How's my bottom look?

Pic attached. Just had bead blasted. Sorry plastic is still on, was a lunch visit as they were wrapping up. Will add an wrap off picture at my next day visit.

Verdict by Dave was: Lots of little "blisters", no big ones. A bottom coat every once in a while would have avoided this. Fill and sand and paint was his recommendation, he made it sound easy, I'm sure it's not.

This is the result of about 10 years of sitting in the Hudson.


Your thoughts on the condition and next steps? I will consult the yard on Monday also.

bridaus said:

How's my bottom look?

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Turn around and let's have a look. I'd say a few thousand lighter on one side, but your boat is going to move through the water like a hot knife through butter.

I should add that none appear to pierce the laminate.

bridaus said:

I should add that none appear to pierce the laminate.

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OK, getting serious now.

Are you considering an epoxy barrier coat before antifouling? I've never done barrier coating but hear it's really good at helping stop osmossis and blistering. It's also supposed to help hold the antifouling better.

Interprotect 2000 is your friend. Call Interlux and they will tell you how many gallons to put on. Do not scrimp on it, use however many gallons they say to. Keep putting on the paint until you run out. Then bottom paint. Be careful as to when to put the next coat on. If you wait too long you will have to sand before the next coat. Do the thumbprint test to determine when to put the next coat on.

I figured barrier coat and bottom paint for sure. I feel like these are depressions, but it's very hard to feel them (they are not deep). Will an Interlux "paint" fill those? In other words is there a "filling" and sanding step, or is a lot of coats of special products going to work?

Left the above, but read the application guide, it says "no sand"... hmm.

Edit: But the application instructions seem to imply good gelcoat underneath. I'm not sure I have that. I'm uploading more pics here shortly.

More pics

ben2go said:

Turn around and let's have a look. I'd say a few thousand lighter on one side, but your boat is going to move through the water like a hot knife through butter.

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If that's a wallet joke, I do not appreciate it...

Also, I don't think anyone's ever said that about a KK... "hot knife/butter".

the best way is spray on 2000, if not roll with small nap



then 3 ' long board sanding


Not for everyone, I did it, do about 1/4 a day



Then sprayed the bottom paint was like a babies ass


the boat's speed increased dramatically.


Had friend sand his with air powered DA, not as good but nice

Yeah, lots of opinions on blisters and little knowedge on the net.


After I ground through 1/2 inch of hydrolyzed laminates in a 6x6 foot section after grinding off the gel coat (only the start of figuring out which hiuls are destined to bad things)...I did about 8 months of research on fiberglass deterioration....and what to do about it.



There is little correct info in the boating world on it. I found much more science in the underground tank and piping industry that had a lot more to lose. And I followed their research.


If your gelcoat is full of tiny pinholes and wormlike voids.....taking the gelcoat off and investigating laminate separation is a good idea.


Can't repair what one misunderstands.

bridaus said:

If that's a wallet joke, I do not appreciate it...

Also, I don't think anyone's ever said that about a KK... "hot knife/butter".

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One other thing: At no time did I observe a "blister" in the sense that I never saw a bubble or anything with a dome/circular shape. The paint simply looked bad/non uniform in color. The hull everywhere was flat with no protrusions/bubbles or lumps.

After blasting, you see the results, it all feels very flat, just looks the way it does. No water or smelly bubbles or anything came out at any time.

I'm not saying I know therefore that there were no blisters, only that pictures of what I've seen during my research are not the same as what I am seeing, causing me to ask questions. I will get the yard opinion on Monday, but I like to correlate/corroborate information.

If they are just tiny little pinholes and do not extend into the layup then I would just take some thickened Interlux 2000 and fill the pinholes as you are doing the epoxy barrier coatings. A professional that did bottom painting told me about that trick when I had that same issue with a Trojan F32. I put on a coat for 2000 and let it set up almost where it was ready for the next coat and then took some of the 2000 that was starting to go off and was thicker and used a spreader to fill the pinholes. I could not get to all of them in one pass so I would hit some between coats 1 and 2 and some more between coats 2 and 3 and so on. It worked fine and 5 years later the current owner says it is still in good shape without any blisters.

