Updated October 26, 2026
How surveys describe it
Wording varies by surveyor. Illustrative examples (not quoted from any real survey):
- “Scattered small blisters were noted on the underwater hull.”
- “Osmotic blistering present below the waterline.”
What it is
Blisters form when water slowly migrates into the hull laminate and reacts inside it. They range from a scattering of small cosmetic bumps to widespread blistering that needs the gelcoat peeled and the hull dried and re-coated.
How serious it is
Small, scattered blisters are often left alone or ground out and filled. A full peel-and-barrier-coat job is labor-heavy; Practical Boat Owner puts professional osmosis treatment at roughly £150 to £200 per foot of waterline in the UK.[1]
In our reports this usually lands under Watch. Your survey's details decide.
What it typically costs
| Scope | Estimated range |
|---|---|
| 30 ft boat | $3,000–$10,500 |
| 35 ft boat | $3,500–$12,500 |
| 45 ft boat | $4,500–$16,000 |
These are whole-job ranges drawn from published figures.[1]
- Per foot of boat length
- Peel, dry, re-laminate and barrier coat
- Grinding a few blisters is far cheaper
Estimates to help you frame a conversation with a yard, not quotes. Real prices depend on the boat, the yard, access and what's found once work starts. Confirm with your surveyor or a qualified yard.
What to ask your surveyor or yard
- How many blisters, how large, and how deep?
- Is it cosmetic, or is the laminate itself affected?
- Has the hull been treated before?
Have your survey already?
Upload it and get every finding sorted into fix, negotiate, watch or ignore, with the surveyor's page and words beside each one.
Get a free previewSources
- Osmosis: the professional treatment, Practical Boat Owner. Boating publication. Accessed 2026-10-26.