> Suppose you were to be building a stripped deck, but weren't putting epoxy
> down on it. It was just bare wood. And of course you didn't want it to get
> waterlogged. Is the varnish enough, or is there a better material? Heck,
> would polyurethane work?

In building my current work-in-progress, a skin-on-frame kayak, I started to waterproof the frame pieces with epoxy resin, which I painted on with dosposable brushes. As the days were hot I mixed small batches, and trashed a lot of brushes. This upset my frugal nature, so I stopped about halfway through the process. The next day I went back to my task with varnish, which had a far longer pot life, and a bit shorter drying (versus curing) time. For a while the two coatings were nearly identical in appearance: nice and shiny. That project took a few detours -- no, wait, make that MANY detours -- over the past three years. During that time the frame sat on my deck, or on trestles in the back yard, sometimes under a tarp, sometimes wrapped in Saran wrap, sometimes out in the sun. It got a little rain and snow on it at times. In short, it encountered a typical Chicago winter, twice.

The net result: The spots where I used resin are now VERY clearly identifiable. They look beautiful. The spots where I used varnish are also identifiable. They look like they need another coat or paint, or two. Plywood frames that were covered with varnish had lost a good portion of that finish, leaving exposed wood, which soaked up moisture, and may have weakened the frames, but not so much that they were unusable. In a few areas where moisture was trapped by the Saran wrap there was some mold growing on pices of plywood that had been varnished. Cedar stringers for the frames were a nice yellow color where they were covered with the epoxy, and a weathered gray where they were covered with varnish.

Conclusion: I wouldn't recommend varnish for covering wood that might be immersed in water for several days. If I used varnish at all I would set up a repair/repaint schedule to keep the coating solid. Chips, cracks or dings let the water get in under the varnish coating, where the moisture seems to help the varnish flake off. Again, the epoxy had no such problems. My suggestion is to seal the wood with epoxy. Varnish on bare wood doesn't seem to be very good over time.

Those areas where varnish was applied over the epoxy looked fine. The wood looked good, and the varnish was holding on nicely. I could not tell the difference between them and areas of epoxy that were NOT coated with varnish, so the epoxy has not had any apparent or noticeable damage from UV over this time.

I haven't tried urethanes or polyurethanes. Maybe I'll do so in a year or two. Can you wait for those trials?

Hope this helps

Paul G. Jacobson