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You can make it waterproof - sort-of, but all exterior film finishes require maintenance in order to look good over the long haul. Most spar varnishes are junk, certainly any that you can buy at HD, etc., so that includes MinWax, Helmsman, etc. I know some will disagree with me, but those products just don't stand up well if exposed to the 4 seasons of sun, rain/snow, and temp. changes. If the furniture is going to be on a porch, etc., out of the rain and direct sunlight, then those products may work pretty well.
The arguably best outdoor varnish is Epifanes Marine Varnish. I have a bench that I made 5 or 6 years ago that I used it on and it still looks great, although I have had to give it a refresher coat or two every couple of years. Epifanes says you should do it EVERY year. You can buy it at West Marine and on the web and it costs about $40/qt, and requires 7 coats if you follow the directions, the first several coats thinned different amounts. All in all, it's a pain to use but the results are great and it lasts longer than any other easily available exterior varnish. The key to it's performance are the UV stabilizers it has to prevent UV light from degrading the varnish. But over time those inhibitors break down - hence the need to apply a new coat or two every year. If the furniture is going to be out of direct sunlight, you might very well not have to add any new coats for several years.
Some other folks report excellent results with GF's Exterior 450 Poly. It's a waterbased product and a whole bunch easier to apply. I've never used it, however, so I can't compare it directly with Epifanes.
John
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Thank you I will check it our.
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John nailed it (no surprise), the box store spar varnishes are made almost exclusively with urethane resins which just don't do well in the outdoors. The true marine spar varnishes are a great choice, but I also want to suggest consider exterior untinted paint.
More info here.The link goes to a slightly dated article that explains it a little better. But consider that since oil based paint is getting very hard to find, at least one member here (Cian, I believe) has used the SW exterior acrylic A 100, and it seems to be just fine as well. But don't overlook the caution John mentioned: any exterior clear finish will need maintenance, you won't find a lifetime solution. [url=http://www.askhlm.com/Articles/ArticleViewPage/tabid/75/ArticleId/26/Paint-On-A-Clear-Finish.aspx][/url]
I started with absolutely nothing. Now, thanks to years of hard work, careful planning, and perseverance, I find I still have most of it left.
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We used to use two part varnishes on the boats that you mix up like epoxy. They would outperform and last much longer that any single part varnish. Jamestown distributors has a few different kinds.
http://www.jamestowndistributors.com/use...rt+Varnish
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This is why I posted my question here. Lots of excellent replies. So far I like the two part epoxy description. Yes it is a lot of prep, but I suspect my grandson will not pay to much attention to how the pieces are action until late in the finish's life.
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09-22-2016, 05:19 PM
(This post was last modified: 09-22-2016, 05:22 PM by bhh.)
(09-21-2016, 08:22 AM)joe1086 Wrote: I've used the clear paint on a south facing mahogany exterior door...applied seven years ago and still looks great.
Edit, oops, sorry, missed Fred's link.
The original article on this technique (and demonstrating Minwax Helmsman is just terrible)
http://www.askhlm.com/Articles/ArticleVi...inish.aspx
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Thanks for giving such creative ideas to use outdoor furniture