Sandblasting hull

eastont

Chief Petty Officer
Joined
Dec 16, 2008
Messages
511
I have a few blisters in my hull and need to have them repaired over the winter. I have been told a couple of different things so I'm coming here to hopefully get some good advice.

Firstly, I was told by the marine surveyor that I had some blisters and they needed to be ground down, filled in and have interprotect etc. re-applied over the winter.

Then during this past summer in talking to many boating experts (dock talkers) I have been told the best way is to sandblast the whole hull down to the gelcoat and let it dry over the winter and then have interprotect etc applied.

My wonder is thus, to do just the blisters costs around $2-$3,000..to do the complete hull has been quoted up to $8,000.

Any experts and I mean real experts, know anything about this?

Thanks
 

ondarvr

Supreme Mariner
Joined
Apr 6, 2005
Messages
11,527
Re: Sandblasting hull

Sand blasting doesn't work that well, it can very difficult to control the depth when removing material. Also just removing the gel coat doesn't help much, blisters are typically in the laminate, so you need to remove the laminate down to where it is no longer affected by the water. And it's an all or nothing project, half way attempts at fixing them typically only hold up a short time.

Gel coat peelers are used to remove gel coat and glass somewhat evenly so there is less fairing needed to get it looking good again.

To do it correctly for long lasting success you need to remove all of the gel coat, plus all of the laminate down to a level where there are no more blisters, not just dig out the visible ones. Then, depending on how much laminate was removed the hull may need to be built back up to its original thickness with epoxy and glass, re surfaced, and then painted. Short of that you may be very disappointed in a year or so when you find more blisters surrounding the ones that were fixed.


PS. This is not just for each blister, you need to do this for the entire surface below the waterline.
 
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haulnazz15

Captain
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Mar 9, 2009
Messages
3,720
Re: Sandblasting hull

Having sandblasted other items (non-marine), I'd shy away from sandblasting a surface like a fiberglass boat hull. Like ondavr mentioned, it's very difficult to remove an even layer, especially on something like gel coat. I'm sure they'd use a soft media like pecan hull or similar, but I don't see this being a long-lasting solution to exposing all of the blisters.
 

tpenfield

Moderator
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Jul 18, 2011
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Re: Sandblasting hull

I cast my vote for the surveyor's method. Those other guys must sell sand blasting equipment or something.
 

V153

Lieutenant Commander
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Apr 16, 2011
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1,764
Re: Sandblasting hull

How big a boat we talkin?
 

Volphin

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Jun 5, 2011
Messages
1,405
Re: Sandblasting hull

Uh, er, well....is your avatar a real place?

Yes, do tell. A nice place to visit I'll bet. ;)

Sea Ray had a video series back in the day that talked about blister repair. It seems to me, it was a localized solution, not a whole hull deal. I'll see if I can find a copy in my archives.
 

erie_guy

Petty Officer 1st Class
Joined
Jan 16, 2007
Messages
269
Re: Sandblasting hull

Hi eastont,
My experience with blisters was on my 32' Chris Craft. I purchased when it was two years old, having been used only in Lake Minitaka and stored on a boat lift. It had no bottom paint whatsoever and no blistering visible when surveyed. After one year stored in the water, I had a serious case of blisters - about 20 on the port side and more than 100 on the starboard side, mostly on the spray rail bottom surface. A dock friend had a Welcraft that also develpoed blisters and advised that he had the gelcoat striped off and a new surface reapplied, a very expensive repair.

To make a long story shorter, I blocked the hull up the next fall and proceeded to repair the bottom over the winter and spring. It involved removing the gel coat from and around each blister with a dremmal tool, washing each blister with fresh water, and allowing each blister to air dry for at least two weeks before proceeding. I then touched up each blister area with CPES from the "Rot Doctor" using a small artists paint brush. This thin epoxy wicks quickly into the laminate surface and I reapplied it until the blistered area would accept no more CPES. I then allowed the blisters to cure for almost a month (it was cold that winter) before filling each blister with Rot Dr's Laminating/layup epoxy that was thickened with micro spheres.

