I’m making an exterior door and window unit from very expensive clear douglas fir and have finished the finishing process on the raised panels. Ignoring most of the advice I got here, I used a new water-based outdoor urethane product (see title). I used this product because I’ve been a little too asthmatic lately to keep using spar varnish and spar varnish is hellish anyway. Also, the application is not too demanding given that it is on the North side (ALL rain here comes from the South (almost)) and is protected from sun exposure or I would’ve used spar varnish.
I used Watco (2 coats) to harden the wood and gain some depth of wood grain. Then, a Zinnser seal coat shellac layer, then six coats by brush of the water-based urethane. I sanded between each two coats with 320. Even at about 60 degrees, I could easily get two coats in an afternoon waiting for about 2 to 4 hours between coats. The finish brushed well and I’m not an enthusiastic brusher.
After three days of curing the last coat at about 60 degrees average temp, I sanded with 320, 400, and 600 with wood blocks first, then lightly by fingers. Then, I used green and white artificial steel wool, waxed and buffed.
While finishing, I left a day between pairs of coats with sanding (320 grit) before the next pair of coats. All the way through, sanding mostly produced dust, not wormlets, except in the few places where I left drips and sags.
Time will tell how well this stuff performs in the out of doors, but it worked well and rubbed out to a nice polished satin finish. I’m quite satisfied so far.
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Please keep us posted on how it holds up. Water based varnish that holds up to the sun would be a real find.
I hope it works out well for you, but I have my doubts based on two things. Waterborne, and polyurethane. I suppose it could be possible to make a waterborne product that will withstand the rigors of full exposure to the elements, if and when this product is made it won't be made with polyurethane which is very susceptible to UV ray deterioration.
Rob
I'm not familiar with Varathane's exterior water-base product but I do know there are some fine exterior water-base finishes (e.g., Target Coatings Polycarbonate Urethane). And contrary to popular belief, not all urethane resins perform poorly in exterior applications. Take the finish on your car for example. Auto finishes are most often a paint topcoated with clear polyurethane. It's the type of resins used that give it such a long service life in such harsh conditions. As another example, a finish called Five Year Clear uses a penetrating epoxy followed by an exterior oil-base polyurethane that performs exceptionally well; hence the name.
The known problem in your schedule was the shellac. It's not an exterior finish, even under 15 coats of exterior varnish. I understand your desire to use a barrier cost between the Watco and water-base finish, but if you had allowed the oil/varnsh mixture to cure enough, you would not have needed it. Using the oil-base finish to bring out the warm tones in the wood under the water-base finish is a good idea, but it doesn't harden the wood; that's just misleading advertising.
finishwiz.com
Telemike,
A couple of points, first if you use shellac it's harder than watco, it seals and make the grain pop beautifully. Second I'm terrified of water based anything for durability. I'm a real tradionalist and would have used epiphanes
I understand your asthma and would have simply put on a good mask to protect my lungs. Yeh Epiphanes is some foul smelling stuff especially when you heat it as recommended. but it is the most durable varnish I've found..
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