Sunday, November 25, 2007

Best Finish for a Natural Wood Door

This is a post from one of my woodworking forums - the discussion was on finishes for a natural wood door and how they never last. This post is about an alternative to using spar varnish and the like and I thought I would share it because I thought it was quite good:

Posted by Jim Kull:

"As a preface, allow me to set the stage. Almost daily there is a posting about clear, exterior finishes for doors, chairs, signs and such. Responses run the gamut from diehard marine finishes to apply a coat of primer and then paint. Each of these has a bit of a problem. Marine finishes are not always the easiest to find and it grieves me to think of a lovely oak, teak, mahogany, fir, redwood or similar nice wood door painted in mauve goop.

Bob from Florida inspired me with his continuing and accurate statements about the failings of a clear coat and the advantages of a good quality exterior paint. I decided after lots of reflection that he really was right but there was always the picture of mauve in my mind. Sooooooooo, how could one take advantage of his advice and yet capitalize on the beauty of a nice wood.
I began to reflect on the characteristics of paint. Now, comes the boredom.

There were several things I knew about paint. Exterior paints contain a mildewcide and a fungicide that a varnish does not. The best quality paints will contain a UV protectorant and trans-oxide pigments in very high percentages. Almost all paint is custom mixed by the store. The retailer maintains a large supply of base products that are used to achieve the desired color. There are generally 4 base products and the specific one for your paint is determined by your color choice. These base products are either named or numbered. They are named pastel, deep, tint and neutral. If numbered it is cleverly 1, 2, 3 and 4 with the exception of Olympic who numbers 1, 2, 3 and 5. Olympic is unaware that 4 comes before 5. Pastel and/or 1 is virtually a pure white and used for the lightest of colors. The others are slightly color altered from white and more translucent than pastel. These are used for succeedingly deeper colors. All of this comes to neutral, 4 and/or 5. These are clear and used for the darkest colors. In the can they are somewhat opaque but dry more or less clear.

Now comes the testing. I bought 4 oak exterior doors. Each door was given one coat of the same MinWax Stain. On 3 of the doors, I applied 2 coats of "paint" to the 6 sides of each door (3 coats on the top and bottom edges). Each of these three doors had a different type of exterior neutral, 4 or 5 base. The fourth door was finished with a common spar varnish from my local friendly paint/hardware store. The bases for the 3 painted doors were an exterior semi-gloss acrylic, an exterior semi-gloss oilbased polyurethane floor paint and a semi-gloss oilbased trim and siding paint.

The doors were set up, slightly inclined, in mostly direct sunlight under a pecan tree in the backyard. My wife just loved that one. Daily, the sprinklers managed to hit the doors. The birds in the pecan tree used the doors for target practice. And, yes Steve, the dogs did anoint the doors on a regular basis. My blonde Cocker, Zazu, was particularly enamored with the doors. Over the course of the test the doors experienced lots of Texas sunlight, rain and snow. The temperature went from below freezing to over 100. The advantage to the inclined position of the doors was the snow, ice, water from the sprinklers and the rain tended to collect in the raised panel areas. I feel these doors were subjected to far more severe environmental conditions than would be expected from normal use.

The results were interesting. The spar varnish looked fabulous but after about 2 weeks it began to develop small cracks. In rapid order the door began to turn black, started to mold and the smell was enough to knock a buzzard off of a manure wagon. The waterbased acrylic is milky in the can like a waterbased poly. It dried to a more or less water clear surface but was a bit cloudy. It tended to wash out the stain a bit. Over time it became cloudier and ultimately become almost white. But, it remained solid and protected the wood. The oilbased bases are also a bit opaque in the can but dried to a clear finish that is almost identical to a spar varnish - they added an amber tone to the doors. Both the poly floor paint and the trim and siding paint remained "clear" over the entire test period.

The testing came to an end with a bit of encouragement. My wife said something clever like, "Get those damned doors out of the backyard!". She does not understand science. The floor poly had some minor checking and a thinned coat of the same base over the surface made that disappear. The door with the oilbased trim and siding paint was perfect other than it had lost a bit of the gloss.

So, I am with Bob - paint the door. My preference is the oilbased products. If you are predisposed to a waterbased use an acrylic rather than latex.

One thing you will find when you go out shopping for your product is a lack of knowledge on the part of the salesperson. Not many of these folk are aware that their neutral or 4 base will dry clear. If you want to have some fun, spring it on them. They will suggest you are full of Donkey Dust. Ask them to shake a can and put some on a stir stick. Dry it and voila, it is clear."

The Sherwin-Williams # is 6403-25767(gallon).
I have found that thinning helps a lot. Test on some scraps before hand.
I have been happy with the results.

End of copied post. John


Jim W said...

Thank you for doing that test. Sounds like something I'd do. I am touching up and re-varnishing an oak stained front door on a sun wall for at least the third time in the past 10 or so years and am looking (again) for a better finish. I have always ended up finally submitting to the old satin Helmsman spar varnish that I know won't hold up but have never found anything else. I have never heard of this before...using #4 base paint. I didn't realize it actually dried clear. I am going to check it out tomorrow. I'll let you know how it turns out.

doorman said...

Before you apply the spar varnish it would be a good idea to put a couple of coats of Smiths clear epoxy sealer on first.

doorman said...

When it comes to finishing exterior doors do as the boat builders do. They apply several coats of clear epoxy to all edges and faces of the wood before applying the exterior varnish. Then they put multiple coats of varnish on. There is no such thing as too many coats. The more the merrier. Just make sure you let it dry between coats per manufacture recommendations. Interior doors of course do not require such an extensive finish. But they still need to have some kind of finish on them to keep the humidity changes inside your house at bay.

Robert said...

This is all very interesting for the techies out there but I prefer on good external oak to use TUNG oil 50% diluted with white spirit. Thats all, no undercoat, nothing, just the oil. It looks great, dries really quick and looks good after a really bad winter in the UK. You might need to do a light sand and recoat in the spring but its takes no time at all. I use a cloth to apply it.

Anonymous said...

Does anyone have long term results from the #4 base paint? From John's control study, it certainly sounds like this will last a long time but I'm curious for real results over the course of a few years. I too went to my local Sherwin store and stumped the guy behind the counter. The base dried to a nice clear though just like it has been told!

kate said...

Just found your blog and have a further question, please. I have been using the Helmsman and it is not holding up at all. If I go to the base paint, do I need to strip the Helmsman off or can I just sand and coat with the paint?

Anonymous said...

Hi my name is pete T. Ive been using Muralo industrial coating clear base no pigment on spanish ceda. comes out beautiful. High gloss only, Im anxious to see what a couple of years will bring , on exterior doors,sea side maine the paint store workers wont comment either way . I think they are trained to say nothing.

Stu said...

Regarding the Sherwin-Williams # is 6403-25767(gallon), would this provide UV protection, and how many coats to attenuate UV that would damage the wood fibers?

John Eaton said...

As the article explained, the failure of film finishes occurs due to moisute eventually getting through the finish, which allows mold and mildew to form under the clear - you'll have to check the UV blocking effect as I'm not sure there is very much. I'm not sure how you can block UV as even finishes with inhibitors are minimal at best - as with anything, your results can vary depending on where you're located, the relative humidity (with changes), proximity to water, local weather, etc...