Poplar in Exterior Conditions

      Although some people have noted 100-year-old poplar porch posts that are still sound, poplar generally seems to rot quickly in exterior use. November 10, 2005

Question
I have 30 poplar porch posts to make that are 7" round. I am wondering if I should use 1" thick poplar laminated, or 2" or thicker, as this would reduce my glue up time. I am concerned about the movement of the wood. I may glue a box out of thicker material and leaving the middle hollow. This shouldn't interfere with my turning profile.

Forum Responses
(Architectural Woodworking Forum)
From contributor L:
If the posts are at all exposed to the weather, I wouldn't use poplar, which is not at all durable to the weather! For inside work, I'd glue-up 8/4 poplar that is 6-7% moisture content. If the posts are to go outside, the equilibrium moisture content will vary greatly depending on where you are and what season. Things get riskier the bigger the moisture swings. Most old house posts were hollow, reducing the affect of moisture changes.



From contributor G:
I have torn a lot of poplar siding off old houses that was poorly painted and was hard as a brick. If it's near the ground, it will rot.


From contributor D:
Do it and make sure the inside is sealed well.


From the original questioner:
They are going to be used outdoors, but I'm not really concerned about the wood. The porch is already 4' above the ground and I am going to notch the bottom of the posts so they sit on the corners and have possibly some aluminum under that, then cover that with poplar molding. They will be painted.

Contributor D, are you suggesting that I leave the middle hollow and finished inside? Any advantages to poly glues rather than Titebond 2 or 3?



From contributor P:
Sure, use poplar outside. Then you get to do the job again in three years. Or less. I made some poplar column bases as a favor for my neighbor - lasted 3 years, then rotted.


From contributor R:
I used some poplar on my own garage. I made sure to prime all sides. Used the best 100% acrylic exterior paint and within 3 years, the poplar failed. Please, don't use poplar... I would even avoid using it on the interior of a house.


From the original questioner:
What kind of wood do you recommend that is going to be halfway economic? I don't understand the hang up on the poplar. I know of two houses built in the 1880's around here that had poplar porch posts that were replaced just in the last ten years. Has poplar changed or old growth versus new growth? I can't hardly believe that the poplar just rotted away, as I have had poplar heart cuts laying outside with no finish whatsoever for at least 1 1/2 years. They still seem solid. Did any glue joints fail, allowing moisture to penetrate? As I stated, these will not be on the ground and will not sit directly on the porch. I am in Ohio. Does the climate here affect poplar differently than in your areas? I have decided that whatever I do, they will be hollow in the center so as to have some equilibrium on the outside and the inside.


From contributor B:
This is not the first time I have heard this legend about old poplar in the weather. I too know for fact that the poplar (Tulip) of today is the absolute worst for rotting with any exposure. Were the old timers using something else?


From contributor G:
Makes you wish you hadn't ask, doesn't it? There is some difference between old and recent growth. I think finishing it the way they used to is the key. You have to leave the wood some room to breath. New log homes are finished with coatings that allow for this. Build it, paint it on the outside, and see what happens. Don't paint on the inside. Seals in moisture that can't escape and will rot. Cap it on the topside so water can't get to the center. Should be out of direct weather, as under a porch roof.


From contributor S:
I have watched this poplar/exterior thing for 25 years, and I agree that it is perhaps the worst wood to use in exterior situations. That said, here in Indiana (poplar is the state tree), the old poplar in restored and preserved buildings has lasted well over 100 years. The difference is between old growth and current harvesting. The old growth material is heartwood, very dense, with 80-100 rings per inch, and the new stuff is sapwood and 4-8 rings per inch. It is grown like corn, I think.

As to your choices with economy in mind, don't think of economy as initial material cost only. Good materials cost more, but they age well and are an efficient use of resources - wood, capital, your labor, etc. Do not let the customer drive the cost here - the project will call for a certain level of performance, and that is what you should deliver, in my opinion.

