Most Durable Finish for Exterior Door

[thesource]

I'm building some Sapele raised panel doors. If anybody has suggestions on the "best", ie. most durable finish, they would be greatly appreciated.
One will face east, but two others are unprotected from sun or rain, on the south, and west sides.
Thanks in advance.

[dancam]

I installed two exterior doors (2 years ago). They were Philippine Mahogany. I got them unfinished and I finished them with three coats of Sutherland and Wells tung oil. I made sure to do all surfaces, i.e. top/bottom edges as well as underneath the hinge hardware. I let this dry for a couple of days between coats and then I put on a coat of Penofin Marine Oil w/UV protection. I let this dry two or three days (sanded between all coats w/3M Grey pads) and then top coated this with two coats of Mccloskey' Man-O-War Spar varnish that also has UV protection. This was the exterior side treatment. The interior had the tung oil and Minwax satin poly (3 coats tung and 3 coats satin poly).

Both doors face North and are exposed to some driving rain (when we get it) and they have held up beautifully.




Dan C.

[gordonmt]

I tried three different types of finishes on my front door including spar oils and urethanes. Some worked better than others but on a front door exposed to direct sunlight, nothing worked very well in the end. The environment was just too harsh.
I eventually stripped everything off, primed it with solvent Kilz, and then painted it with a oil based paint. It has been perfect for over 10 years now. It's not as pretty as a finished door, but it does last now.

[Gofor]

For direct sun exposure, no clear finish has yet been proven to stand up to UV penetration to the underlying wood for a long period. Even the best start failing to some extent within a couple years. In the Northern climes where the sun is not as direct, some silica based coatings will last for a couple years longer. Some of the most touted deck coatings include this, but if you look at the tests done, they are performed in Canada or southern Australia. They work as advertised in those climes, but used closer to the equator, the manufacturers all recommend their pigmented versions. "Spar" varnish (or long-oil, meaning the molecules are longer chains) are the most durable of the clear or translucent coatings. Sadly, the only long-term protection is to block the sun from the wood, which means pigmented coating and means you cannot see the beauty of the wood.
Good quality gloss paint is the best for long term (5-10 years) sunlight protection, with white color being the most durable. Semigloss will come in a close second. Darker colors will weather faster, as they absorb more of the harmful UV, which breaks down the binders (resin) that holds the pigments in place. The wood is protected from sun until the pigment is deteriorated to expose it, but moisture will penetrate the resin before that happens, and will damage the wood unless it has natural moisture-damage resistant characteristics. I have no idea what weathering characteristics sapele has.
We have all seen or seen pictures of beautiful teak and mahogany wood on vintage boats too large to be sheltered. This is achieved by annual or bi-annual restoration of the wood finishes. Its a matter of how much maintenance you wish to put into it.
The south facing door will have the most UV exposure, west second and east third. North facing doors here see direct sunlight for very little if any of the year.

Go

[ebarr]

I remember reading an article in one of my countless mags a few years ago.

I believe the best was a marine grade finish from a boat supply store. I see if I can find the article.