Curing the pox

[clyst]

Hi all , when I last had the boat craned out a few years ago I noticed a few small blisters so this year I'm coming out for the winter with view to tackling the pox . Since storage will be outside I propose to employ the local blaster to get rid of the AF and hopefully remove the tops of the blisters without to much damage to the remaining gelcoat. Now do I pressure wash the poxy bits after blasting then skirt the from the waterline to ground with polythene or leave open to the elements ? Anyone successfully done and cured the pox outdoors in the past ?
Cheers .qq

 

[Deleted member 36384]

The real answer is it depends. A sailing associate had his boat on the hard at Ardfern, under cover, and the spots did not dry out over a couple of years, even using heat lamps. The only sure fire way is to use a heated vacuum mat over the area. As you suggest wash copiously with fresh water, over and over again. The fresh water will not enter the opened up blisters into the laminate as you need time for that to happen i.e. the exposed surface is not a sponge. You are really just washing away any product that comes to surface. You may find that after washing and cleaning, that is it, they will dry out easily over the winter and you can repair with epoxy. If using a moisture meter you need to make sure that there is no water behind the laminate e.g. water tanks or trapped water in stringers, it will show up on the meter. I tested this on my own boat in the cockpit, the meter was placed against the cave locker and showed no moisture, I then pressed a water bottle against the inside surface of the cave locker and repeated the test, it now indicated high moisture levels.

If the blisters are small you may get away with it and they will dry out over the winter, wash frequently. You may not get away with it if there is bigger problem in the laminate.

That's my understanding as an amateur with an old boat that looked into this matter.

 

[yoda]

Such a hard question to answer because of the variables. There is a strong argument that peeling the entire gelcoat under the waterline is essential to enable all the substrate to be exposed and then washed and dried. On the other hand blasting will minimise the work required down to the localised areas that are currently affected but may not get to others where the early stages have not yet weakened the gelcoat. You also have to consider resale and what a potential buyer may want.

With all that said I had mine blasted and then spent 8 months hot and cold pressure washing the hull before going through the process of filling, fairing and coating. The key is that you have to remove the contamination and steam cleaning is the best way to do that. After that drying is required and exposure to the wind is probably the next best thing to hot vac which speeds up the process. Mine was all done outside with the restoration process starting in about May and completing in late June. Access to a moisture meter is also important so you can see how well the hull is drying out. My the way the filling and fairing is hard work!!!!

yoda

 

[<152587>]

PBO article with Tony Statton-Bevan February 2016 available on the web.

 

[neilf39]

Can't say I cured it but I got my hull soda blasted one October and filled the popped blisters with epoxy in late March. I think most of my blisters were small and dry anyway. Put a coat of primer and 4 coats of gelshield on afterwards. So far after a couple of years I haven't seen any blisters re-appear. Not sure if it will last and most people said it was a waste of time but thought I would try it given that a the proper treatment would cost £7k on a boat worth £15k.

 

[clyst]

Thanks for taking your time to comment chaps since I don't want to go down the road of all the hassle if I have all the gel coat removed ....especially in the open. I will take a chance and do It as gentle as I can and hope if I PW through the winter I wash all the nasties out ,although as Yoda says there may be others hiding ready to show theirselves in the future .
Cheers .

 

[Howardnp]

I've just about completed this on my 10m boat and it took a lot longer than I imagined. I did it myself as the cost of a full osmosis treatment couldn't be justified from what I paid for the boat in the first place (as mentioned above).
A few comments :

Drying it in the open over winter? Difficult. I put a plastic screen around (taped sheets to the hull) and not forgetting to put sheets over the floor - otherwise you get condensation on the hull from damp/wet floor.
I had a small fan underneath to circulate air and a dehumidifier inside the boat as well.
Only taking off the blisters may miss problems you can't see... if there are a lot of blisters then gel peel it all (that was my start point).
Once gel peeled it's a case of sanding it and fairing it...you'll have time as it isn't a five minute job drying it...especially in winter.
As above, a moisture meter is essential...worst areas started at 17% and most areas when I started sealing it had dried to 3%
Check the blisters and substrate, thankfully mine were many but small - we think someone may have sandblasted antifoul off in the past and the sand had perforated the gel coat. I didn't have and substrate issues and few weeped.
Yes wash it off
Then used Gelshield 200 and after the first coat I used Watertite epoxy to fill pinholes and hollows
Then 5 coats alternating grey green

The gel peeling was done by a travelling gel peeler, Josh, he came down from Glasgow (to Worcester) with his assistant and all the gear, one overnight stay, mileage and it cost about £1k - excellent value I thought.

Good luck

PM me if you want more info or a chat