Paint Blisters

[Jeff Benagh]

[as a followup to my poorly framed question yesterday, re: bottom paint]

Is it normal to see blisters in paint under the waterline on a plywood dinghy after a summer in the water? If not, how to prevent them? If so, how often do I need to repaint before I get concerned?

My epoxy-plywood boat had some blistering of the paint on and near the skeg, along with slight discoloring of the wood underneath. I plan to sand down and repaint but am not sure if I should worry (obsess might be the better term ;) Some of the older advice could be summarized by "bottom paint" but I fear that I may have a more fundamental problem and next year might be sanding down bottom paint...

Jeff

[Tonyr]

Jeff, you asked "Is it normal to see blisters in paint under the waterline ".

The answer in my experience is that if the paint is neither formulated specially for bottom use, or is not a two part epoxy coating, it will blister. Presumably some (all?) two part polyesters will work too.

The anwser seems to be that one can only use "ordinary" paints below the waterline if the boat is dry sailed (launched from a trailer each time out).

Anyone with contrary findings?

Tony.

[Todd Bradshaw]

That's pretty much the story. If it doesn't say right on the can in plain English that the paint is suitable for use BELOW the waterline and you leave the boat in the water for much more than daysailing-type usage, you may well be looking at paint problems happening. A paint that will withstand extended periods of immersion is a big plus from a marketing standpoint. Believe me, if a particular boat paint will do that, they're going to advertise it that way.

[NGrace]

Hi Jeff,

I restored a 12 foot lobsterman's skiff last summer that was marine ply covered with glass and epoxy. I put Ditzler primer over the epoxy and then two coats of Parkers. If you can, look into a primer/undercoater like Ditzler or another two part epoxy paint and use that. I am happy with the Ditzler, but it is pricey stuff.

Best,
Nathan