the hull, eventually it dissipated.
Point being you need time to let it dry before you trap water in the hull, drying time can easily be several months

[AbelCMann]

When I bought my Alberg 30 (fifty year old boat) I did not suspect blisters. There were so many coats of bottom paint on her it was hard to tell what was going on. I had the bottom soda blasted because I wanted to know her history - every scrape,gouge, thru hulls removed, repair jobs, collisions - the whole story. The soda blasting revealed all that - and hundreds of blisters. The soda blasting also opened all those blisters up, and although I had to let her dry out for months before tackling the major job of filling and fairing with epoxy resin and cabocil, then the two-part epoxy paint coat and finally the Trinidad Pro bottom paint, I have no regrets. It was a tremendous amount of work, but I sure got to know the bottom of my boat very well, and when I was done it was not only beautiful; I knew exactly what I was going to be relying upon to keep me safely afloat.

[sailorchic34]

My take on blisters after reading lots on the subject and see blisters on the old tayana 37 in florida and now on my island 34 is....... do nothing. That is for a solid glass hull with good layup blisters are a cosmetic issue. Specially the quarter size and smaller.

Gel coat is not a water barrier so over time wall can and will seep between the gel coat and layup. Those blisters disrepair rather quickly when hauled. Blistering happens more the warmer the water gets which makes Florida a prime location.

Now larger blisters that get under a layup void where the layup was not wetted out sufficiency can be a problem. Also for newer boats with a cored hull, blisters can be an issue. For a solid glass hull with good layup, no voids, blisters are strictly cosmetic and not worth the $$ to fix. I know this is opposite of what must boat yards say. Oddly I'm not at all worried. A boat never sank from blisters.

Boat yards love blisters as it's big $$$ to strip fair and coat. And guess what after spending $10k or more removing the blisters, they can and have come back.

A glass layup that was properly wetted out will not be an issue. That is there are no voids where osmosis pressure can push the water between the layups. There are fiberglass tanks that are much thinner then a boat hull that have much harsher chemicals then water inside and they pretty much never leak.

Of course that's just me and yes I'm blonde. But I'm also a fair engineer and understand much about materials.

[macman4190]

Every fall I would have a few dozen new bumps. After several years of removing them and filling with epoxy, I had the boat hauled the first week in September 2016 and pealed. November was blessed with warm weather, so the hull had some good drying time. The boatyard wants the hull moisture to be below 10%. Now they are rebuilding the bottom. Four coats of West System epoxy with barrier coat added, followed by 12-15 mils of Interprotect 2000e. Then three coats of bottom paint, the first coat being a different color from the last two coats. I will apply the last two coats, but as mentioned, this is a big time or money job.

[Geitz]

If you get the bottom soda-blasted, make sure your thru-hulls are closed. Don't ask me how I know this...................

Mike

[minaret]

Originally Posted by Geitz

If you get the bottom soda-blasted, make sure your thru-hulls are closed. Don't ask me how I know this...................

Mike

Better to stuff a rag in them. Don't wanna scratch your ball valve.

[Geitz]

Originally Posted by minaret

Better to stuff a rag in them. Don't wanna scratch your ball valve.

Good point. And stuff the rag in well so it doesn't get blown out.

[minaret]

Originally Posted by sailorchic34

My take on blisters after reading lots on the subject and see blisters on the old tayana 37 in florida and now on my island 34 is....... do nothing. That is for a solid glass hull with good layup blisters are a cosmetic issue. Specially the quarter size and smaller.

Gel coat is not a water barrier so over time wall can and will seep between the gel coat and layup. Those blisters disrepair rather quickly when hauled. Blistering happens more the warmer the water gets which makes Florida a prime location.

Now larger blisters that get under a layup void where the layup was not wetted out sufficiency can be a problem. Also for newer boats with a cored hull, blisters can be an issue. For a solid glass hull with good layup, no voids, blisters are strictly cosmetic and not worth the $$ to fix. I know this is opposite of what must boat yards say. Oddly I'm not at all worried. A boat never sank from blisters.

Boat yards love blisters as it's big $$$ to strip fair and coat. And guess what after spending $10k or more removing the blisters, they can and have come back.

A glass layup that was properly wetted out will not be an issue. That is there are no voids where osmosis pressure can push the water between the layups. There are fiberglass tanks that are much thinner then a boat hull that have much harsher chemicals then water inside and they pretty much never leak.

Of course that's just me and yes I'm blonde. But I'm also a fair engineer and understand much about materials.

Might want to read up on hydrolysis of poly resin. Blisters are an indicator of possible hydrolysis, though they can certainly exist without each other, ie hydrolysis with no blisters or blisters with no hydrolysis. While "never seen a boat sink due to blisters" is still true for me, I HAVE seen a boat landfilled due to blisters AND hydrolysis more than once.