Automotive Clearcoat for an Exterior Door

Some finishers say automotive finishes work well on exterior wood, but the manufacturers reportedly won't stand behind it. March 12, 2006

Has anybody tried automotive clearcoat on an exterior door?

Forum Responses
(Finishing Forum)
From contributor H:
Automotive is a great exterior solution. I do it all the time.

From contributor D:
ML Campbell has a new line of 2k exterior grade coatings. And since you are doing wood/millwork, tech support is as close as your nearest supplier. Explore this new line first.

From the original questioner:
I forgot to mention that I plan on using Deft lacquer sanding sealer to seal the door first. Would this present any problems? I've done a sample board and it looks pretty good.

From contributor B:
Not on an exterior door! Stay with the same system throughout. If you're going to use automotive clear coats, stay with the recommended sealers for the topcoat. I don't care how good it looks on the sample - it's what lasts on the exterior door.

From contributor A:
We've used Imron clear on teak toe rails on our racing boat for 10 years. It's bombproof. The one downside is it has no UV inhibitors, so depending on what your door material is, this could present a problem.

The other product to consider is Awl Brite. It's made by the Awl Grip manufacturer. It's a 2 or 3 component system with tons of UV. Jamestown Distributors is a good source.

From contributor S:
Under no circumstances should you put a crap lacquer like Deft under automotive acrylic urethane clear coat. For one, it's not compatible and two, it's completely unnecessary. I've shot a ton of exterior doors with automotive clear coat. Here's the hot setup:

Coat one.
Mix up the clearcoat according to manufacturer's recommendations. Normally 2:1 or 4:1 clearcoat and activator. Reduce this 50% with the appropriate temperature urethane grade reducer. Let dry and sand away the raised grain. I like a sanding sponge for this purpose.

Subsequent coats.
Mix up normally and reduce 10-15% with the appropriate temperature urethane grade reducer. Only drawback is that it comes in one gloss (mega shiny).

From contributor J:
I have used Mathews for quite some time. This is bulletproof. It is a 3:1:1 mixture. Use it for commercial bar rails all the time. Easy to spray and flows out great.

Mathews = Mathews Paint Company, MPC. The shop next to mine does fiberglass repair for Busch Gardens, Sea World and the like. Most of the repairs are MPC products. All products are a 2k. The product that I have used is a 3:1:1, including the paint. Not cheap by any means, but worth the cost, about 140 per kit. Clear, reducer, catalyst. Sprays like a dream in cold and in hot humid Florida weather, of course with the appropriate reducer. I buy it from local PPG.

From Bob Niemeyer, forum technical advisor:
Last year I did an article for "Finishing" magazine on exterior urethanes. During my research, not one automotive coatings manufacturer would comment on the use of their products on wood.

Exterior 2K urethanes for wood need to have very special properties built into them. The Europeans have been doing this for years and are very good at it. It also comes in sheens, not just high-gloss.

From contributor K:
If you want a lower gloss automotive clear, ask the paint guy where you buy it. Most auto paint suppliers have a flattening agent you can add to tone it down.