Treating osmosis blisters

[killick]

My 1988 Sadler 26 has,some years ago,been treated for osmosis by the previous owner. It would appear as if he had only covered the hull in a thick layer of Nomosis and did nothing about the actual problem. I now have thousands of small,less than 10 mm,blisters which I am opening,draining,washing with fresh water and allowing to dry out before filling it with an epoxy filler and covering it with epoxy sealer,primer and antifouling. I find that the blisters that I open with a chisel weeps while those that i grind open with a small grindstone attached to a drill does not. Could it be that the heat generated by the grindstone seals the hole and prevent proper drainage? Any advice will be greatly appreciated.

 

[SHUG]

If you have "thousands of blisters" it looks like a case for an eventual gel coat peel.
I don't however think that it is particularly urgent. It would be a mistake to put on any sealing layer before you decide to do the full treatment.

 

[single]

Just leave it.I had mine done and its all come back after 6 years.Waste of time and money.

 

[pcatterall]

Wouldn't spend loads of time on the filling and faring operation as it will only be temporary whether you do it well or not

 

[killick]

Wouldn't spend loads of time on the filling and faring operation as it will only be temporary whether you do it well or not

The value of the boat does not make stripping of gel coat economically worthwhile.The blisters seem to be very shallow and I would like to do the job as well as possible under the circumstances.In our hot African climate hulls dry out fast and I hope that with so many openings in the gel coat there should be a significant amount of drying out over time.Thank you for your comments.

 

[oldsaltoz]

The value of the boat does not make stripping of gel coat economically worthwhile.The blisters seem to be very shallow and I would like to do the job as well as possible under the circumstances.In our hot African climate hulls dry out fast and I hope that with so many openings in the gel coat there should be a significant amount of drying out over time.Thank you for your comments.

Hi Killick,

You need to take moisture readings to get the best results, Take readings above and below the water line, then the deck area. The difference between deck and above waterline should be close, but expect below the water line to be higher. The difference will give a good indication of when the hull is dry enough to treat.

Treating a wet hull will only make matters worse as it traps the moisture in the hull and accelerates the problem.

Chipping the spots will result in a flow, grinding them results in particles blocking the passages, high pressure washing removes this, and regardless of what method you use, the high pressure washing every few days is a requirement, not a nice to have. You need to water in to dilute the residue.

Try to line up the boat so that you get the sun on both sides in a course of the day if possible, every little bit helps.

When filling use Micro-spheres they are glass bubbles, so more waterproof than Micro-Balloons, but are still easy to sand back. Using solvent free Epoxy resin also helps.

Good luck and fair winds.