Many companies call their outdoor finishes: spar varnish. Not all of these actually are spar varnish but it is a starting point. The best finish will depend on the type of wood. I suggest visiting: www.woodanswers.com where you will get an answer to your question from finishing pro Michael Dresdner. To get the best answer include the type of wood, the name brand of your stain and what area of the country you live in.
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