Replies

1. 
   mvflaim | Aug 15, 2007 05:05am | #1

   I have always wanted to try to coat an outdoor project with fiberglass like boat builders do but I have no idea if it would work. Other than that, I'm not sure there is a finish that will protect against the suns UV rays.

    

2. 
   SteveSchoene | Aug 15, 2007 01:31pm | #2

   While the manufacturer says Defthane is an exterior finish, and even brags it could be used on above water marine applications, this is just plain not true unless the boat is stored indoors. It won't be hard to find a better finish for outdoor furniture.   Single part consumer grade polyurethane varnish just can't hack the sun light and is very vulnerable to UV damage. 

   That said, there is no clear finish that will protect outdoor wood without regular maintenance.  Opaque finishes can last dramatically longer without recoating. 

   If you just have to have a clear finish your only choice is to use a marine grade spar varnish.  This means one of three products--Pettit Captain's, Interlux Schooner, or Epifanes Clear Gloss.  These will cost $25 per quart or more.  You can undercoat with epoxy resin to add resistance, but epoxy is also very vulnerable to UV and must be overcoated with a UV protectant marine varnish. 

   With marine finishes you need to follow the manufacturer's directions.  This means at least 6 coats of brushed on finish, scuff sanding between coats.  Total film thickness counts.  Then you must add a "refresher" coat periodically.  This  usually means annually if the item receives full sun.  Any slight dulling of the gloss is signal to recoat.  Any dings must be patched quickly.  And, after 5-7 years you are likely to see signs of failure as the finish starts to lift--you see yellow opaque patches--and you must strip to bare wood and start over. 

1. 
   shopdoc | Aug 16, 2007 03:53am | #3

   Steve Have you ever tried Hydrocote Polyshield? A friend recommended it to me about 15 years ago and I tried it on a picnic table that was exposed year round to the elements. The results were amazing after 5 years it still looked great but I took it back to bare wood and reapplied the Polyshield. When I gave it away 3 years later it still looked good. Since then I have used Polyshield on every exterior door that I built with excellent results and never a call back (probably close to 50 doors!). My own front door, built with quarter sawn white oak, has Polyshield over dark walnut stain and after 4 years it's needing redone because the stain is fading though the topcoat is still in good condition. Give it a try you'll like it.
   Steve