Seeking professional gelcoat peeling service off-site (South Coast)

Iliade said:
I cannot recall a boat sunk by osmosis. Patch repair, as and when you can be bothered, and enjoy sailing the boat. you'll probably be long dead and forgotten before the osmosis becomes actually dangerous.

Back in 1982 I was, to the best of my knowledge, the first person to plane the gelcoat off an osmosis affected hull. It cost me about 18 months of sailing time while it dried properly and was a near complete waste of time and effort and this on a lightly built 1/4 tonner. Unfortunately, I didn't patent the process...
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Your first paragraph is good advice.

If you want to fix it though drying will not take 18 months. Sandblast after peeling, then jet wash daily. A hot jet wash even better. It will be dry in weeks not months.
 
Tranona said:
The whole surface. The blasting will remove all previous coatings from thee complete area. Then fill and fair with an epoxy filler such as International Watertite then a 2 part epoxy coating such as International Gelshield. There are other similar products from other suppliers. If you are doing this yourself perhaps you need to do some research and maybe engage a surveyor to give you advice as to the best way to go about it. This is not a trivial job and will be costly in materials even if you do the labour so worth getting more knowledgeable advice than just the general advice here. Googling will lead you to plenty of advice and youtube on how others have gone about it.
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i’m afraid that’s counter to the advice the surveyor gave me, which was that to treat the osmosis, I needed to dry out the hull after repeated rinsing and that the only way to do that was to remove the gel coat.
In any case, I think the comments i’ve received are making me think it’s perhaps to job big a job for me to take on, especially as no one’s being able to recommend someone who provides peeling services (as opposed to sandblasting)
 
Elessar said:
Your first paragraph is good advice.

If you want to fix it though drying will not take 18 months. Sandblast after peeling, then jet wash daily. A hot jet wash even better. It will be dry in weeks not months.
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Weeks to a few months tallies with what the surveyor told me, though I have read about boats needing longer, and my boat yard told me that it can (rarely) happen that a boat never dries well where moisture levels are really high (as is the case with my hull). That and the risk of the osmosis having got into the fibreglass, requiring the hull to be reglassed to adequately halt the osmosis, are making me think I’ll go with Lliad's suggestion to just patch and repair as and when I can be bothered.
 
Osmosis can sound very much like a major problem, but as mentioned before no boat has ever sunk due to osmosis. On my boat, which is 45 years old, I found osmosis under a solar panel and under some TreadMaster, but none under water. When I bought Concerto I chatted with the surveyor, who was a specialist in glassfibre problems, and he recommend a decade ago to just patch any blisters and when any more appear in the future, just patch again. Eventually all the gel coat will get replaced by epoxy.

I should also mention that osmosis can also occur inside the hull, usually in the bilge, bu this is rarely mentioned as it is not so visible as on the exterior of the hull. Luckily most older hulls were structurally over built, and even most of those first built in the late 1950's and early 1960's are still around.

So, just grind out any blisters, wash repeatedly, allow to dry as much as possible, finally fill with epoxy.
 
siravingmon said:
Weeks to a few months tallies with what the surveyor told me, though I have read about boats needing longer, and my boat yard told me that it can (rarely) happen that a boat never dries well where moisture levels are really high (as is the case with my hull). That and the risk of the osmosis having got into the fibreglass, requiring the hull to be reglassed to adequately halt the osmosis, are making me think I’ll go with Lliad's suggestion to just patch and repair as and when I can be bothered.
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Let’s clarify a few things. Osmosis is the process of the water passing through a semi permeable layer (the Gelcoat). The water reacts with imperfectly mixed bits of the GRP and becomes a heavier liquid. This is why it can’t go back out through the gelcoat and why leaving boats out to dry is complete nonsense (unless they are made of wood). Yet this is still folklore.
When you dry the boat after peeling you are removing this heavier substance. Which is why water dries the boat.
So the “osmosis” in your terminology will have got into the fibreglass guaranteed. The pressure of the new heavier liquid creates the bubbles. The bits where it hasn’t yet bubbled will be just as bad. (Unless rarely just a section of the hull was poorly mixed for some reason)
For it to be un dryable the layup would need to be so poor that osmosis is the least of your worries. So it will be mendable.

However the advice to just patch and sail the boat seems the best to me. The only reason to do a full repair is for longevity and to retain value. Given the value of your boat spend the money on other things that will allow you to sail and enjoy the boat.
 
Below seems a reasonable explanation of osmosis.

A GRP boat hull is a usually a mixture of polyester resin reinforced with glass fibres, created in layers which forms a laminate. This laminate will have small voids, air pockets and microcracks within the resin and at the interface between the resin and the glass fibres. Water diffuses into and passes through the gel coat and the laminate as water molecules, not a liquid. Water may pass slowly through a GRP hull in this way or the water molecules can collect and condense within these voids. Within the voids/laminate are various water soluble components. These are solvents and unreacted constituents from the manufacturing process.

The water within the voids dissolves and reacts with these components. (Hydrolysis). The ongoing (Hydrolysis) will continue within the voids enlarging the cavities and forming a solution. The solution is water absorbing (“hydroscopic”) and once the solution is released in the voids it accelerates the rate of water absorption into the laminate. This process will not be reversed by taking the boat out of the water. As this continues the voids are increased in size and the pressure within increases. At some point the pressure may become too high for the surrounding material to support and a blister is formed. As this process continues, moisture continues to be absorbed, the laminate break down accelerates and more blisters are formed. In time some larger blisters may develop within the laminate as well as those more commonly occurring between the gel coat and laminate.

