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