Exterior Wood Finish Maintenance

This long discussion starts with a question about maintaining the finish on a beautiful outdoor wood gate, and continues into a detailed examination of the difficult durability issues with exterior clear finishes. January 14, 2008

A year ago I did this custom job for a client. It was an exterior gate in a wood finish. It is finished with D-Dur exterior 2K urethane. I was very nervous about actually doing this project, as no one has much good to say about the long term prospects for these types of exterior finishes in a northeastern climate. However, I did it anyway and offered the customer an annual maintenance package so that I could care for the gate and not have it degrade quickly and cause any bad publicity for myself.

My plan is to wash and wax this peace each fall. Any recommendations for a wax that would be suited for this type of project? Do you agree with my plan?

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Forum Responses
(Finishing Forum)
From contributor D:
I hope your maintenance contract is open ended. You never see work like this for a reason. It simply will not last. Even if the construction and materials are very robust, the finish deteriorates so quickly and with so little regard for your skills that all parties eventually tire of it and start the paint cycle.

I see flats (horizontal surfaces) all over this assembly - never a good thing when there is any rain. Water will sit on top of anything less than a 7 degree angle. It will find its way under the finish. It is not the finish's problem - it is the nature of the beast. I personally hate to say it, with the obvious amount of work and expense, but your work is doomed.

As for your question, wash and wax each Fall is fine, though moot in the larger context.

From contributor A:
That is the nicest gate I've seen on a modern house. Excellent craftsmanship. How many coats of 2k did you apply? What kind of money is your maintenance contract worth? I would think if you managed to get enough film thickness, it might have a chance. Otherwise the water will find its way into every nook and cranny. What wood did you use?

From the original questioner:
Thanks. None of the surfaces are flat. The top rails are tapered. The posts are finished with pyramids. Already considered that settling water would be an issue.

None of the wood touches the ground. The fence has a hidden steel substructure and is floating on the steel reversed angle iron frame routed out of in the rails and posts, with steel rod running crossways to keep the 2 x 2's from twisting. The posts are sleeved over 3" 1/4" steel tubing and bolted on for stability and to keep the post off the ground.

The urethane is four brushed coats. It is very thick. The wood is pine. The maintenance package is a fair price for my time. And yes, it will get painted one day. But not today.

Any recommendations on a good product to keep it good as long as I can? Someone mentioned in one article to treat exterior wood finishes like a car. Hence wax.

From contributor W:
Well, I think it's going to last longer than anyone thinks... It's an exterior poly. The one thing to be concerned about is how much UV protection or additive was in the product. The color will be the first to go, I would think.

From contributor R:
Nice gate! It sounds like you did your homework. I hope you sealed all of the unexposed end grain really well. I like West System epoxy myself. I have used D-Dur on a couple of jobs at Lake Tahoe and they have held up well. The color may well fade and I don't think pine was a very good exterior choice. Doug fir would have been better, or for a gate that nice, mahogany would have been beautiful. The wax will help with moisture, but UV is the big problem and it looks like your gate is sitting out in the open sun. I would think after a couple years it will need to be re-coated. I would carefully wash off all the wax and then apply a tinted coat of D-Dur to restore the color and use a pigment - not a dye - as you will get better UV protection. Let us know how it holds up. I always like to check on my projects over time to see where improvements can be made.

From the original questioner:
Thanks again for the feedback. I had not heard that mahogany was an exterior wood choice, and if it was, the customer would have paid a small fortune, so cost would be an issue. Fir I just never warmed up to myself. What is wrong with pine? Does it not have at least have some anti-fungal properties?

Anyway, the nice thing about this piece is the entire thing comes off the frame in under two hours and can be off to the shop.

Back to my original question, though. Nothing of a special note on the wax - just something good and hard. Would you use furniture wax or car wax, for example?

From contributor O:
Beautiful work both in construction and finishing. Sounds as if you did your homework. I might suggest an automotive wax. If the wax is used on a car that sits out in the elements, it should be good for a gate that sits outside too. I'm just guessing on the wax, but for sure mahogany is a great exterior wood - just look at all the boats that have mahogany rails and doors, etc.

How does the gate look a year later?