Eventually at this stage, treatment will be required as the structural integrity of the hull can be effected.

The water and the contaminants in the laminate have to be removed and whilst drying will remove the water it leaves many of the contaminants behind so for this reason steam cleaning and washing the hull surface is important but not sufficient. Depending on how big and how many blisters you have, the decision on how much work is down to you. A few isolated blisters can be carefully cut off with a chisel, washed out and filled with epoxy resin. Even large blisters can be treated this way.

Peeling the gel coat is common but extreme and on its own often adds to problems. Blisters will return, even after peeling, if there are still voids in the laminates and uncured gel coat, more blisters will occur. So if you are the owner and don’t intend to sell, my personal view is deal with them individually as they occur. If you are planning to sell, yes the fact is, boats with untreated osmosis are harder to sell, so you will need to get a professional, warranted job done.

The gel coat is a very effective water barrier and does not allow the passage of glycols so it has to be removed usually by the use of a “Gel Peeler”. This removes a controlled thickness of gel coat/laminate leaving an even surface.

To promote drying and to abrade the surface left by the “Gel Peeler” the peeled surface should be “grit blasted” after peeling, for maximum effect this work should be done immediately after the end of the season. Thereafter the hull should be steam cleaned and washed regularly for a period of time to ensure that the solutions are washed out. At this stage, I would recommend HOTVAC treatment. This cures the uncured resin and reduces he chance of re-occurrence. When the surface is found to be neutral, the drying process can commence. Initially this can be air dried but eventually the hull will need to be heated to reduce moisture content to a very low level. Once the hull is dry a new coating can be applied.
 
Rappey said:
Below seems a reasonable explanation of osmosis.

A GRP boat hull is a usually a mixture of polyester resin reinforced with glass fibres, created in layers which forms a laminate. This laminate will have small voids, air pockets and microcracks within the resin and at the interface between the resin and the glass fibres. Water diffuses into and passes through the gel coat and the laminate as water molecules, not a liquid. Water may pass slowly through a GRP hull in this way or the water molecules can collect and condense within these voids. Within the voids/laminate are various water soluble components. These are solvents and unreacted constituents from the manufacturing process.

The water within the voids dissolves and reacts with these components. (Hydrolysis). The ongoing (Hydrolysis) will continue within the voids enlarging the cavities and forming a solution. The solution is water absorbing (“hydroscopic”) and once the solution is released in the voids it accelerates the rate of water absorption into the laminate. This process will not be reversed by taking the boat out of the water. As this continues the voids are increased in size and the pressure within increases. At some point the pressure may become too high for the surrounding material to support and a blister is formed. As this process continues, moisture continues to be absorbed, the laminate break down accelerates and more blisters are formed. In time some larger blisters may develop within the laminate as well as those more commonly occurring between the gel coat and laminate.

Eventually at this stage, treatment will be required as the structural integrity of the hull can be effected.

The water and the contaminants in the laminate have to be removed and whilst drying will remove the water it leaves many of the contaminants behind so for this reason steam cleaning and washing the hull surface is important but not sufficient. Depending on how big and how many blisters you have, the decision on how much work is down to you. A few isolated blisters can be carefully cut off with a chisel, washed out and filled with epoxy resin. Even large blisters can be treated this way.

Peeling the gel coat is common but extreme and on its own often adds to problems. Blisters will return, even after peeling, if there are still voids in the laminates and uncured gel coat, more blisters will occur. So if you are the owner and don’t intend to sell, my personal view is deal with them individually as they occur. If you are planning to sell, yes the fact is, boats with untreated osmosis are harder to sell, so you will need to get a professional, warranted job done.

The gel coat is a very effective water barrier and does not allow the passage of glycols so it has to be removed usually by the use of a “Gel Peeler”. This removes a controlled thickness of gel coat/laminate leaving an even surface.

To promote drying and to abrade the surface left by the “Gel Peeler” the peeled surface should be “grit blasted” after peeling, for maximum effect this work should be done immediately after the end of the season. Thereafter the hull should be steam cleaned and washed regularly for a period of time to ensure that the solutions are washed out. At this stage, I would recommend HOTVAC treatment. This cures the uncured resin and reduces he chance of re-occurrence. When the surface is found to be neutral, the drying process can commence. Initially this can be air dried but eventually the hull will need to be heated to reduce moisture content to a very low level. Once the hull is dry a new coating can be applied.
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Thanks, that matches my previous learning about the subject. As I was gifted the boat I’ll focus on just sanding back the anti-foul and gel coat where the worst blisters are and grinding out the blisters, followed by repeated washing with hot steam, drying and epoxying.
 
siravingmon said:
Thanks for. that, I’ll have to ook into the best techniques for sanding antifoul and gelcoat back, as well as the best tool for grinding out blisters
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Antifoul is the worst for dry sanding. Scraping is possibly the best way. Used to be able to buy a scraper that allowed a vacuum cleaner to be attached.
When grinding gel coat blisters I used a dremel, holding with one hand and the other hand had the vacuum cleaner. Luckily the blisters were small !
 
I second Rappey. Brushless die grinder with carbide burrs seems to make short work of small blisters - cuts faster and neater than a small grinding bit would.
 
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