Osmosis

[maldhorror]

I have a 35 years old trintela with a hull made of grp sandwich(fiber)
When scrubing down to the gellcoat in order to change the antifouling I found a few bubble (more or less 4 per scuare foot)
I do not know what to do
Some people say that I have to treat the whole hull
Others that with the age of the boat and the tipe of construction It is normal and I should not worry.,just pinch them, let them dry for a few days and apply new gel coat
Any suggestion?

[Franziska]

If it is very few, open them, wash with acetone and let thoroughly dry.
Fill them with Epoxy(!) filler.
Sand complete (!) underwater to bare gel coat, dedust and apply at least two coats of epoxy (!) osmosis shield like tarepoxy or similar.
Apply anti fouling.
Go sailing.

If you have few blisters and only work locally with the epoxy shield you will not get rid of the problem long-term.

New gelcoat will not help, polyester based products do not work as osmosis barriers.

[boatman61]

I kinda agree with the above..
Open the blisters then hose them really well with fresh water taking time over it to flush them well.. leave to dry a couple of days then grind each blister back to clean area about 1inch circumference around each one and till touching glass then wash hull again and dry..
Fill with epoxy filler then prep whole hull before applying coats of epoxy sealer..
Some will suggest peeling but most I have seen done need doing again in a few years..

[deltaten]

Doing a bottom job currently, so this thread is of considerable interest!
One side of the keel has considerable spider web crazing; some terminating in blisters, nearly all of them are dry.
Question being; what happens when a small wet blister gets overcoated with epoxy? It would seem that the osmotic action would stop, as no more water would be available. Would the existing solution saturate to the point of "choking" itself and cease "eating" resin?I
Should I suspect that a 5coat/10 mil layer of barrier epoxy will fill/bridge the (apparently) cosmetic spider cracks?

TIA,
Paul

[boatman61]

I think you'll find it will feed itself with moisture already trapped/absorbed in the gelcoat..
The blisters need popping and draining of the near acidic fluid created in the process else it will slowly progress to wicking as it penetrates the fibres.. then its a major project..
Better to do it right first time and nip it in the bud if your keeping the boat for a long time..
If your moving it on end of season do the bodge job and let the next owner have the hassle.