Gel Coat Advice

[Kirt86]

I recently had a survey done on my boat (1984 - been in the water for at least the last 8 years) which revealed some issues with the underwater gel coat.

The surveyor recommended a period out of the water, removal of gel coat and full reapplication, which I am considering, but does anyone have any experience of similar adhesion problems or alternative solutions (that wouldn’t mean the boat being out of the water for the majority of next year)?

Extract from survey report below:

 

[Concerto]

Welcome to your first post. What took you so long?

I presume you are the owner, not looking to purchase the boat.

I am not an expert in glassfibre problems but do know quite a lot. The intial photograph looked like some of the bubbles could have been air bubbles trapped within the gel coat as they looked to be 2 to 3 mm in diameter. Anything larger that this is most likely to be osmosis. When the blister in the second photograph was broken open, did it have a vinegar smell? If so, then it is most likely to be osmosis. If it was only a single place, it might have been an impact damage but this looks unlikely.

It would be helpful to say which class of boat you have. This may help if there are other know problems with this class or manufacturer.

My intial advice would be to strip an area of antifouling about 600 to 800 mm square and closely look at all the other bubbled areas. This should show if the problem is replicated on a smaller scale. Depending on the result, you may need a full gel coat strip or localised blistered areas. If you follow the latter policy, you may require to fill more blisters in the future. This option would be the cheapest and possible to do yourself, whereas the complete gel coat strip is a wallet busting cost.

 

[Gsailor]

Removal of entire gel coat would be extreme and costly. Then of course you have to make good.

The saying goes “ no boat ever sunk owing to osmosis” - I do not know whether true or not.

There are machines that place pads against the hull and heat AND extract moisture - I have no links - it is 20 years old knowledge I am talking about.

I wish you luck and more importantly, good sailing - boat maintenance can be fun and I used to prefer it to car maintenance, but some people prefer to sail and others actually enjoy maintenance and boat building more than sailing.

 

[Gsailor]

PS I do not know your boat or it’s value but my first cruiser had greater blisters than your phots show and I ground out, dried, and filled and sailed it for years and sold for a large profit.

 

[Tranona]

Welcome to the forum

Endorse what Concerto says. The boat appears to have osmosis, which is common in boats of that age. What you do about it depends on the extent of the blistering and the value of the boat. In the past complete strip dry out and epoxy was a common solution. But this was when relative values of boats were higher or more directly the cost of treatment was relatively low in relation to the value of the boat. nowadays that is no longer true. costs of such work have risen and values of boats have fallen. in addition experience has shown that such treatment is not the panacea that one might imagine and failure is not unknown.

So now it is more common to accept that the condition exists - it was potentially there from the day the hull was moulded - but that generally it does not result in structural weakness and localised repair on an ongoing basis is a viable alternative. While your surveyor has identified holes on the entire surface he has only cleared small areas and probed further, so the next stage is to let the hull dry out then scrape as much antifoul off as you can to see if the blisters are as extensive and deep as the example shown in the report.

 

[Gsailor]

It would be interesting to know the boat or perceived value. Or the value of similar vessels with zero defects.

Having expanded the photos and read the comments I would employ a different surveyor to compare - his comments seem butt covering and scare mongering - I would sail your boat as is wherever you wanted (depending upon what boat it is and what equipment is on board).

But perhaps there is more I am not seeing. He seems to covering his butt.

I can see not a lot to warrant an entire shave.

Perhaps the entire hull is covered in gaping holes? But that’s not been shown.

More info needed really.

 

[Kirt86]

Thanks for the replies.

I’m fairly certain it’s not osmosis, the majority of the holes are ~2mm and there is not really any blistering, it’s only when you dig away at the holes that the gel coat seems to just fall away from the hull like it isn’t adhered properly. The section in the photograph is the worst affected area.

The boat is my boat (Sadler 32). The cost of a full strip would almost certainly amount to at least half the boat’s value, but I’m happy with everything else and not looking to sell anytime soon so sounds like a course of gradual repairs is a better option. It’s been in the water (in the Med) for many years and only comes out once a year for a couple of days to do antifouling/minor repairs so doesn’t really help.

