Pimples under paint

[Greenheart]

Probably it wasn't good quality paint, and I doubt it's been on the boat more than a year. It was always part of my plan to get rid of it, but it looks to me like it's now beginning to depart without encouragement...

View attachment 38990

...lots of pimples are rising off the surface. They've definitely come up in the last couple of months. I don't care about this paint...but I won't want the decent paint which I eventually replace it with, to fail in the same way.

Any ideas what's causing it? Thanks.

 

[Pasarell]

Is that the side deck of a dinghy? If so, do you keep a cover on it? A plastic cover that sits on the deck will trap moisture against the surface and a cheap paint, especially single pack or a thinnish coat will allow water to penetrate and blister underneath the film. If it's a different area may have to think again but still quite likely to be water getting under the dry film in some way

 

[boguing]

Agree with Pasarell. Emulsion or poster paint lasts forever if it doesn't get UV'd or damp! Top quality two pack won't last forever when exposed to the elements.

As long as you stick to the instructions for a good quality paint, it won't blister. That means proper preparation of the old surface (which will certainly mean totally removing that green stuff) and then priming and undercoating.

When finished, the better you protect from water and sun, the longer it will last.

 

[Greenheart]

Thank you gentlemen, it is mainly on the side decks. There's lately been a six-week period when I couldn't visit the boat, so I can easily believe damp will have built up then.

Actually she has a pretty good quality 'breathable' cover which I normally make an effort to keep correctly in place, and the transom drains stay open for air-flow. And I've made an effort to ensure the boat is dry whenever the cover goes on.

The rather old paint I plan to replace the green with (bought in '03 and never used) is good stuff by International - Interlux Super - I was only concerned that there might be a problem in the underlying GRP (or the thick core of wood) which needs sorting before any new paint goes on.

I sense an approaching bill for lots of sandpaper and face-masks. Is there a recommended hard-wearing undercoat which you'd advise for putting under the Interlux?

 

[TimBennet]

Even top quality two pack linear polyurethanes will blister if kept wet.

Awlgrip warns "Do not allow wet equipment (e.g. seat cushions, coils of line, sails, sail covers, coolers) to trap and hold moisture against Awlgrip Topcoats. This condition can result in blistering or delamination of the Awlgrip or Awlcraft 2000 Topcoat".

We've even had topcoats blister at bows and along the waterline where a boat has undertaken an extended passage on one tack and the bow wave area and lee-side have been immersed.
When we queried the problem 20 years ago, US Paints (as was then) admitted that 'waterproofness' was not a strong feature of their marine paints and added more caveats to their care leaflets.

 

[Greenheart]

Even top quality two pack linear polyurethanes will blister if kept wet.

US Paints (as was then) admitted that 'waterproofness' was not a strong feature of their marine paints and added more caveats to their care leaflets.

That seems shocking, except it's wholly believable. Good advice about letting nothing stay damp, thanks.

I expect my weekly (or more frequent) visits to my boat during last year's slightly drier seasons are the only reason why the green paint lasted as long as it has.

 

[Iain C]

Dan

I had an old foam sandwich Fireball (a Northampton Sailboats jobbie) that did the same under the gelcoat. Keep doing what you are doing in terms of keeping the boat as dry as you can and you will probably find in the summer that they pretty much disappear.

 

[Greenheart]

Thanks Iain. I'm sure this perpetual rain isn't doing anyone's boat any good. But thinking back, I can mostly answer my own question...the bubbles under the green paint are loose and high for their diameter, and easy to 'pop', so I'm sure it's the paint rather than the gel coat which is coming up. The 'problem' is possibly making my scheduled repaint, easier!

I'd love to put up our 8-man tent around the boat, not sure what the sailing club would say, though. Maybe during sanding and painting it'd be okay.

 

[Iain C]

Dan

The GRP on your boat is likely to be very wet. Strands of CSM not fully impregnated with resin are going to "wick" the water from the atmosphere, sailing, rain etc. You may find that if the gel underneath is old, the water may permeate up anyway...you could take all the paint off, do a lovely job and have the same thing happen...

 

[doug748]

Even top quality two pack linear polyurethanes will blister if kept wet.

Awlgrip warns "Do not allow wet equipment (e.g. seat cushions, coils of line, sails, sail covers, coolers) to trap and hold moisture against Awlgrip Topcoats. This condition can result in blistering or delamination of the Awlgrip or Awlcraft 2000 Topcoat".

We've even had topcoats blister at bows and along the waterline where a boat has undertaken an extended passage on one tack and the bow wave area and lee-side have been immersed.
When we queried the problem 20 years ago, US Paints (as was then) admitted that 'waterproofness' was not a strong feature of their marine paints and added more caveats to their care leaflets.

A very interesting post.

Having an Awlgrip painted hull I have a long standing dislike of all marine paints and, for that matter, coloured hulls. I have even seen Awlgrip blistered at the waterline where a boat has been kept on a lively swinging mooring.

Are "re-gelcoated" hulls an all round better prospect? Are they better in this particular respect?

 

[Greenheart]

The GRP on your boat is likely to be very wet...you could take all the paint off, do a lovely job and have the same thing happen...

Eeek! That's not good to hear.

When I made some serious repairs last year to cracks between the 3" overhanging gunwales and the rest of the side decks, the GRP seemed dry and clean, although drilling right through the overhangs (to fit rowlock sockets) there was indeed a suspicious damp appearance to the wood core, which I doubt is fixable within a tight budget.

Maybe I'd be better off Pro-Gripping the entire side-decks...assuming contact adhesive isn't similarly subject to 'rising damp'? I'll need some non-slip on the gunwales in any case.

Either way, I bought the good paint ten years back so I won't lose much (except the awful green) by replacing the affected paintwork. It's an old boat and I'm not a perfectionist.

 

[oldsaltoz]

It dose look like an area that has been sanded and exposed the underlying glass fibres thus allowing moisture to enter.

Not the end of the world or horrendously expensive to correct. Just sand back, seal and prime.

Good luck and fair winds.