Clear Exterior Door Finish that Won't Alter Wood Color

This post from a woodworker looking for a clear finish for exterior doors that would preserve the color of some beautiful Mahogany doors drew some interesting and detailed responses. April 15, 2012

I am refinishing a solid Mahogany entry door and side panels. After removing the old poly and stain I have sanded it thoroughly and the different tones of Mahogany have appeared. The homeowner and I think it looks beautiful and we have decided to ditch our stain and poly plan and go with a clear. We understand the color will be uneven. The door is well protected from water but the lower half of it gets late morning-evening sun. I wash her house once a year so yearly upkeep is definitely an option and she would be willing to wash in-between also.

I am confused and have read all kinds of things to use such as Sikkens Door and Window, marine grade poly, boiled linseed oil, tung oil, etc. What can we use that will best protect the color of the wood, not necessarily last the longest or have the least upkeep, but keep the color true without repeated full on refinishing?

Forum Responses
(Finishing Forum)
From contributor Y:
If you are concerned about sunlight, weather, and durability the best thing to use is a UV Automotive Acrylic. We use this on all of our high end exterior products. It is not as durable on wood as poly for long term but will hold to about 75% of a poly finish life span. You will receive a superior sun bleach and fade resistant coating. Just don't forget to seal the top and bottom edge of the door with three times as many coats as the rest. The door can be waxed as needed to heighten the lust and extend the life of the finish with any automobile hand wax.

From contributor M:
To contributor Y: Can you qualify your endorsement of using an automotive product on wood? I'm just looking to hear your experience with these finishes - is this a mainstream application for you (exterior woodwork)? In other words, just how much have you been doing using auto finishes and for how long? I've been following threads on exterior finishes for years here, and have not yet encountered this approach.

I am also about to begin (fabricating) three mahogany exterior doors, sidelights and transoms and am also in a quandary as to which finish to use. I've built hundreds of exterior doors in my shop, but this will be a first that we will be applying the finish - all previous work was supplied unfinished.

My situation is slightly different as two doors are shaded under porches, and the third door is on a north wall with just a little sun early in the mornings. I had just about settled on using the Sikkens, but am now interested in your application of automotive finish. Iím just a bit leery as wood is a whole different animal than metal when it comes to movement, expansion/contraction, and moisture content.

From contributor R:
I'm not experienced with doors and windows, but I have about 30 years of experience with Brightwork on boats. I donít like Sikkens Cetol and do not use it anymore. I have no experience with Door and Window.

I use a phenolic resin-tung oil varnish and get as good as, or better results than Cetol. Boats take a lot more sun and weather than front doors, so that's what I would use, but I'd like to hear from Contributor Y regarding what works well for this application. I thought automotive finishes were a lot less flexible than wood finishes. Is there any problem with cracking and flaking due to the movement of the wood?

From contributor M:
To contributor R: Do you have a brand name for the varnish you recommend here?

From the original questioner:
Contributor Y - would you mind elaborating on the UV Automotive Acrylic process some? What sheen will it come out, gloss? With frequent cleaning and waxing how long would you estimate this process would protect the color of the wood before needing to be completely refinished from sun bleach?

Contributor M - I had about settled on Sikkens Cetol Door and Window clear satin. I do not like the plastic look so much but Sikkens expands and contracts very well (Cetol 1 and 23 plus do not), is very easy to touch up, and easy to apply. However, being it is only clear I am very wary about how much U.V. protection it will provide, even with several coats.

Contributor R - would you mind also elaborating on the phenolic resin-tung oil varnish process? I'm not certain what it is or how it works, what sheen it will be, what the maintenance is, and how long with proper maintenance would you expect it to keep the color true before needed total refinishing?

I cannot stress enough that my concern here is protecting the wood and especially the color. I'm looking for something that will do this for years to come with proper maintenance, even if the maintenance is frequent, without have to take it all off and completely refinish it.

From contributor R:
I use a 100% tung oil-phenolic resin varnish. Regrettably, it isn't available retail and commercially only in 55 Gal. I have, however, used Epifanes Clear Gloss. It isn't 100% tung oil nor solely phenolic resin (it has some alkyd resins), but it is a very nice finish. You'll need at least four coats, I prefer five-six.

I sand between coats with 320-400 W&D. The first coat 50/50, second 70/30, the rest about 90/10, sometimes 100%. It is tough to spray; not so much application, but overspray makes everything incredibly sticky, but it can be done. The biggest drawback is dry time (I sometimes add some extra drier). I've found the single most critical factor in application is the quality of the brush. Badger is the lowest quality brush I use for varnish. I can't think of anything else at the moment.

From contributor R:
When using varnish, I always use a high gloss and put on several coats. (Satin or semi-gloss varnishes just have fine particles that occlude the look of the wood and mess up the hardness) If I want a satin finish (or any lustre, even gloss) I just rub it out. I don't rub out railings, but any furniture I do and sometimes boat interiors (which are often mahogany).