From the original questioner:
I was in that neighborhood in July doing another quote. It looked very good. No noticeable fading and I did not see any signs of the finish degrading or blistering. I did not look at it thoroughly, I was just passing by. It looked great.

I think in looking after it annually, I could hope to have it last 7 or 8 years before it needs major attention. One thing about this type of work is that it leads to more requests for more of the same. Not having the benefit of time to prove out my methods is concerning. Hence important to ask the questions of others who do have some experience in these finish applications. Most of the methods I did use were from advice I received in this site, which I am very grateful to have available as a resource.

From contributor L:
Types of wood you can use in lieu of pine would be mahogany, cypress, cedar, and teak. I'm sure there are some other good wood species from South America as well. Auto wax should be the product for outside.

From contributor A:
What woods have anti-fungal properties other than pressure treated? Old growth eastern white pine would be suitable, however it is not available. New growth will rot pretty quick. Most pine is ponderosa and is not rated for exterior, only interior, millwork. That is why so many modern wood sashes end up dissolving after 10 years. The other concern is the stain. I've never heard of a good experience with exterior stains.

I don't understand the "yes it will get painted one day, but not today" comment. Why not paint it today and forget about it?

From contributor Q:

Nice gate. I do a lot of exterior doors in NJ. The factor that will decide the life of finish is how many hours of direct sun it gets. Any more than four and D-Dur will start to lift from the wood next year, so the big problem becomes putting on another coat. If you just scuff and reapply, it will help, but the original finish has really started its delamination process. Wax won't really add any life to the finish; it will just spruce it up. When you sell a maintenance package, the customer is inclined to think this is all that's needed. You have to paint (no pun intended) a doom and gloom outlook to customer about clear exterior finishes. One thing I have tested is taking SPF 50 sunscreen and adding powder aniline dye to it and putting it on the finish. Doesn't work great on large flat panels, but on your gate it should help. You will have to strip finish completely off at one point (fun); if you got five years, that would be great. I did two mahogany doors on the same street, one on one side, one on the other. The first one that I did six years ago gets very little sun and still looks great. Across the street, I refinished not even three years ago; it gets lots of sun, and I am refinishing it again next month. Both have the same finish.

From contributor P:
A potential problem with auto wax - some of them contain silicone, which could make your life miserable if you ever have to bring the piece back to your shop to refinish. The stuff will contaminate your shop and cause fisheyes, even possibly on other projects.

From contributor J:
Pine is great as an exterior wood! A very large and expensive millwork shop in Washington, DC uses ponderosa pine for many exterior door window and millwork applications. Also Pella, Marvin, and Anderson use pine extensively in their products. I think exterior millwork is all they do. Yes, I know that they all offer an exterior cladding as an option.

From the original questioner:
In regards to the pine as choice of wood, I was confused about that. Are board and batten structures not pine left raw to the elements in many instances? The notion that pine was a poor choice did not jive with my research. Would an option have been to use one of those log cabin stains that boast trans-oxides for UV resistance, then top coat with an oil product for sheen? Would this allow you to just keep re-staining as required and oiling annually? I think this type of top coating care would be similar to the care required on EPA decking due to the wood's density.

From contributor W:
I think I would look into that option... Pine here in the south has always been used for outside work, although many years ago it was heart pine, while it was so abundant and cheap. But Sikkens makes a very good outside product... both stain and topcoat. Understand that topcoats have two functions... one that penetrates the wood and the other which lies on top. The latter is the one that deteriorates so fast by UV and moisture getting under the coating. So it's a matter of looks as to which one you want to use. If you use the penetrating coating, then an application of wax on that will elongate the finish if you have some/good UV protection in that and in the stain. My opinion, anyway.

From contributor O:
I'm wondering why no one has mentioned an automotive coating for an application such as this. You can't get much better when it comes to UV protection than auto coatings. They are flexible, which would allow for expansion and contraction, and the clarity of the coating is rather apparent. You also have aisles upon aisles of various waxes that are formulated for these types of coatings. Given all these advantages, it could be just what the doctor ordered.

From contributor D:
Automotive coatings do not work in exterior environments due to the wood movement. They will only work in interior environments on stable, board type items.

