Locust for Window Sashes?

Locust is durable and rot-resistant, but it's not stable or easy to machine ó so probably not the best choice for window parts. January 23, 2014

(WOODWEB Member):
I have a large number of locust posts (black locust I believe as they have thick creviced bark) that I would like to use for casement window sashes. The posts are about 3 inches in diameter or larger sizes that have been split in half or quartered. The posts have been stored dry in my parentís barn in upstate NY for about 40 years.

I have read several woodworking forums that recommend staying away from locust for sashes as it can warp, crack, and check. Is that the case only for newly felled timber, or for long dried wood as well? A local lumberyard owner told me he cannot get locust that is kiln dried, and recommended Philippine mahogany which he said was cheaper than locust. I want to use the locust because: I donít want it to go to waste, itís free, and above all it is so resistant to rot Ė posts I put in swampy areas as a boy are still standing while the barbed wire is sagging or down. However, I donít want to make 27 sashes and find them warped and cracked in a few years. If not locust, what about white oak Ė the sills and frames are made of white oak. Thanks in advance.

Forum Responses
(Architectural Woodworking Forum)
From Professor Gene Wengert, forum technical advisor:
It is difficult to use any species of wood, have it get rained on and then have the sun dry it, without getting checks, cracks, warp and oftentimes decay. You have two options.

1. Use a coating that will repel water and use construction techniques that will not trap water and will allow for drying.
2. Use a preservative treated piece of wood to avoid decay, but not all the other issues.

Locust is difficult to mill, with rapid dulling. It does have natural decay resistance that is pretty good - heartwood only. But warp and checks are likely when cycled between wet and dry. Locust is also heavy. Basically, I believe it is not the proper choice for this use.

From contributor M:

I don't know how many locust posts you've split in your time but on my farm I have split a lot and the locals around me have split tens of thousands. With that I have never seen any/many that are clean/clear/straight grained/etc., especially when they are split from a single small stem into 4-6 posts. It is even rare to find a large locust that is reasonably straight and sound, forget about the smaller stems normally cut for posts.

I would have a hard time seeing how any amount of cost savings from these posts being free would add up after you figure out a way to mill these short split pieces into lumber and then kiln dry them. The work in that alone would be very substantial to say the least and I can only guess the resulting material may be questionable at best.

It's definitely tough stuff, hard on tooling, and can be pretty, but I'd be concerned about putting all the work into building sash from fence posts. It would seem you may be better served to scour the property for a few nice larger locusts and have a local band mill saw them up and then dry the resulting lumber.

From contributor L:
I'll wager you will regret trying to use that stuff. The cracks will be full of dirt and quickly trash your tooling. You also need to meter it. Just because it's laid around the barn a long time doesn't mean it's at the ideal moisture content.

From the original questioner:
Thanks for your input. I will not be using the locust posts for sashes. If I understand correctly locust is not necessarily more prone to warping and checking, but it will be difficult to find enough clear wood, difficult to tool and quickly dull my blades. Reading another recent post here about Accoya (proprietary name), Iíll look into that or fall back on Philippine mahogany. Whatever I choose, Iíll make sure to waterproof it. Three coats of marine spar varnish is what I usually use.

Are there any uses for locust other than fence posts?

From contributor L:
We've run some locally milled honey locust into moldings for other people and used a little of it in personal projects. It ran fine and for what I used it for it seemed okay, but I don't have a lot of experience with it.

From the original questioner:
I think I'll cut some up and see how it works.

From contributor J:
Locust heartwood is very rot resistant. We buy dowels from Germany (from Spilker) for doors and windows made from locust. They call it Robinien. The building codes over there do not allow beech or birch dowels for exterior work because those species rot quickly. Like everyone says, I don't think it is good for anything large, but might work for something like dowels.

I had not looked at the Spilker website for a while. Looks like they offer more locust products now.

From contributor Z:
During the wooden ship era, locust was the primary wood for the pegs that held them together.

From the original questioner:
Although Iíve taken some sashes apart and found the dowels in pretty bad shape, I didnít realize the type of dowels in window construction was so important. Iíll have a German friend navigate through the site to order some.

Thatís an interesting fact about ship building. I suppose it says a lot about the practical uses of different wood.

From contributor C:
From my limited experience, black locust tends to split, warp and crack during the drying process. That is one of the reasons you never see large planks of it. It also has a waxy oil in it that makes it hard to sand. My guess is that is why it was good for shipbuilding and fence post, in that these oils made them rot resistant.

From the original questioner:
That was part of my original question Ė if the wood has dried protected in a barn for 40 years, has it finished warping and cracking and is any straight lumber I cut going to remain straight, or will it continue to warp and check once itís milled? So far from what Iíve read, I donít think Iíll be using these posts for any serious structural work.

From contributor M:
What you have to remember is the locust that has sat in that barn is not at its final moisture content even for exterior window sash. I would venture to guess the material is in the 20%+ MC range unless it's in a hot attic, and typically any material you would purchase commercially to build sash will be well below 10% MC.

The material can most definitely be used for something if you choose to go through the work of milling it into boards, but as a general rule when one goes through the painstaking process of building window sash, you try to start from as solid a footing as possible. The material may in fact be suitable for the sash if you have enough time and are up for the task, but if you apply even a trivial amount to your time and machinery ($5/hour), it will likely turn out to be some very expensive wood.

Locust is commercially available from many sources and a google of black locust or locust and then to images will take you on a tour.

From the original questioner:
I was quickly disabused of using the locust for sashes after the first few posts, although I will mill and turn some just to see what it looks like.

Your info on moisture content is what interests me. If commercial kiln dried has ~10% MC, how long does it stay that way? Wouldnít it eventually increase to ~20%? If so, would it be better to let the wood acclimate to 20% before making sashes so that it would be less likely to bind? Also, does kiln drying lumber have an inherent advantage over lumber that is left to sit for long periods? For example, does rapidly removing moisture improve the final quality of the lumber by making it less likely to warp or check?

From contributor D:
Get Bruce Hoadley's "Understanding Wood" to answer all your questions, and more. You'll not regret it. There may also be specific info on the Forest Products Laboratory site - Dr. Gene's home stomping ground.

From the original questioner:
Thanks for these references, Iíve already bought "Understanding Wood" online. Do you know of any equally good books on sash construction?

From contributor A:
Check out the forums at Historic Homeworks. They're a bunch of people who make vintage sashes the old fashioned way. You'll learn lots like how to relish and haunch your joints. Some fun! Also check out AWWM. Tons of info on the belt driven machinery used in the 19th c. Okay, AWWM is not practical for you, but it's awesome nonetheless.