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Martens
06-30-2001, 11:47 AM
Can anyone advise using any varnish over epoxy coated wood below the waterline and continuously in the water for up to two weeks without deterioration? If so, please mention the varnish.

I'm ready to put a polyurethane paint finish on my pram's hull but would consider varnish or Cetol if there's a good chance it will stay on.

Many thanks!

Gary Bergman
06-30-2001, 01:50 PM
I don't know if this will help or not, but I Cetol'd the centerboard in one of the dinks and it sits in the water for months on end. Hasn't came off yet.

thechemist
06-30-2001, 09:17 PM
Two-component polyurethanes will peel in a couple months or so if continuously immersed. It is a technical thing having to do with molecular structure and other matters.

Occasionally wet, rained upon, this does not affect them.

As for the adhesion of varnish to a cured epoxy surface, this is determined by the adhesion developed between the varnish and the epoxy. Varnish applied on top of fully cured epoxy prodcuts develops little to no chemical adhesion. Mechanical adhesion will fail in days to months on immersion, depending on the molecular makeup of the two materials. Varnish applied on top of partially cured epoxy products may stick very well, or may not cure at all, depending on the particular product and, in some cases, mixing-ratio errors with various types of epoxy products.

If you search [upper right] for threads in building/repair with CPES in the title, you will find a variety of experiences with that product that suggest it may be what you want, as an adhesion-promoting primer for varnish. Searching for other threads with the words varnish and epoxy in the text will get you too many, but there has been a great deal of discussion about various epoxy products that do good or bad things in conjunction with varnish. You should find it entertaining. Have a very comfortable chair before starting.

Martens
08-03-2001, 09:01 AM
Follow-up to Gary Bergman and The Chemist:

Your comments were most helpful. I used Interlux Brightside polyurethane on the bottom and Cetol on the sheer planks and inside, both over epoxy saturated wood. The dinghy was towed for a couple hundred miles over a period of about 3 weeks and remains in good shape today with no deterioration of the finish.

Thanks again!