I was faced with a similar situation before purchasing my current 36 ft. boat last November. However, there was no question in my mind whether or not to hire a certified Surveyor. Hire the best surveyor you can afford, it''s money well spent for peace of mind and leverage for reducing the amount of your initial offer.
My surveyor removed portions of bottom paint
prior to moisture testing; the bottom was relatively dry, with some spot readings in the low 80''s, but soundings indicated no nonlamination or hollow areas. His findings were recorded in the written report & backed by a CD of survey photos. He said the job was worth $9k with the seller agreeing to a $7k reduction to my accepted initial offer. This was backed by a written estimate from the reputable boatyard I ultimately hired to do the work.
The blisters were very small, but still present and after bottom stripping, drilling/grinding and pressure rinsing, the hull was fully tented with poly for 2 months of drying in a radiant slab heated shop. When moisture readings were in the single digits, certified techs worked on the final filling, fairing & spray application of InterProtect 3000 epoxy
. The bottom is now fully prepared, smooth as glass and ready for bottom paint
Consider retaining the surveyor at intervals during the drying process to certify moisture readings prior to filling. This will increase the value of the boat for the next owner and confirm that the hull has acceptable levels. Any remaining osmosis fluid may eventually return as blisters.