Regarding maintenance, most boat owners do their brightwork every year or two. I'm thinking you might get two, three, or maybe more on your door. If you don't let it go too long and don't let the finish fail down to wood, you can just sand to clean and re-coat with a couple coats at70/30.

If it fails, then you will need to sand to bare wood and recoat three-five times. The trick is to not let the varnish coats fail. I get two-three years pretty consistently on yachts, work boats not so much. Two part LP is better for them. Something else I do on older wood (sometimes even new) is apply a 2-part CPES sealer coat before varnish (itís easy, and also makes refinishing easier).

From contributor J:
I have used Sikkens Door and Window, and I have used Epifanes gloss and satin varnish. Use Epifanes. If you take the time with Epifanes, first three coats thinned, fourth and fifth coat at full strength, then a last coat of Satin, there is no other finish that will compare. You have to be patient. It will take a week to produce this finish.

You could try MLC's Euro X, but you need to follow the products instructions for mixing very carefully. It's a 2K exterior poly that is almost bulletproof. Not sure about longevity and re-coating in the field.

From contributor Y:
Although we do not do a great deal of exterior product these days, I can say that Automotive finishes can produce great results on wood, and the harder the chosen material the better. This was requested of me back in the early 1980's on some exterior rail and fret work at Avenel Country Club in Potomac, Maryland. This is a PGA facility.

Although the use was a more than an unusual request as I am sure you are aware, and the application had some strange effects to me as a finisher, the end product was truly beautiful. The coats required a slow thin build up, and the first two produce a gritty crystal like surface to sand. The overspray from our turbine sprayer produced a silly string effect as it dries as fast as it passes the applied surface. The finish produces a luster between what you would consider gloss and semi-gloss. I have never had a complaint from a customer and I do use this application on all exterior doors.

I am located in PA and in 2009 we finished a large scale interior project just outside Park City, Utah. We were asked by the homeowner to apply a decorative finish to their solid cherry exterior doors. We applied Permalac Automotive Acrylic Lacquer. As you are aware, the weather conditions in the mountains of Utah can go from desert conditions to subzero with extensive high altitude sun exposure. I have never had a complaint.

I can't tell you that it is the norm if that is what you ask. I can tell you I have had great success with these type of finishes for exterior applications over the years. I have been applying decorative finishes for 30 years and can honestly say that there have been many occasions that I have looked outside the proverbial box for better solutions.

From contributor R:
To contributor Y: Were you looking for anything special in your choice of an automotive clear coat?

From contributor C:
I'd also vote for Epifanes, and add Bristol Finish to the suggestions.

From contributor Y:
If you are referring to our Utah Project, yes we were looking for something specific. Since the project was a considerable distance from our shop in PA I spent the weekend doing my due diligence online to look for a product that I could get locally within a two hour drive distance and one that the manufacturer listed wood as a component.

Permelac was available regionally at our location. We ran a test finish on site on a piece of the cherry trimwork. We placed it in the midday sun along with a piece of the "UV Coated" Brazilian cherry floor from the flooring installer. We covered half of each. The property sites on Mount Ogden at 7,000 feet so the sun is quite intense. The following day the flooring had changed about ten shades from exposure while the trim piece remained consistent.

I am only here to pass on my experience. Do your research and always test for yourself. As for us, it only seemed a small leap of faith that an automotive acrylic would sustain the elements. To my experience, it has. When the circumstances were prevalent we have had good success without the sub material looking like plastic.

From contributor R:
It doesn't sound like the automotive option is something most people would be able to do themselves, so if it's a do it yourself thing, go sealer and varnish. If done professionally, I might try the auto finish. On rethinking this, I would use the sealer coat with CPES first. I use Smith's and find it easy to use and works well. I think it forms a better interface with the varnish and will give longer life to the finish. It also gives excellent interface with the wood and sealer strengthening the entire bonding process.

From the original questioner:
It sounds like Contributor Y's recommendation may be closest to what I'm looking for. He said, "The following day the flooring had changed about ten shades from exposure while the trim piece remained consistent." I am not really interested in how long the finish will last; I am only interested in finding a finish that will prevent sun bleach, even if it's a high maintenance product. There are many good and some excellent coatings out there that hold up really well but they just don't prevent sun bleach. If the coating needed to be maintained twice a year it wouldn't bother us a bit as long as the coating prevented the wood from being bleached.

From contributor O:
You or your client will be interested in how long the finish lasts when it comes time to strip and redo the door and itíll be a real pain. I like an easy finish that can be touched up without a lot of messy stripping and scraping, but thatís just me. Think about it before you commit.

From contributor Y:
Please do your own sample testing if you are leaning in this direction. As I said, we have had a good deal of success, but you must sample the outcomes for yourself.

From contributor K:
Epiphanes and like varnishes take forever and are very yellow, although a great UV product. Iím surprised no one brought up urethane clears (for wood) as I often use it for exterior work. It dries quick, hard, and durable and can be buffed to an amazing gloss.