This is my experience with blisters. I have never done this on a boat that has sat in the water more than a summer and never on a large boat. I guess fiberglass is fiberglass no matter the boat size. On a tri-hull, cathedral hull if you prefer, I ground the blisters out and filled the divots with epoxy and silica mixed to a peanut butter consistency. Sanded the entire hull and painted with a good marine paint the old roll and tip way. Of course, I would do it differently on a large liveaboard boat that could see years between haul outs.

During survey haul-out we saw some nickle sized blisters on the bottom - not all over, but several. Will be hauling out in a few weeks to 'do the bottom' and some other work - new toilets/hoses... I plan to first grind out those blisters and let them drain/dry for the month I plan to be on the hard, then fill the holes and paint - barrier and bottom pain.

The pinholes can be a true danger sign that you have serious hydrolyzing of the mat and rovings..serious hydrolysis can occur with no blisters.


90 or so percent of what is written on the internet about bottoms (blisters, etc) I found out was mostly incorrect.


I spent at least 6 months of intense research and made numerous phone calls around the country talking with yards with lots of experience in total bottom jobs. They have a completely different view of most of the stuff you read or hear on the docks.

I’d paint it and put it back in the water. Bottom jobs have a tendency for major project creep. Without proper drying of the hull, putting a barrier coat on is waste of money imho. Save the investigation for another time. Summers here!

Larry M said:

I’d paint it and put it back in the water. Bottom jobs have a tendency for major project creep. Without proper drying of the hull, putting a barrier coat on is waste of money imho. Save the investigation for another time. Summers here!

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oh how true.....


Boats usually don't fall apart suddenly anyway...but the "ostrich - don't worry about the bottom because it's only blisters" apparoch I don't recommend forever.

Boat is staying on hard until next summer for all my other projects.

Knowing this, yard says let it dry until next spring and then epoxy fill/barrier, paint it and use the heck out of it.

It won't dry well/fast enough unless you take the gel coat off. Some even say you have to grind or peel to dry to be sure.


I found sopping wet laminate after the boat had been hauled for 7 months where there was still gel or bad laminate.


Vacuum with heat is one method to hasten it.

A "bottom job" on a wet hull can be worse than none at all....at least according to the more knowledgeable in my research.

Even water in the bilge can contribute to hydrolysis and hull issues.

Bottom from hell

Myself and two other friends bought a sailboat to race that had sat at a dock on Dog River Alabama for seven years. There was mangroves growing out of giant teacup barnacles on the port side. We worried about the EPA when we hauled the boat out of there. We let it sit and dry for six months then started by blasting it smooth so to speak. Needles to say there was a whole lot of everything going on, blisters, pin holes, you name it we had it. An old fiberglass boat builder told us after we got everything cleaned up to use Marine Tek on any and all depressions, holes, etc. We faired that haul with Marine Tek and a random orbital sanders to a fine finish then sealed the the deal with 3 coats of Interprotect Epoxy. Finally a couple of coats of hard bottom paint. That boat today is still racing on Mobile Bay and the bottom is still perfect.

psneeld said:

Yeah, lots of opinions on blisters and little knowedge on the net.

There is little correct info in the boating world on it. I found much more science in the underground tank and piping industry that had a lot more to lose. And I followed their research.

Click to expand...

Agreed, reams of disinformation and misinformation where osmotic blistering is concerned. The USCG commissioned a detailed study by Doctors Thomas Rockett and Vincent Rose, Phd's both, of the Univ of Rhode Island...in 1987, it answered virtually every question there was about what causes osmosis, as well as how to prevent it. And yet, the marine industry keeps trying to reinvent this wheel. The hot tub industry dealt with these issues long before we did, and they too figured it out.

In short, boats don't usually sink form osmotic blisters, but depending on their size and number, blisters can weaken a laminate's structure, which could be relevant in the event of a grounding or other stress.

There are two approaches, one, grind, fill and fair blisters, than apply an epoxy barrier/primer coat (the value of barrier coating a "wet" laminate is debatable, but you do need a primer, the only difference between Interprotect 2000 as a barrier vs. a primer is the coat thickness), and bottom paint, this is purely cosmetic, and will not prevent future blisters from occurring, which may be an issue when the vessel is sold. It will typically cost $3,000-$5,000, depending on the size of the vessel, yard location, time of year etc.