The reason many thick (or even more thin) coats is not a better strategy is that the coatings separate from the wood, and then moisture creeps in. All wood coatings have to remain flexible, and exterior coatings even more so, due not only to wood movement, but also temperature changes affecting the elasticity. Choose whatever make or type you want (Enduro, Foreva, IronClad, BeastMaster, Longlasta, SuproGloss). If it gets too thick, or when it ages, it loses its elasticity and then fails. Period.

Wax is a thin, active barrier that will have little effect on things as exposed as the gate in question. At the extreme is the SPF 50 lotion - enough said.

As for species: If finish is desired, then Honduras mahogany will be the best bet, in my opinion, and forget the stain. Forget the expense. The project is larger than the expense. White pine is a pretty good exterior wood. I prefer sugar pine over ponderosa. I see the "builder line" of pine windows repeatedly failing after 8-10 years, but that has more to do with poor glass seals and weatherstripping than the wood itself. If there will be no finish, then teak, with real joinery and such. That will affect the design greatly, since Victoriana would never compromise for joinery - it is all about decorating the decoration.

There are two ways to deal with exterior wood: Do nothing or start a finish cycle. Cycle as in repetitive, for life, where sooner or later someone neglects or fails or just plain moves on, and will no longer devote the time previously spent on maintenance. Cycle as in fight the nature of the material and the environment actively, for life.

Do nothing, as in teak or ipe or others where the material has the natural durability to age without rotting or splintering, and will blend with the environment in a slow natural manner that respects the wood for what it is. Witness the teak garden furniture that is over 100 years old.

Plenty of people with far more at risk than us have tried for many years to come up with a better finish for exterior (although I admit the SPF has got to be a new one). It won't happen. It is all about the nature of the application, not the desire of manufacturers or the consumer.

Sadly, there will be nothing new to this particular or general discussion. There is a reason why one doesn't see this type of work often. When it is seen, it is for only a while until nature, in one form or the other, will take over.

From contributor P:
Another thought on the automotive paint issue... Years back when I painted a few cars, automotive finishes had an additive that the finisher would add when spraying flexible body parts (rubber bumpers, fender flares, etc.). I wonder if this would solve (or at least improve on) the wood movement issue.

From contributor R:
I don't think most automotive waxes would be good because they turn white when they dry, that's why we use a clear paste wax on wood usually. The only protection a wax would give would be from moisture. I have used many automotive finishes on exterior doors over the years and the only successful attempts were on doors in a protective porch situation. The very best exterior finish I have tried so far is the Sikkens Cetol system. It does fade in direct sun situations, but a fresh coat of the colored Cetol 23 solves the problem and you do not need to strip and re-finish. I brush on the Cetol 1, which is required, and then I spray on the two coats of Cetol 23. Makes a nice finish. I also have had good success with the Epifanes line of coatings which are for use on yachts. They have excellent prep instructions on their web site. I love their PP varnish.

From contributor J:
Thanks for the good tip on Sikkens. I called a dealer in Reno and they recommended their log and siding product as a reformulated/improved single step system. The salesman said I would have no loss of durability versus Sikkens 1 and 23. I would like your opinion as you have real world experience.

From the original questioner:
When originally approaching this project, I considered finishing it like a wood boat. I have a friend in the industry and we discussed epoxy finishes with a clear coat for UV. But it seemed that blistering was going to remain an issue. So I passed.

I called Chemcraft and the tech guy I spoke to was very enthusiastic about the properties of D-Dur and that it was formulated to allow vapours through the finish if applied properly, while maintaining a good moisture barrier. I had other contacts locally that had used it and gave the product a good review. At some point you have to decide and just do it.

I touched up this project yesterday, and the results were far better than expected. Due to the direction of the house and a few sizeable trees in front, I could not identify any noticeable fading. None that was obvious, and only two minor areas where the finish had clearly collected some water. But overall, it looked as good as the photo above. So I suppose the environment will play in my favor this time. I think I will quit while I'm ahead, though, and seriously consider ever doing another.

From contributor R:
I have heard of this new product from Sikkens but have not used it myself, so I really can't recommend it. I really like the Cetol product. We used it on a set of "doors from Hell" project. Direct sun most of the day, absolutely no protection (and of course the project manager failed to mention any of these facts!).

