Blistering paint

[anoccasionalyachtsman]

Bought a 1980 dayboat last year which had been stored ashore for a while with a 'canvas' boom tent. Topsides not in great condition, but fine for its age. It had been dry sailed for all of its life so I'm epoxying before anti-fouling.

However... Above the waterline there are a couple of areas of blistering that have appeared over winter. The larger of them was underneath where a plastic tarpaulin was tight against it, the other in free air. The whole boat was out of direct sunlight.

Both areas are directly below points where water could have got between the gelcoat and paint - at the transom there was cracking in the filler at the hull/deck joint, and the area on the topsides is below where the chainplate emerges (chainplates are flat plates bonded to inner hull surface and come up through a cutout in the deck edge which is then filled - sealing the gap is known to be 'impossible' in the class) The paint covers this.

I've never seen this happen before. The blisters are water-filled, and I was able to lift a square foot off the transom with a wallpaper knife quite easily. the underlying surface doesn't look at all well keyed. The rest of the transom appears sound and I was able to sand back to a good wide feather edge - previous experience says that poorly applied paint won't take a feather edge - anyone disagree?

What I need if for you all to tell me that water penetration through cracks is quite common, always stays localised and that sanding back and recoating, as well as preventing further ingress will be good for decades.

My worst fear is that the paint is porous, the tarpaulin held water against it and therefore caused the topside blisters. Which means that keeping it afloat will result in maritime psoriasis and I'll be drummed out of the club that I've just joined. But you don't want to tell me that because the forum will, as usual, be completely positive and in full agreement..

 

[Paddy Layback]

Blisters!

 

[William_H]

Well I know what I would do. That is just bodge the painting by cutting out blisters sand sand back as far as you can. (have the energy for) Slap some paint on and go sailing. Next winter refurbishment will show if you are being too worried about it all. If it is a grp boat no problems. If it is wood then look for rotten wood which will be a problem. No you won't be drummed out of the club or even feel embarrassed if you keep touching up the paint. good luck olewill

 

[Pasarell]

Pretty much as William says. It's almost certainly a single pack paint and if it has had water held against the surface by the plastic that water will have penetrated through to form blisters between topcoat and primer. If it was painted coat on coat originally there will be no visible key as the bond between topcoat and primer / undercoat would have been chemical, not mechanical. Water will break that chemical bond down and allow the topcoat to lift off. I would take the blisters back a couple of cm all around their edge, abrade lightly and recoat before going sailing

 

[anoccasionalyachtsman]

Excellent. I'll carry on with plan A, and then keep my fingers crossed.

Thanks all.

ps. Paddy - I was so cross that I nearly kicked Snowy.

 

[anoccasionalyachtsman]

It gets worse. Hanging from a crane to get to the parts I couldn't raech due to the trailer.



I didn't make it completely clear in the first post, but the boat has been painted - several years ago judging by the discolouration, scrapes and re-emerged star cracking. I just don't understand why it's waited until now to happen. When I bought it it was stored in a yard where plenty of sunlight and breeze could get to it, but I've kept it in a gloomy dank spot since September, but I'm reluctant to believe that this could be the cause. Maybe made it worse, but not cause?

Could it be that the previous owner had been pricking them and they'd flattened out? Doubt it. It's an open racing boat, so it could have been sunk and recovered - would that do it? As we agreed previously, best thing now is carry on, so I've sanded these bits back to good gelcoat and will do three coats of epoxy - I've only put two on the rest and then antifouled, so can't really add more. Depressing though, because I'm fairly sure that the topsides will break out as soon as it's in the water on a mooring, and when it gets under the paint it can then travel down and under the epoxy. Further blues because I could easily have gone back through all the old paint if I'd known this would happen, but I just abraded.

So two questions really. Anyone seen anything like it, and where would you suggest for a wet blast back to laminate this winter? Have trailer, will travel.