Two, patch test the vessel's bottom to determine the depth of affected laminate, peel the affected laminate off, re-laminate with vinyl-ester resin, fair, apply epoxy primer and bottom paint. If done correctly this is a permanent fix, blisters will not re-occur. The cost is $10,000-$20,000 depending on the size of the vessel, yard location, time of year etc. There aren't many yards who have the skill level to do this, and this repair should come with a 10 year warranty.

There is no such thing as drying a "wet" bottom, please don't allow anyone to do this, it is a waste of time and money.

For a full discussion on the subject, see Part I
http://stevedmarineconsulting.com/wp-content/uploads/2014/03/Blistology-Pt-1-PMM-Jul_Aug-06.pdf and Part II https://stevedmarineconsulting.com/wp-content/uploads/2014/03/Blistology-Pt-2-PMM-Jul_Aug-06.pdf

My 78 Grand Banks went through this last winter. Too many blisters & delamination.
Shaved the bottom. Yup-shaved....
Glass under the gel was solid.
Sand & faired bottom.
Total Boat, Jamestown Distributors, vinylester resin.
Reglass, 3 layers of glass matting
Sand seams
8 coats of Iterprotect
Bottom paint
New boot stripe painted
Bottom is harder than concrete when you tap it
Good for another 40 years!

Have a number of pictures if you want to see before/after

I don't know much about bottoms but learning as you are. However, i think your boat is awesome and was wondering if you would give us a tour of it? Does it have wheel house or not? Thank you for your time...

fsarcone said:

My 78 Grand Banks went through this last winter. Too many blisters & delamination.
Shaved the bottom. Yup-shaved....
Glass under the gel was solid.
Sand & faired bottom.
Total Boat, Jamestown Distributors, vinylester resin.
Reglass, 3 layers of glass matting
Sand seams
8 coats of Iterprotect
Bottom paint
New boot stripe painted
Bottom is harder than concrete when you tap it
Good for another 40 years!

Have a number of pictures if you want to see before/after

Click to expand...

Really warms my heart to hear about this being done correctly, and that there are yards who understand how to do this properly. I'm curious, did they give you a warranty?

For every one of these, sadly, there are three "at the direction of the yard we had them sand off the gelcoat, tented the bottom and placed heaters/dehumidifiers inside, dried the bottom, then barrier coated and bottom painted" stories.

You can do that but don't expect lasting results or value for your money, and thus it makes more sense to simply grind and fill blisters individually, a cosmetic only, economy repair, with no resistance to future blisters, or go the whole 9 yards and do it properly for a permanent, but admittedly more costly, fix.

What irks me is when yards lead owners to believe that bottom "drying" is a long-term solution, when it's no solution at all, there is absolutely no science behind it what so ever. The article I shared earlier explains why.

Steve DAntonio said:

Agreed, reams of disinformation and misinformation where osmotic blistering is concerned. The USCG commissioned a detailed study by Doctors Thomas Rockett and Vincent Rose, Phd's both, of the Univ of Rhode Island...in 1987, it answered virtually every question there was about what causes osmosis, as well as how to prevent it. And yet, the marine industry keeps trying to reinvent this wheel. The hot tub industry dealt with these issues long before we did, and they too figured it out.

In short, boats don't usually sink form osmotic blisters, but depending on their size and number, blisters can weaken a laminate's structure, which could be relevant in the event of a grounding or other stress.

There are two approaches, one, grind, fill and fair blisters, than apply an epoxy barrier/primer coat (the value of barrier coating a "wet" laminate is debatable, but you do need a primer, the only difference between Interprotect 2000 as a barrier vs. a primer is the coat thickness), and bottom paint, this is purely cosmetic, and will not prevent future blisters from occurring, which may be an issue when the vessel is sold. It will typically cost $3,000-$5,000, depending on the size of the vessel, yard location, time of year etc.

Two, patch test the vessel's bottom to determine the depth of affected laminate, peel the affected laminate off, re-laminate with vinyl-ester resin, fair, apply epoxy primer and bottom paint. If done correctly this is a permanent fix, blisters will not re-occur. The cost is $10,000-$20,000 depending on the size of the vessel, yard location, time of year etc. There aren't many yards who have the skill level to do this, and this repair should come with a 10 year warranty.

There is no such thing as drying a "wet" bottom, please don't allow anyone to do this, it is a waste of time and money.