 

[Stemar]

I'm no engineer, but the boat's nearly 40 years old. In spite of the "inadequate adheration" (is that a word?), the gelcoat hasn't fallen off, so it's unlikely to in the next 40 years.

We know nothing about the boat. If she's a sub-30ft cruiser, I'd be inclined to show this to the seller with a great sucking of teeth and offer to take her off his hands for half what he's asking. Then I'd go sailing, filling the holes with epoxy filler as and when. If she's a classic ocean greyhound, then a gelcoat peel is probably worth doing, but you'll want to be sitting down when they tell you the price

 

[fisherman]

The holes don't look like osmosis, there would be blisters as well as you say. Sounding didn't show widespread lack of adhesion? Where the gel is damaged the usual is to grind back, including the first few mm of substrate if necessary, until sound GRP is found, then apply mat/resin, (polyester or epoxy, the argument about which rages on), and remake the gel coat.
Peeling and recoating, expensive, my mate did it himself. Not the peeling, he got people in for that, but he rolled on multiple coats, alternating colours. Ambient temp was the main issue.

 

[Tranona]

Thanks for the replies.

I’m fairly certain it’s not osmosis, the majority of the holes are ~2mm and there is not really any blistering, it’s only when you dig away at the holes that the gel coat seems to just fall away from the hull like it isn’t adhered properly. The section in the photograph is the worst affected area.

The boat is my boat (Sadler 32). The cost of a full strip would almost certainly amount to at least half the boat’s value, but I’m happy with everything else and not looking to sell anytime soon so sounds like a course of gradual repairs is a better option. It’s been in the water (in the Med) for many years and only comes out once a year for a couple of days to do antifouling/minor repairs so doesn’t really help.

It might be worth having the hull blasted to remove all the antifouling which will also remove all the loose gel coat, but not enough to remove sound gel coat. You will then be in a better position to eliminate osmosis if the small blisters do not open up and weep fluid. if all is sound then filling and fairing where the gel coat is missing followed by complete epoxy coating should work.

 

[Bodach na mara]

Like Tranona says in post #10 I don't think that the problem is osmosis. If it were not a Sadler I would suspect poor lamination technique, possibly allowing too long after applying the gel coat before starting on application of the main reinforcement layers. If the defect is localized it may be down to a poor repair of damage to the hull but I would have expected a surveyor to have found other evidence to comment on.

As others have said, limited gel coat removal followed by drying out and reinstatement of the outer surface may sort the problem. That you mentioned that the hull had been in the water for 8 years seems to confirm my own view that boats benefit from being removed from the water to dry out annually.

 

[Concerto]

Thanks for the replies.

I’m fairly certain it’s not osmosis, the majority of the holes are ~2mm and there is not really any blistering, it’s only when you dig away at the holes that the gel coat seems to just fall away from the hull like it isn’t adhered properly. The section in the photograph is the worst affected area.

The boat is my boat (Sadler 32). The cost of a full strip would almost certainly amount to at least half the boat’s value, but I’m happy with everything else and not looking to sell anytime soon so sounds like a course of gradual repairs is a better option. It’s been in the water (in the Med) for many years and only comes out once a year for a couple of days to do antifouling/minor repairs so doesn’t really help.

It could be due to poor lamination and years of use has taken its toll on the bond between the gel coat and glassfibre layers.

Years ago I remember seeing a 40 odd foot long boat which was about 40 years old for sale on eBay. It had just returned from a transatlantic crossing and it was sold subject to survey. A couple of months later it was back on ebay at a price half what it had been. The buyer had backed out due to the surveyor finding extensive delamination in the hull. Someone did buy it and I presume fixed the problem.

If I was going to fix any area on your hull I would dry any affected without disturbing too much of the surface. Then drill a 6mm hole at the top of the hollow sounding area but only through the loose surface. Seal the damaged surface with a plastic tape and then inject liquid epoxy into the void. Gravity will fill every crevice with epoxy. You will use far more epoxy than you expect.

I used this to fix an area on Concerto's foredeck that showed a similar problem with a plywood . I used 4 times the amount of epoxy to fix the problem as it spread further than I expected. It certainly solved the problem.