I have unfortunately some experience with Osmosis, in fact two of my previous boats had osmosis.

First time I had it treated immediately I saw it. They “gently” sandblasted the bottom and after one could see numerous “craters” about 20 mm in diameter but the depth was not very deep at all, my and the yards conclusion after that was that I could have had the boat for many years without any problems at all. There was no weakening of the structure at all. The boat was treated and I had it for another 6-7 years without seeing any new blisters.

                           I bought another boat (well known type) from 1973 I think it was 2004, had it inspected for osmosis and it was declared free of osmosis, but already after the first year I saw some signs of osmosis, small like (volcanic) craters with some yellow dust on top of. At least in Sweden that I clear sign of osmosis, but you need to get close to see it. After my first experience I did not worry too much, but each year it get worse and worse and after three years you could see immediately after end season that this boat got blisters and a lot. I had a well-known professional yard looking at it and they said this was one of the worst cases they have seen. They sand blasted and washed with a lot of water the water wash is very important to take away all chemical residuals from the processes that cause the osmosis. Then the hull needs to dry out not from the wash but from all the water that had been adsorbed of the years. That can go fast or take very long time. In my case it toke ca 14 month, but usually not more than 3-6 month (Sweden not very hot and rather high humidity in the fall), my budget did not allow heated storage inside. Any conclusion from that? Well usually no problem with blisters, but if you treat it wash and dry very carefully before applying new coats of epoxy.

S/Y Kerpa