Exterior door finishes

Products to use for protection from rain. May 22, 2002

I'm doing a solid oak door that will have minimal sunlight exposure with considerable exposure to rain. Any suggestions on what would provide the best protection and wear? Client already knows it won't last forever.

Forum Responses
1st choice - High quality primer followed by paint.
2nd choice - High quality spar varnish.

Whatever you use, be sure and remove all hardware and apply finish to all surfaces, including top, bottom and sides. To keep exterior wood doors looking good and lasting longer, apply a dollop of silicone adhesive into the holes just before applying any fasteners (screws, nails).

From contributor D:
Acrylic urethane would be best. MacLac makes a very nice product of this description. Rudd Prothane is a very good choice if not in full sun continuously.

From the original questioner:
Do you think a vinyl sealer with Magna Lac pre cat lacquer as a topcoat lasts longer than the varnish or acrylic urethane? The color will be natural with a Van Dyke glaze, if it makes a difference.

No, Magnalac is an inside type product.

From contributor M:
With an exterior door unit that gets a high degree of moisture you need to
1) Paint the top and bottom with oil enamel paint.
2) Stain with something with a UTC based stain.
3) Apply SW Homiclad sealer as you would a stain.
4) Finish with a catalyzed urethane such as SW Polane, Pinnical, PPG Flexicron. 4 to 6 coats and do not rub the finish out, as this will destroy the surface protection.

Aliphatic urethane is a 2 part exterior finish, which works great for exterior doors. UV stability, durable and non-yellowing. It comes in 3 sheens - gloss, semi-gloss and satin. There are some Atlanta area shops using this product and having great results. Vinyl sealer and Magnalac both are interior products - they are not meant to hold up in an exterior application.

Lisa Gilbert, forum technical advisor

From contributor D:
Which brand of aliphatic urethane are these people using? My boss has a boat he'd like me to re-finish the woodwork in and this seems like the way to go.

This one is a Gemini product out of El Reno, OK.

Lisa Gilbert, forum technical advisor

Contributor D, the product you want, since it is for your boss and he is going to pay for it, is Sterling Linear Urethane. Apply a base wiping coat of SW Homoclad sealer and spray 4 coats of topcoat. This is the most costly finish I have ever shot but it is the most durable.

I agree with painting the top and bottom edges of the door. I always use a high-quality exterior enamel. Unfortunately, sometimes door installers need to trim the doors to fit and they are not as diligent at repainting what they cut off. I have also had good luck with automotive acrylic lacquer (PPG) at Lake Tahoe (pretty nasty up there in the winter) in protected areas.

From contributor R:
Could one use aliphatic urethane on a red oak exterior door that has a heavy sun exposure? Or will the wood movement be too much for this type of film to handle? I have a client that needs a front door redone that I've been re-varnishing for years. It's finally gotten to the point that it needs to be stripped, re-stained and finished.

From contributor D:
It's the second best choice behind linear polyurethane. The aliphatic urethane Lisa refers to costs as much per gallon as the linear poly costs per quart.

What is linear poly and can it be stripped eventually?

From contributor D:
It's a very high-end clear coating that's commonly used on yachts in place of spar varnish. Damn near bomb-proof according to the people I've talked with that have used it. It strips great with a belt sander.

From contributor M:

Linear strips very nicely as long as you get under it. It is not like stripping old polyester. The trick with any exterior finish is not to get to the point of having to strip the material off. Before the finish crazes, powders or loses its color, you want to re-coat the item. This goes for anything from your offshore cabin cruiser to my front door. Most exterior finishes have UV absorbers that get used up and must be renewed or the finish, stain and wood will be destroyed. When customers call us with a door re-coat, we get out there now. When they need a door refinished, I normally do not return the phone call.

From contributor D:
It still WOULD strip nicely with a belt sander, wouldn't it? I never said it wouldn't strip with MC stripper. Actually, I thought from the descriptions of linear poly that I read on some of the boating sites, where this stuff is popular, that the stuff was like polyester. For polyester I'd recommend a blowtorch or the aforementioned atomic bomb. The brand of linear poly mentioned a lot on these boating sites was some stuff I believe was called Awl-Grip? Is the Sterling product similar?

From contributor R:
My biggest concern here is UV exposure and longevity. Unfortunately, the door in question gets sun from the lock rail down for the better part of the day. Plain cut red oak, a dark stain color and south exposure (dew at night) aren't helping matters, either. Could any of these finishes hold up for say five years, maintenance free? I'd hate to go to the expense and be back where I started a year from now.

From contributor O:
Your best bet if you have the money to spend is Sterling two-part linear polyurethane. At $240 a gallon + $240 for the catalyst it'll be an expensive door finish.

Contributor M, have you ever worked with marine finishing products? They are not the same as painting or glazing a wood door.

From contributor M:
Yes, I have done some work with marine finishing products, also exotic car interiors and very expensive exterior entrance units. As far as I know, there is no magic to the chemistry of the products used in the marine industry. The wood that is used is the same and so are the environmental extremes. Moisture resistance, UV exposure and chemical resistance concerns are all the same. As a company that finishes and refinishes a wide range of products and surfaces, it is our profession to find out new or different products from a wide range of fields. So please let me know what you have hiding in your bag of tricks.

From contributor O:
I don't have anything hiding, only experience in building 40-60 footer sail yachts. And yes, there are some tricks by working with polyesters, vinylesters, polyurethanes, epoxies, etc. If you mix a gallon of primer with the catalyst from brand "A" and start shooting you have wasted 500 bucks.

Having done some work with marine finishing products is not the same as working in a marine environment. The wood used in a marine environment is not the same as the one used in kitchen cabinets and the finish is also not the same. Marine products have their use "on the water". For on land use, they are too expensive.