Exterior Wood Finishes in the Desert
Last November, we began testing two coatings for exterior use here in Arizona.
With seasonal temperature swings of over 80°, humidity than can range from non-existent to rain forest levels, and a fair amount of summertime rain, our climate is a very challenging place for any exterior coating to endure. You'll see the harshness of the desert in the faded, dried and flaking finishes of many vehicles from the 2000s, or houses with peeling, faded and failing paint jobs. Wood, being a natural product that is highly sensitive to changes in climate, has always been one of the toughest surfaces to protect in our state.
Our basic test consisted of a simple cabinet door that was stained and finished with 2 coats of an exterior coating. The doors were placed face up on top of a wall where the were subject to full sun exposure and precipitation for the past 8 months. Most exterior wood doesn't see this kind of exposure, but it illustrated just how well these coatings could do under the most demanding conditions.
Mohawk 2K Polyurethane
Our first review of Mohawk's ISO Free 2K Polyurethane was published back in January (check it out here). We finished a table that lives on a back patio (and gets a fair amount of sun) in November at the same time we finished our other sample pieces. The table still looks great, and cleans up nicely every time it gets dusty. No scratches, peeling or failures of any kind.
On the alder cabinet door we also coated and tested as described above, the finish also looked great. It still has a great matte finish that cleans up well and shows no signs of wrinkling, crazing or any other noticeable blemishes.
We did not 6-side coat this door (requisite for maximum weather resistance), so we did see a few areas near the joints where the finish cracked as the door expanded and contracted. However, because you can also brush the 2K Poly, we plan on spot treating these affected areas after we prep them to see how touch-ups hold up.
We have no problem recommending the Mohawk ISO Free 2K Polyurethane for new, never previously finished, fine wood exterior doors. It is a bit more labor intensive to apply, and requires precise mixing, but it is certainly one of the best solutions for an exterior finish in a harsh environment.
General Finishes 450 Exterior Polyurethane
At the same time we were applying the Mohawk 2K Poly, we also finished a maple door with General Finishes' 450 Exterior Polyurethane. We were very excited to test a single-component coating that promised easy, fast and user-friendly application over nearly any substrate.
General Finishes has focused on the manufacture of industry-leading water based polyurethane coatings, wood stains and other specialty finishes for over 20 years. Their in-house formulations and unique resins have resulted in one of the most diverse and easy to use water based product lines we've tested. Though the manufacturer had not done extensive testing in environments with high heat and extreme UV exposure, were assured that the 450 Exterior Poly was up to the task of performing in the Arizona desert. And 8 months late, we're impressed with the results.
We completely coated a simple shaker door that was stained a dark color. Application was quick and sloppy by our standards; we just used a foam sponge to work the poly around the surface. However, we were very impressed with how well it laid out despite our less-than-desirable technique.
Because this door was completely coated, it did not suffer any of the issues we saw with the Mohawk 2K Poly. The door looks almost as it did the day we began the test. Minimal warping, and only a few areas where the plywood center panel had water work its way in from the floating joints around the edges. Certainly not any fault of the coating, though. Absolutely no water ingress or signs of failure around any of the joints.
Adding a "maintenance" coat is easy; simply give a quick scuff and reapply. For the price and ease of application, it's nearly impossible to beat the General Finishes 450 Exterior Polyurethane. This is a great product to use over newly stained doors or properly prepared, previously finished doors.
Both of these doors will be cleaned up, any defects repaired and put back out for another 6-8 month interval under the same conditions. From what we've seen so far, it looks like we've found a few solutions for protecting outdoor wood in AZ.