DON'T buy air dried slabs

October 22, 2020

When you check Facebook marketplace, craigslist or other marketplaces, it is easy to find live edge slab lumber. However, a vast majority of the time the slab lumber is “green” or undried, and this is not good.

What is the basic idea of kiln drying? I’ll use an analogy to explain. Kiln drying lumber is the same premise as toasting a piece of bread. You start off with one product, add heat and end up with another product.

Air drying lumber is like putting a piece of bread on your counter for several months. The bread will dry out a bit compared to what it was when it was fresh, but it will never become toast. Toast is bread, but with heat added. The heat cooks the bread, reduces the moisture content of the bread below what was possible with just leaving the toast on the counter and changes the properties of the initial piece of bread. Once that piece of toast is cooked, its pretty hard and doesn’t accept moisture as easily because it’s been cooked. See the difference?

If kiln drying is better why are most slabs not kiln dried? Two main reasons.

#1 – Kilns are a substantial investment and are expensive to run. Kiln operation is also a bit of an art and isn’t something you just “do.” If you don’t run your kiln properly, the pieces of lumber you spent months or years waiting to be a finished product could be ruined.

#2 – The overall drying time for thick slab lumber (think two or three inches thick), from the day of sawing until the day they are down to below 8% moisture content can be a year plus with traditional dehumidification kilns. That is a long time to keep lumber on hand and requires a large area to store all the live edge slabs while they air dry, waiting their turn for the kiln.

What is the downside of using green, non-kiln dried wood in your indoor furniture? Two BIG issues:

#1 – Wood is an organic product, and it moves with the seasons. The bigger the piece of wood (picture a 40 inch wide by eight foot long live edge slab table top), the more potential it has to move. Why do you care if your table moves? Imagine putting a full glass of hot tea on your tabletop and it spills because your top is no longer flat. Can you picture eating from a plate that constantly wobbles because your tabletop is so badly cupped? It takes a long time to get a large piece of slab lumber flat. Even if you flatten a piece of green, non-kiln dried lumber, it will move when the seasons change and the moisture in the air increases or decreases. This will magnify in winter when the moisture content drops, and your lumber is heated by your house and it dries out further. As the slab continues to dry, the lumber will move.

When you air dry lumber (no heat added), the lumber will only obtain the moisture content of the surrounding air. In the New England area, that is around 12-13%. During winter, the air dries out and we heat our houses, causing the air in our houses to dry even further. This will slowly dry that lumber and can wreak havoc on your slab surface.

If you built your furniture, this means you spent hours (and hours) flattening, sanding and finishing your tabletop just to have it move and no longer be flat. If you purchased your live edge slab furniture, this means that you spend (most likely) a good amount of money of a piece of furniture that now doesn’t function very well.

#2 – Bugs! That’s right, bugs…on the wood…in your house. The USDA recommends that lumber be heated above 135 degrees at its core for a minimal amount of time to kill any bugs inside. This means that the kiln temperature must be above that to reach an internal temp of 135 degrees.

So how can we help you with your live edge slab project?

Maine Urban Timber Company sources their slabs from trees removed from urban and residential environments. We cut the trees into slab lumber and then dry them in our vacuum kiln. Our specialty vacuum kiln allows us to dry thick slab lumber in weeks rather than months and gets to temperatures high enough to kill all bugs that once called the lumber home.

Maine Urban Timber Company specializes in Maine hardwood live edge slabs that have been kiln dried to below 8% moisture content. We also keep track of where in Maine our live edge slabs come from so when you buy a slab from us you’ll know where that tree once stood. We also carry hardwood slab lumber from Maine trees that aren’t commercially available.

Are you working on a live edge table, need live edge shelves or want to install live edge slab countertops? Maine Urban Timber Company has what you need. Get in touch with us to see what we have and what you need for your next hardwood live edge slab project.