We use cypress, Honduras mahogany, and on occasion, Western red cedar for this kind of work. If these are to be 7" square, use 8/4 glued up hollow with West epoxy, then prime the interior, and insure they are installed so the interior vents in height, just like round columns - so air can circulate up and out the top. I think solids would self destruct from expansion/contraction at that size cross section. A metal base (or Teak or Ipe) to raise the foot of the column out of standing water will help also.



From contributor M:
Spanish cedar is a nice, economical replacement choice, also.


From contributor G:
I have some poplar (new growth) on a barn that we never got around to painting. Been there 15 years. Weathered a lot, but still solid. It does get a lot of air flow.


From contributor B:
This is still conflicting info. Here in VA, commercially available "poplar" is mostly tulip tree (Liriodendron tulipefera L.), a member of the Magnolia Family. I have also seen cucumber tree mixed in. Neither is worth spit for enduring the elements. Is there no one out there with some real understanding of this weather proof whitewood? Are we all looking at different birds and calling them a duck? Was there really some magical property in the old growth heartwood that cannot be recreated? I have noticed when working the occasional dark heartwood piece that it really makes a raunchy smell quite unlike regular sapwood.


From contributor S:
I don't see where the problem is. What is commercially available as poplar is, as you say, not worth spit for exterior work. I don't know what you mean when you say "weather proof whitewood" - is that old or new? I would advise steering wide of anything with a questionable use in exterior work, and move toward the species that are not in question. The informed consensus is that the density of old growth poplar heartwood (a vague catch-all term that will have to suffice until someone defines it better) is far more durable than contemporary poplar. It is neither magic or mystery - yet I'm unable to describe the science. My opinion is not based upon hearsay, anecdotes or legend, but close observation over time. I have seen one window company fail spectacularly because they took a leading state university's advice on poplar. The liability claims killed them in 5 years. I have seen two millwork shops nearly die because of a change to poplar (from sugar pine) in the late 70's, and the resulting claims and damaged reputations. I get requests/specs for exterior use of poplar (usually based on hearsay or most often, price), and I carefully try to educate and substitute. There is a big difference in use/utility between unpainted barn siding, and joined millwork, obviously.


From contributor A:
Poplar - both Populus spp. and Liriodendron - is not a naturally durable wood. The various species are all rated as "non resistant." This is the case, regardless of whether it is old growth or new. Poplar species do not form a regular or durable heartwood.

This puts poplar wood at an inherent disadvantage for exterior work, where the risk of wetting - and hence decay - is higher. However, poplar, or any species, can be used successfully outside if it is kept dry. All wood becomes susceptible to attack when wetted. Woods with natural durability such as western red cedar (or even white pine - heartwood in all cases - all sapwood is susceptible) can provide some insurance against rotting when the wood gets wet. As can the application of preservative chemicals. However, proper design that keeps the wood from getting and staying wet is the key to durable performance from any species.

Reports of longevity for poplar ("it's been there for 100 years") reflect good design or fortunate circumstances (i.e. it's not getting wet), rather than some inherent superiority of the wood. All of the old growth poplar that was used 100 years ago that did get wet has long since rotted, so we can't judge its performance.

Painting wood can help the piece shed rain, thus reducing wetting. Painting the back side is recommended because it slows - but does not stop - the movement of water vapour into and out of the wood. However, painting wood will not seal in moisture and make it rot, although it is often tempting to blame the paint.



From contributor J:
If you leave the center hollow, why not set a metal post inside? Adds more support, making the poplar a cosmetic feature. One suggestion: if the posts are going to be painted, coat the bottom portion (or any place where dirt can accumulate) with fiberglass resin, sand it smooth and then paint. I did this 15 years ago with Doug fir, which was sitting exposed to the weather on concrete, and the posts are still sound with no signs of rot.


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

Comment from contributor R:
Let me add my experience to exterior use of poplar. I needed to make small custom door for a back entrance and I used poplar for the stiles and rails and MDF for the flat panel. I made sure that all surfaces were coated with two coats of a vinyl primer and two coats of an exterior latex. It has been three plus years and no sign of rot or movement. I also applied a wax type of lumber seal to the end grain prior to priming. The door has no overhang and a northern exposure in western NY.



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