For a full discussion on the subject, see Part I
http://stevedmarineconsulting.com/wp-content/uploads/2014/03/Blistology-Pt-1-PMM-Jul_Aug-06.pdf and Part II https://stevedmarineconsulting.com/wp-content/uploads/2014/03/Blistology-Pt-2-PMM-Jul_Aug-06.pdf

Click to expand...

Steve I know you are the expert here but I beg to differ with your statement about drying the hull. In 1986 I bought a 1974 Ericson 32 with blisters in every square foot. Blisters were so common I figured I'd buy the boat cheap and put the work into it. We hauled it, ground off all of the gelcoat, ground out the blisters, bagged it in plastic down to the ground, and put two dehydrating units inside. The flow of water out of them continued for quite some time. Periodically, with the help of the yard, we would use a moisture meter on the hull. It took from early February to late April before the moisture meter stabilized at its lowest number and the river of water out of the dehydrators diminished to a tiny trickle. Then we used West System epoxy thickened with micro-balloons to fair the divits from the blisters. We were not artists so we did at least two tries over the whole bottom and rudder. Then six coats of West System epoxy. Two coats in a day, then a day of sanding and one of two coats till done. Two coats of bottom paint. When we put her in the water, she floated amazingly high in the water without all the weight she had been carrying. No blisters for 12 years. Then, one to three at each successive haul out. Being in California, we would haul every two years for bottom paint.

Just to add to the info here, my current boat had very small blisters (about 1/2 the size of a dime). I had the bottom sandblasted and a moisture run over the bottom (no or very little moisture was found). Three coats of Interprotect and two coats of bottom paint and three years later, no blisters. Perhaps dumb luck and hopefully it continues.

I’m sure there may be many ways to correct the problem of blisters. I’ve followed Steve for years and I will always respect and value his opinion.

bridaus said:

One other thing: At no time did I observe a "blister" in the sense that I never saw a bubble or anything with a dome/circular shape. The paint simply looked bad/non uniform in color. The hull everywhere was flat with no protrusions/bubbles or lumps.

After blasting, you see the results, it all feels very flat, just looks the way it does. No water or smelly bubbles or anything came out at any time.

I'm not saying I know therefore that there were no blisters, only that pictures of what I've seen during my research are not the same as what I am seeing, causing me to ask questions. I will get the yard opinion on Monday, but I like to correlate/corroborate information.

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You have your own observations, and "Dave`s advice". Who is Dave,? the blast operator, if so he`ll have seen lots of bottoms in various states of disrepair. Your description is not, in my limited experience, typical of osmosis. There are usually blisters with a nasty vinegary watery discharge when you put a metal object, like a bradawl,into them. You don`t have that, you don`t even have blisters. Blisters are best seen just after hauling while the hull is still wet,looking along the hull often helps but it can be a lot more obvious.
Wait for the Yard`s opinion. To me it sounds ok,conservative fill and paint could be indicated, but that may be just my limited experience. There are so many opinions about osmosis/hull degradation it`s hard to know, but your situation doesn`t sound pressing or urgent,to me.

RickyD said:

Steve I know you are the expert here but I beg to differ with your statement about drying the hull. In 1986 I bought a 1974 Ericson 32 with blisters in every square foot. Blisters were so common I figured I'd buy the boat cheap and put the work into it. We hauled it, ground off all of the gelcoat, ground out the blisters, bagged it in plastic down to the ground, and put two dehydrating units inside. The flow of water out of them continued for quite some time. Periodically, with the help of the yard, we would use a moisture meter on the hull. It took from early February to late April before the moisture meter stabilized at its lowest number and the river of water out of the dehydrators diminished to a tiny trickle. Then we used West System epoxy thickened with micro-balloons to fair the divits from the blisters. We were not artists so we did at least two tries over the whole bottom and rudder. Then six coats of West System epoxy. Two coats in a day, then a day of sanding and one of two coats till done. Two coats of bottom paint. When we put her in the water, she floated amazingly high in the water without all the weight she had been carrying. No blisters for 12 years. Then, one to three at each successive haul out. Being in California, we would haul every two years for bottom paint.

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Ricky, I'm not doubting what you've relayed, and the fact that you've had no blisters in 12 years is good news, but...

