Just purchased a used boat - all looks good except for a couple of places on the hull where there are wart like hard bubbles . Any ideas what they could be ? are they detrimental and if so - how can they be remedied?
I had something virtually identical to this on a pair of composite kayaks that were stored temporarily in a tarp that was wrapped around the hull. The lumps were hard blister like bumps that did not move if pressure was applied to them. They were wrapped for several months after a house move.
The blisters seemed to be the effect of moisture getting in the layup somehow. I wasn't sure if it was moisture held against the hull by the tarp or moisture inside the hull, I suspect the former.
Anyway, they then went into a purpose built shed where they were totally dry, and the bumps completely disappeared and no evidence of them remains. I was working away from home for long periods so I don't know the time-frame for them to disappear.
It might be worth looking up GRP osmosis. It's not a subject that I know anything about, but your photo looks similar to online images of it. I believe it's more of a problem with yachts that are kept on moorings.
Paul-C is bang on. Knowing how it's occurred is something else. It could be caused by long term storage with water in the hull or laid up against damp grass. I've also seen it caused by poor manufacturing / incomplete curing of the resins. I can't be sure from the photos but it looks like it has occurred in areas that have seen previous repairs. If so, the best way to rectify this would be to grind back the gelcoat, ensure the moisture in the laminate is as low as you can get (Dry garage & dehumidifier), before attempting to re- gelcoat.
what you have there is a case of Osmosis. That is moisture has got behind the gel coat and is lifting it away from the material underneath. Most commonly caused by wet materials being left in contact with the gel for long periods.
It's more common in yachts that are left int he water for very long periods - not lifted out for the winter and not kept dry internally. Over time they will potentially become worse and potentially result in whole sections off gel coming away from the hull.
Generally it's a sand down completely dry out and re-gel to repair.
