Varnish blister?

[braidmike]

Here's one I haven't experienced before: in two places on the exterior woodwork (one on the toe rail and one on the inside of the cockpit coaming) there have appeared 1 1/2" blisters. The varnish swells up with air and looks just like a blister from poor fitting shoes. It happens on warm sunny afternoons. I'm assuming it is due to moisture under the varnish, but this is a first-time occurrence in over five years of ownership of this boat in the same environment, with the same Epiphanes varnish applied every 4-6 months.
Has anyone seen this?

[tager]

At least you know that your varnish is a good vapor barrier!

[CamD]

Those blisters are likely caused by painting in direct sunlight on a hot day. The varnish skins over and dries trapping wet varnish underneath.

[DwayneSpeer]

Yes, I have. Unfortunately it's time to get out the old heat gun and remove the old varnish. It has lost it's hold on the wood and will only get worse with time.

[braidmike]

Thanks for the ideas...
It is almost time for the spring re-coat, it will have a bit of extra attention in a few areas. I think you are correct Dwayne; the blisters look like its all the way detached from the wood. Hopefully a complete removal of that area plus an inch or so will suffice. If not, well there's another six week project to add to the list!

[karlhead]

This has happened to me also. I'll bet that when the first coat was laid it was a very warm day and perspiration dripped of off your nose onto bare wood. If a drop of moisture lands on already laid dry varnish and you hit it with the brush (especially foam) it will turn into a bunch of tiny droplets and very tiny bubbles. On dry wood one must be very careful and use a tac cloth or non -lint tee-shirt material.