Clear Finish for an Exterior Door

No clear finish lasts long in the sun and weather, but here are some thoughts from finishers on the best of the bunch. December 15, 2005

We are finishing an exterior door made of mahogany. I would like to know what the best finishes are to use for the top coat (ideally it would withstand UV rays, and a Northeast winter/summer). The finish will either be sprayed from a Kremlin (that would be my first choice) or a regular siphon cup. The door is being finished here in the shop, so field conditions are not a concern. The second question is what to stain the door with. Are there stains that weather better outdoors (pigmented vs. dyes) and will these stains be compatible with the recommended top coat?

Forum Responses
(Finishing Forum)
From contributor O:
Just ask your supplier for an outdoor lacquer (varnish or whatever you love to work with). I don't work in the US, so I don't know names. Ask for an outdoor stain (it would be pigment mostly).

From contributor M:
I have my customers using an exterior waterbased coating that dries like a regular lacquer and holds up very well here in the NE. It's actually a line we import from Italy.

From contributor D:
I do a lot of exterior doors. If the door gets a lot of sun, it will not hold up past three years. If you use spar varnish, 1 year. Make sure you explain that to the customer. Dye stains don't work outside. ICA makes an exterior waterbased stain for exterior use. I don't use it because it's a pain to apply. I use Mohawk pig stain. It fades, so to slow it down I add some 844 colorant to my clear coat to act as a sunscreen - putting a couple of drops in your clear doesn't change the color that much. As far as waterbased exterior goes, I have tested four of them under harsh sun and weather - not one has made it a year.

From contributor J:
Chemcraft makes an exterior 2k poly called Lucido. I've had pretty good luck with that.

From contributor A:
Epiphany marine varnishes are perfect for exterior doors. They have the highest level of UV blockers of all the major brands of marine spar varnishes.

From contributor R:
I have never seen one last at all. If it was my door, I would keep a can of oil based stain on the front porch and a rag and wipe it down once a month. As for doing one for a customer, what does it matter what you use? It won't last long if it gets sunshine.

From contributor Y:
I have a gazebo with Doug fir posts which have McCloskey's Spar Varnish on them and after four years in California's sun, they look as good as new. One side of one of the six needs re-doing because a bunch of sap came through, but the rest are mint. I did cheat by mixing up my secret prep (thanks to Chris Minick at Fine Woodworking) of 1/4 pound of paraffin wax, 1 gallon mineral spirits, 1 quart spar varnish, and dye. It is the cat's meow. The mineral spirits dissolve the wax and drive it into the wood and the diluted spar varnish seals it, although obviously not against the sap coming out.

From contributor S:
I would use ChemCraft's D-Dur or one of the Cetol finishes from Sikkens. Alternatively, have a word with Sasco in Nova Scotia, who do all sorts of timber finishes for the northeastern climate. The boss-lady there used to be the laboratory manager at Sadolin in Denmark and really knows her stuff.

From contributor N:
ICA has the new LP157 series of exterior 2k pu's. I have had good feedback from customers so far.

From contributor B:
I'm currently in the middle of finishing three exterior mahogany doors and side light. This has worked well for me… I started with waterbased dye to even out wood, followed by thinned down (25%) seal coat of petit marine flagship varnish, scuff sand and synthetic steel wool. Then one more coat of varnish (thinned 15%, mostly to spray well). Scuff and synthetic wool and then glaze with an exterior stain to even the wood more and protect the dye. I'll finish up to a total of 8 coats (two a day with good weather) on the exteriors of the doors. The petite flagship really ambers, which will also protect (they state they have the highest amount of UV protection in a marine varnish) the glaze and stain. This has worked very well for me in the past. But as stated, in heavy sun, three years would be great.

If you have a lot of time to get this project out the door, another option would be to first seal the door with a marine epoxy (followed with several coats of high grade marine varnish), as this will stabilize the door, which minimizes wood movement that contributes to the finish breaking down.

From contributor D:
The problem with epoxy is that it turns white from UV. Now, you can say the marine varnish will take care of that, but the finish will have to be removed in less than 3 years and the epoxy will not come off.

From contributor B:
The epoxy sealer (multi wood prime) I would use doesn't turn white from UV. It's an almost water thin and water clear two part epoxy sealer/primer. Combined with a high grade marine varnish, it's a very durable finish.

From contributor S:
One thing to remember in all this is, what's the customer going to do in 3 - 4 years' time? Building up multiple layers of spar/marine varnish and epoxy varnishes may increase the durability of the initial finish, but how do you maintain it without taking the whole door and frame back to the shop? At least with Sikkens Cetol or similar exterior stains, the maintenance can be done on-site by the owner or a decorator.

From contributor B:
I assume they would clean it, scuff sand it and apply a coat or two of the original varnish. This epoxy sealer product doesn't really build up. It literally gets sucked into the wood. I've never had to strip any of the projects I've used it for (I've only used it a few times), but I seriously doubt you would have to take off anything other than the topcoat.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor H:
We have a cedar clad home in the North East Victorian Alps, Australia. The damage from sun exposure to any finish is a major problem here . We have coated our front door and the cedar window frames with a transparent water borne exterior 2 coat finish and it has lasted 4.5 years. The door is still excellent, and the window frames need recoating now. The product is called Intergrain DVD and has excellent UV and water resistance, but is not suitable for previously oiled, hence the need to redo the window frames.