Osmotic Blisters

[Thisisit]

I discovered a quarter sized blister on the bottom of my 3807 about 5 years ago. In the fall, once laid up, I opened them up, let them drain and ground them out. I let the cold winter dry them out and in the spring, I sanded, cleaned them with TSP and filled with West System. A primer coat and bottom paint left it like new.

[Thisisit]

I should have added that after closer inspection, once finding the first blister, I located 32 others. Most were pea sized.