When spring arrived I lightly sanded the entire bottom with 80 grit and a random orbital sander. Next two layers of Interlux 2000 epoxy sealer was applied and when that was cured two layers of Interlux Micron anti-fouling paint were applied. First layer was shark white and the top layer was Green. Over the past 8 seasons I have not detected any re-occurrence of blistering and only have touched up the green paint when the white tattle-tail layer begins to show. This ablative anti-fouling paint is expensive, but I have only use one gallon of the green paint in the last four years.

I would not recommend either sand blasting the bottom or stripping off the gelcoat. Way to much effort and costs. If you only have a few blisters, you should be able to get the bottom fixed in a few months - just hope for a warm winter !

erie_guy
Port Clinton, OH
 

ondarvr

Supreme Mariner
Joined
Apr 6, 2005
Messages
11,527
Re: Sandblasting hull

Hi eastont,
My experience with blisters was on my 32' Chris Craft. I purchased when it was two years old, having been used only in Lake Minitaka and stored on a boat lift. It had no bottom paint whatsoever and no blistering visible when surveyed. After one year stored in the water, I had a serious case of blisters - about 20 on the port side and more than 100 on the starboard side, mostly on the spray rail bottom surface. A dock friend had a Welcraft that also develpoed blisters and advised that he had the gelcoat striped off and a new surface reapplied, a very expensive repair.

To make a long story shorter, I blocked the hull up the next fall and proceeded to repair the bottom over the winter and spring. It involved removing the gel coat from and around each blister with a dremmal tool, washing each blister with fresh water, and allowing each blister to air dry for at least two weeks before proceeding. I then touched up each blister area with CPES from the "Rot Doctor" using a small artists paint brush. This thin epoxy wicks quickly into the laminate surface and I reapplied it until the blistered area would accept no more CPES. I then allowed the blisters to cure for almost a month (it was cold that winter) before filling each blister with Rot Dr's Laminating/layup epoxy that was thickened with micro spheres.

When spring arrived I lightly sanded the entire bottom with 80 grit and a random orbital sander. Next two layers of Interlux 2000 epoxy sealer was applied and when that was cured two layers of Interlux Micron anti-fouling paint were applied. First layer was shark white and the top layer was Green. Over the past 8 seasons I have not detected any re-occurrence of blistering and only have touched up the green paint when the white tattle-tail layer begins to show. This ablative anti-fouling paint is expensive, but I have only use one gallon of the green paint in the last four years.

I would not recommend either sand blasting the bottom or stripping off the gelcoat. Way to much effort and costs. If you only have a few blisters, you should be able to get the bottom fixed in a few months - just hope for a warm winter !

erie_guy
Port Clinton, OH

While it may have worked for you so far, this is a rather unreliable method of repair, and was typical of early attempts made at fixing the problem, many law suits were created by repairs shops doing just this. There were times when it worked, but more frequently it failed, sometimes as soon as the next season. Blister repair is understood much better now and there are methods followed by reputable shops that are proven to provide long lasting results. I will not recommend a method that has high failure rate.
 

moosehead

Chief Petty Officer
Joined
May 29, 2012
Messages
437
Re: Sandblasting hull

^ondarvr, what is the general cost range for the Full Monty gelcoat peeler/removal and reinstall that you describe in post 2?
 

Home Cookin'

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Messages
9,715
Re: Sandblasting hull

It almost sounds like the cure is worse than the disease, especially on an old hull. I mean, if you have a dozen blisters, how long can you run before you have catastrophic hull failure?

Not arguing, just asking since I don't know about blisters--is it really cosmetic and not structural?

Wouldn't it be more economical to run it for a few years while keepnig an eye out for a replacement?

Just because you can fix something doesn't always mean you should.
 

ondarvr

Supreme Mariner
Joined
Apr 6, 2005
Messages
11,527
Re: Sandblasting hull

It almost sounds like the cure is worse than the disease, especially on an old hull. I mean, if you have a dozen blisters, how long can you run before you have catastrophic hull failure?