Automotive finish bubbled and blistered off like crazy from the intense heat. We refinished using the Sikkens Cetol system and after a year of sun and cold and snow, the only problem was a little fading which was taken care of with a fresh coat of the Cetol 23.

From contributor E:
Listen to contributor R - he knows his stuff. With respect to newer automotive coatings, most modern clear coats no longer require what was at one time called a flex additive. This came about when urethane bumper covers became popular. The automotive coatings manufacturers needed to improve the flexibility of their clears to deal with the extreme flexibility of these bumper covers. So no more flex additives are needed.

Since pine is a fairly mundane wood grain-wise without much feature, why not construct such a project out of Extira MDF? This stuff is almost completely waterproof and can be stained pretty much like pine. If you were using something with a ton a grain like oak, that would be different, but brown stained pine doesn't look that different to me from toned MDF.

From contributor C:
I don't see why an automotive clear polyurethane wouldn't work best. After all, it's used on boats and airplanes. As far as flexibility, it holds up on car bumpers, so surely it will be flexible enough for wood.

From contributor S:
The problem with clears on exterior timber is the damage that light does to the surface of the timber. Both UV and visible light will do damage, so you need both UV filters and some colour in the system. You will see this in products like Sikkens. Even their so-called "natural" finishes contain a small amount of colour to boost the performance.

Which pine doesn't have much feature? Most temperate softwoods show a good variation between early and late wood. Tropical species often have little variation, as they grow at the same rate all year round.

From contributor C:
Automotive clear has UV inhibitors. It's a very important component to protect the basecoat paint. Without it, most colors fade quickly. Whether it's enough on wood...?

From contributor S:
Auto clear will do better than standard varnish, but as it contains no colour, it cannot protect against damage to the timber by visible light. I often see clear finishes being returned for analysis. The dry film is sound and very flexible, but the reverse face is covered in delignified timber fibres which have been damaged by visible light. The coating peels off in sheets.

From contributor C:
This is an interesting issue that I've been trying to get an answer on in the past. A lot of car people have used clear on wood on cars and I've wondered if it would hold up to the weather. What about furniture indoors? It gets plenty of light.

From contributor S:
The energy levels that cause the damage, both in UV and visible, are reduced when passing through window glass. The energy level is then just enough to cause a bit of bleaching, but not enough to degrade the lignin in the timber. Once the lignin is broken down to sugars, there is a need for moisture to wash out the sugars to complete the degradation. This is why clears appear to do well in areas of high sunlight and low rainfall (and vice versa). Anyone who owns a boat will tell you what a pain clear varnish is, no matter what the formulation.

From contributor A:
Most people's experience with varnish goes something like this. It looked perfect until it got dinged or scratched. Water finds its way behind the film the wood oxidizes and the film starts to fail and eventually peel off. Three years later, wherever the damage occurred, the finish needs to be brought back to bare wood. The finish looks great everywhere else. We used Imron clear coat on teak toe rails on our race boat for years. It would take a lot of abuse and almost never scratch.

Regular varnish would have to be wooded every year in that application. The wood moves thing seems a little blown out of proportion in my experience. Awlgrip sells a 3 part varnish system if you want to stay away from the typical auto/marine clears.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor A:
I hate to say this but any kind of finish applied to wood will lead, sooner or later to the demise of the wood. Whatever you use, be it paint or clear finish it will not move like the wood to which it is applied. This leads to cracking of the surface which allows water to penetrate and micro-organisms which feed on wood fiber in the presence of water have their way.

I'm afraid that with a finish you describe, white pine is one of the worst woods you could have chosen. Woods high in silicates are the best because they naturally inhibit the growth of those microscopic critters. If you strip the finish off this gate I would highly recommend treating it with a borate solution before finishing again.

Comment from contributor B:
The paint I put on my house blistered off on the side with the sun. When it blistered, it took off more than three layers of paint and the separation point was between the wood and the first layer of paint. This wasn't the UV rays of the sun destroying the top layer of pigmented paint. The paint was blistered by losing its bond to the wood, probably because the sun, in heating the surface (and the underlying wood), released moisture and resins held in the wood. he moisture then lifted the paint.