Moisture meters are designed to read water, not acetic acid and glycol, two of the byproducts of osmosis. The acetic acid is what provides the vinegar odor when bursting osmotic blisters.

(Water penetrates laminate and interacts with water soluble materials, typically starch binding agents used to hold fiberglass fabric together, as well as binding agents, used to promote binding between resin and glass. The acid attacks the resin, leaving behind "fiber whiting' areas where resin has been dissolved, it's often visible when peeling a bottom. Those resin-starved areas do reduce laminate stiffness).

This is why the "drying" approach is so misleading, moisture meter readings may actually fall, but acetic acid and glycol content remain, they do not evaporate at atmospheric pressure/temp (there is a company in the UK that markets a product called HotVac, which applies heat and vacuum to bottoms in an attempt to overcome this phenomenon, the problem is it's difficult to measure its success because there is no reliable way to easily read acetic acid and glycol content of a laminate).

As for the boat floating higher after the moisture removal (and after adding all that epoxy), it is scientifically impossible for this to be the case. The volume of water solid fiberglass laminate can retain is in fact quite small, a reading of 100 on the Tramex moisture meter relative scale is a scant 1.5% moisture by weight. So even a completely saturated hull is in fact retaining very little water. When peeling "saturated" laminate, it feels dry, there's no discernible moisture.

The "rivers of water" that issued forth from the dehumidifiers was almost certainly from the air surrounding the boat, not the laminate, and the fact that they stopped was likely a result of a seasonal weather change. Again, it's impossible for solid laminate to hold this volume of water.

Having said all that, the fact that you've had few blisters since the repair is cause for celebration.

As an aside, using epoxy to laminate a bottom is user friendly in the respect that it is low VOC, i.e. it doesn't smell. However, there's a price to be paid, it is very time consuming and energy intensive to fair. Few professionals use this approach, they use vinyl-ester resin for laminating (which is hydrolysis proof), and a VE fairing compound, which is easy to sand and fair.

Bigsfish said:

Just to add to the info here, my current boat had very small blisters (about 1/2 the size of a dime). I had the bottom sandblasted and a moisture run over the bottom (no or very little moisture was found). Three coats of Interprotect and two coats of bottom paint and three years later, no blisters. Perhaps dumb luck and hopefully it continues.

I’m sure there may be many ways to correct the problem of blisters. I’ve followed Steve for years and I will always respect and value his opinion.

Click to expand...

Indeed, there are several approaches to blister repair, but in the vast majority of cases, where a yard proposes taking your money in return for a "solution" whose likelihood of success is very low, then boat owners should be suspicious.

A cheap fix, grinding, filling and fairing, with no guarantee of re-occurrence may be deemed worth the trouble, and in some cases I've even agreed this makes sense where the value of the vessel or the budget didn't support the a permanent repair. If you seek a permanent solution, with a warranty, then peeling and re-laminating is the only one I know of that is guaranteed to work.

By the way, you can have no blisters on a bottom that reads wet using a moisture meter. The presence of moisture does not necessarily go hand in hand with hydrolysis and blister formation. Osmotic blisters form when water interacts with water soluble materials in the laminate. If those materials are not present, blisters will not form. Of course if water cannot penetrate the laminate, then that too will prevent blisters, this is why many builders today "skin-coat" their bottoms using two layers of VE resin and fabric (an effective osmosis resistant skin coat must be a minimum of 1/10 of an inch thick, it has to include fabric, you can't simply paint on VE resin), or build the whole hull using VE resin (it's more expensive). It's why few new boats develop blisters and most new boats come with hull warranties that include blisters.

I was at the Grand Banks/Palm Beach yard recently in Malaysia, they build the whole boat using VE resin, it's blister proof and and better than polyester all around, more epoxy-like for stiffness and elongation characteristics.

You can also use an epoxy barrier coat, however, their lifespan is technically finite, Interprotect 2000e claims 10 years, after which it should be renewed. Whether that's science or warranty protection I'm not sure. The epoxy barrier does make an excellent primer for application of anti-fouling paint, as you can achieve a chemical bond between the two if you apply within the established application window. I consider it a prerequisite even on VE bottoms, albeit with fewer coats needed as it's a primer and not a barrier. More on that subject here https://www.proboat.com/2015/08/antifouling-tactics/