Epoxy Barrier Coating for Exterior Wood

A woodworker reports success using clear penetrating epoxy sealer as a primer for exterior doors or boat brightwork. December 23, 2014

After many years of decent results with two part poly exterior finishes, we went to a new finisher using Euro-x exterior water based lacquers with poor results. As we try to get back on track, we are trying to decide between the two part poly, an epoxy barrier coat followed by varnish and a more traditional spar varnish on its own. Itís hard to figure as there are lots of designers wanting flat slab exterior doors.

Forum Responses
(Finishing Forum)
From contributor T:
Not knowing what your weather conditions are Iím in the San Francisco area and I have had great success with catalyzed urethane. I do a lot of exterior doors of many wood species and this finish holds up really well. I wonít use it in a total outdoor environment like patio furn but on semi protected areas like doors Iím really happy with its performance.

From contributor R:
People here are probably tired of my bit, but I do lots of exterior finishes as well as marine bright work. I've found that Smith's 2-part CPES under a good marine varnish is really quite good. I use a tung oil/ phenolic resin varnish both looks good and weathers nicely. However, after the CPES, one can use either WB or solvent based topcoats with decent results. Give it a try, it's impressed me.

From contributor J:
If you were asked to re-finish an exterior door, would you have to take it to bare wood? Or is a good sanding/cleaning enough to proceed?

From contributor R:
It is truly a penetrating sealer, so bare wood if you want it to penetrate. The wood soaks it up completely, so if it doesn't it just sits on top. Not what I would want or I'd use something else. It makes a good varnish last two-three times longer than normal, depending on how many finish coats and finish choice. It also makes a great filler when mixed with sawdust or wood chips. I've repaired large portions of rot in transoms and other areas of boats where proper repair isn't possible.

From contributor J:
To contributor R: Who makes the best varnish for topping epoxy that is repairable over the years as needed?

From contributor R:
I use a full tung oil/phenolic resin varnish made by U.S. Polymers. It's only available in 55 Gal drums, but I also use Epifanes that has some tung oil and some phenolic resin in it. High gloss only and thin it 10%-40% or 50% depending on the coat. If you don't want high gloss, tough, rub it out to the luster you want. The ones that have dulling agents just don't work as well. The Epifanes is available all over, try marine supply places if you can't find it where you are. Ordering is easy also, and cheaper. I've used it on a large live-edge slab mahogany dining table and rubbed it out with up to 8000. Looked great and easy to touch up or refinish. I use it on Adirondack furniture I make too, and get two-three years before touch up.