The ideal wood to use for outside projects is a question we are often asked in our shop. Any wood exposed to the elements will eventually end-check (split) and begin to fail. Sun is the worst culprit, added to the constant wet/dry exterior cycle. Wood is constantly changing moisture content, which is why it is constantly expanding and contracting. Although all wood will deteriorate with time, some will rot quicker than others, especially here in the Northeast where we live and work.
Fortunately, there are some species available that are extending the lifespan of outdoor projects. The first approach is the use of tropical woods (already I hear the boos and hisses through my internet connection). There are several things wrong with using tropical wood, mainly putting money in the pockets of corrupt warlords and clear cutting rain forests. The physical weight, oil content, and working characteristics of tropical species is hard on tools and those using the tools. That said, tropical species do build into a premium and durable finished product.
Another choice that has become available to us is thermally modified DOMESTIC wood product, in both hardwood and softwood species. In this process, already kiln dried wood is put into a thermal kiln and through exposure to steam and high heat is modified to minimize the lignin and starches, which is food for both macro and micro organisms. These organisms are responsible for your squishy porch railing or picnic table. With nothing to eat, there are no organisms to destroy the integrity of the wood and lifespan lengthens.
We have produced enough professional jobs in the shop from “roasted” wood to confirm that this product and process is here to stay and has more merits than drawbacks, although it has some of those as well.
What’s wrong with it you say? It is expensive, but not prohibitive given it’s attributes. The thermal heating process tends to soften the wood, making it unsuitable for structural (read framing) use and it dents a bit easier.
The best part is that the wood is modified using only heat and steam…no chemicals. Better for the environment, the people producing the millwork, and the end user, which I consider a win/win situation.
For exterior, decorative millwork, thermally modified wood is great. Because the product doesn’t readily absorb water, it must be primed with oil base primer. This generally isn’t a big deal given that all premium grade millwork is primed all faces with oil base primer anyway before paint.
Another terrific attribute of thermally modified wood is that it is, relatively speaking, locally grown. The wood we are building with in the northeast should be grown in the northeast. Keeping the money here can only help our economy. I really like that part.
Learn more about Thermally modified wood here!
Until next time,
Bill Poandl has a BFA in Furniture Design and has been a woodworker all his life