Osmosis Blisters

[Mattoc]

When hauled out, my 1980's Westerly had 15 - 20 darker circular patches about a 50p piece in size on the port side, both the yard pressure washer man and I presumed they were osmosis blisters.

The boat was put in a cradle, and a couple of hours later when I went to have a closer look, the darker patches had all disappeared and with them all visual signs of osmosis.

The boat has nor been dry for 10 weeks, and is likely to remain on the hard for at least another 8.

When she goes back in, it will be 2 years until she is next ack out, and then hopefully just for a quick antifoul.

As she is now as dry as she is ever likely to be, I am wondering if it would be a good idea to blast the hull to remove the antifoul and apply GelShield protection.

I'm thinking that would protect the rest of the hull and reduce the chance of visible blisters in the future.

Advice much appreciated.

 

[Concerto]

It certainly does not sound like osmosis, more likely to be a layer of antifouling bubbling as it has now deflated as it has dried. If you can find where one of the bubbles was, it would be worth seeing if there is a bonding problem between antifouling layers. If there is a problem then full removal would be adviseable.

My Fulmar remains in the water for 2 years and has no real problems. 8 years ago I removed all the old antifouling and applied Gel Shield. My hull sufferes from micro bubbles due to poor brushing out of the gel coat, so I only applied 3 coats on the advice of the surveyor.

 

[Refueler]

Personally - I would advise against wasting money on Gelshield if you have not 'popped' washed out and dried those blisters.

Applying Gelshield as you suggest may just lock those blisters in.... IF blisters

If the 'dark patches' disappeared quite quickly - then I would think they may be areas subject to 'wicking' .... basically tiny access into the strata allowing water to wick in ... the strata could be failed adhesion of any 'paint / AF' or gelcoat.
Pity that you did not open up them when they were obvious ... then you would have had the answer.

My boat stayed in for near 10yrs with small areas of 'concern' ..... when lifted out 20-21 winter - I took drill with grinding bit to open them up .. pressure washed ... dried and then filled with epoxy ..... when I lifted this winter ... allbut one were still as filled ... so I just re-filled the one.

 

[Bobc]

Doesn't sound like osmosis to me, and if it is, epoxying the Hull will only trap the moisture in.

 

[Wansworth]

Just as an aside back in the 1980sI worked in Place where boats were molded.I had no training and really no idea what I was doing and certainly had no supervision.Bucket fulls of resin were mixed up with gay abandon if that’s possible.The bosses had little orno idea relying on a foreman who had been in at the beginning of grp lamination and seemed to be a bit slap dash.In reference to osmosis it’s probabably not so much the material as the workmanship

 

[CAPTAIN FANTASTIC]

Even if it is blisters due to osmosis, it does not matter. Delamination is a much more serious issue, but it is not very common.

 

[Mattoc]

Thanks for all the advice, I stick with plan A, just antifoul this time round, and investigate further at next lift out, but a bit more promptly next time.