Not arguing, just asking since I don't know about blisters--is it really cosmetic and not structural?

Wouldn't it be more economical to run it for a few years while keepnig an eye out for a replacement?

Just because you can fix something doesn't always mean you should.

Very good questions, and are the ones most people should ask before doing anything about the blisters.


For the most part they are cosmetic (and I don't think the fish care), it would take a long time and a severe case to cause structural issues, not that it couldn't though.

There are times when blisters can be localized and not on the entire hull, this can be from mistakes during lamination or a few other things. So jumping in at the first sign of a few blisters and doing the whole hull "might" be overkill.

People think that fixing the blisters that are currently visible and then using a barrier coat on the hull will solve the problem, what they don't realize is these were just the first of the blisters to show up, there are many more in the larval stage waiting to hatch out of the laminate, it just takes a little more time. These non visible blister sites may continue to develop over an unknown time frame and then emerge to haunt the owner all over again, could be a year, maybe ten, or possibly never. This is why the only sure method is to remove enough of the laminate so the entire affected layer is removed.

I probably wouldn’t do the repairs on a hull I owned unless it was really bad, but at that point I would most likely get rid of it if it bothered me.
 
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erie_guy

Petty Officer 1st Class
Joined
Jan 16, 2007
Messages
269
Re: Sandblasting hull

Admiral,

Worked for me perfectly. And it has lasted since 1999 (14 seasons) without another blister. The key step is the use of the CPES which is a thin epoxy to fill and seal the fiberglass laminate within an inch or so of each blister. I suspect the failures encountered were shops that just filled the blister hole left by the ground out fiberglass with epoxy or polyester filler (for an even faster set). This is doomed for failure. Most blister related failures are local events that do not require peeling the hull. Fix the blister and then seal (barrier coat) the hull from additional moisture intrusion (osmosis) with the Interlux 2000. Problem solved !!

I was told by my dock mate that the peel job for his Wellcraft cost $2500. And that was 14 years ago. Current labor cost would inflate such repairs to $3800. Since I did the work on my boat myself, labor cost was free and materials (epoxy and paint) were approximately $900.

erie_guy
Port Clinton, OH

erie_guy
Port Clinton, OH
 

ondarvr

Supreme Mariner
Joined
Apr 6, 2005
Messages
11,527
Re: Sandblasting hull

You seem to think I said your repair didn't, or wouldn't hold up, not so, I said it was less likely to. It?s good to see they haven?t returned.

Blisters are sort of like cancer, we know a good deal about it and sort of understand many of the causes, or at least what helps it to develop, but the exact path it takes in each case is far trickier to predict. Some people's cancer goes into remission on its own, others get all the latest treatments and die rapidly. ( I was diagnosed with malignant Melanoma in 1985 and with very little treatment have had no problems since then). So because yours haven?t returned it doesn?t mean it?s the most reliable method to use.

CPES is sort of an old school product, a highly thinned epoxy, thinning epoxy greatly reduces its physical properties, and this includes water resistance. While it didn?t hurt, it?s probably not the best product to use, a standard viscosity epoxy would probably do a better job. You also had a couple coats of Interlux epoxy sealer, which is a good product.

A boat yard or repair shop can?t afford the possibility of a failure when doing a blister repair for a paying customer, so methods have been developed that help ensure a good outcome and a happy customer, which is the method I described.
 
Last edited:
Joined
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2,598
Re: Sandblasting hull

CPES is sort of an old school product, a highly thinned epoxy, thinning epoxy greatly reduces its physical properties, and this includes water resistance. While it didn’t hurt, it’s probably not the best product to use, a standard viscosity epoxy would probably do a better job......

That's a very good point. Also, you can "thin" a good quality epoxy such as West Systems with the heat from a hair dryer and it will flow and penetrate extremely well, and it won't lose a bit of it's physical properties.
 
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