Automotive paint needs only to adhere to metal and resist the UV rays of the sun. Those of us old enough to remember, sadly, what usually became of those beautiful red cars will remember UV damage as a chalky surface to the finish. Wax helped as it was a sacrificial surface periodically replaced.

A wood product left in the elements suffers a symphony of distresses that a car never feels. As long as a car finish will stand up manfully to the sun, remain flexible and not divorce itself from its metal substrate, itís golden. A finish applied over wood, whether it works well on metal or not, is like a frock applied to the devil. The mischievous heart of the wood wins in the end. Woods like teak and mahogany withstand the onslaught of the sun by losing a little of their surface to the elements annually. The reason we laud them is, due to their ability to withstand rot, we can leave them without a surface finish to degrade and peel.

Water doesnít have to seep into the wood to pry off the finish, water is already in there. And, as one poster pointed out, the sun doesnít have to destroy the finish to upend things. The sun need only destroy what wood fibers it can see and the finish will give up its hold and die. Put a clear finish over a piece of wood and the same finish over a piece of plastic and leave them both in the weather. The wood will toss away its finish while the plastic lies mutely through the weather. The plastic is dead while the wood is a living thing, huffing and puffing through its pores with every change in the weather.

But why berate the builder of that incredibly beautiful gate? I once planed all the cedar I used on a deck and then finished the whole thing with spar varnish. It was a hopeless venture but for one season I was able to enjoy the innate beauty of the wood. It was worth it (though the weathering abilities of cedar are overrated).

To have built that gate from imitation wood for the sake of beating the elements temporarily would have been a sacrilege to the muse of woodworking not to mention an affront to the very reasons we work in wood. If you want your labor to stand the ages, build with plastic and fare-thee-well.

If that were my gate Iíd rebuild the house to match the high standards set by the gate.

Comment from contributor C:
No one here seems to understand why clear finishes wonít work well on wood in the outdoors. UV light goes right through the finish and attacks the wood beneath (the pigment in paint would reflect these rays) thus the wood itself begins to deteriorate. The finish can't hold on and move with the degraded surface and is eventually breached. When that happens, water gets underneath and accelerates the breakdown. Multiple coats of spar varnishes with tung oil can stretch some and survive longer, but all of these finishes are pretty much doomed from the outset.

The Sikkens Cetol products have been around for a long time. The way they address the problem is by adding very fine pigment made with iron oxide. The pigment manages to reflect UV rays quite effectively while allowing the wood grain to show through. These are not clear finishes at all, merely "translucent". What's more, the iron oxide adds an unpleasant rust tint to the wood. I've found that it can be difficult to detect how bad this looks with just a small sample. Something can look fine at dawn and dusk, but when the sun shines on it, it can look terrible.

Comment from contributor D:
I obtained my front door from a salvage place. Solid douglas fir and it takes four hours a day of direct sun. I stained it with pigment stain and brushed on eight coats of Minwax spar. That was four years ago. I will need to refinish this year as the color is just starting to fade and the varnish is starting to lift. This is a longer service cycle than I expected. Iím planning to strip to bare wood and go with Epifanes. It probably won't last much longer than the Minwax.

Comment from contributor E:
When playing with exterior finishes and considering urethane, do a bit of research into long and short oil products. Exterior, oil based finishes are among the long oil finish products. This simply means they have more oil, which causes them to be less hard than other finishes but have more flex.

Most oil based finishes use boiled linseed oil. The high end ones use tung oil. In both instances they are polymerized and resins are added to them. As noted by others, more may not always be better. Thicker surface coats may tend to crack more.

I like to treat the wood by getting my protective coating to penetrate as much as possible, before I ever apply a surface coat. This, often, requires staying with the project and keeping it wet for long periods, so the surface doesn't harden and inhibit applying more penetrating protection.

On wax, a review of ingredients will likely show the better products contain carnuba. It is said to be one of, if not the hardest wax. However, it might be you need something that can fill small cracks and such. As such, a mix of hardening carnuba with a non-hardening wax might suit your needs better. The matter deserves more looking into.

In the end and as others noted, ultraviolet will be one of your biggest battles. As such, consideration for ease of future applications of finish is a concern. Avoiding waxes and things that require a team of experts and laborers to remove is good planning. The research into these matters will be well worth it, since you can carry it to other jobs.