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Moisture Content Of Wood
What is the right moisture content in wood for making furniture?
I have a 14 foot X 28 foot shop in which I only run the AC or Heater when I'm using it for woodworking. Thing is, I wish to use hardwoods to make furniture. So what can I do to keep my lumber moisture content right so that it is workable?
Help!!!
We often get the question - how dry should wood be for woodworking? Kiln dried lumber lumber should read as having moisture content from around 8% - 12% which is a standard moisture content for furniture grade, kiln dried lumber. Typically, kiln dried hardwood purchased in Mississippi would have a higher moisture content than kiln-dried hardwood found in a lumber rack in Arizona. You'll always have some variations due to geography and seasons. The giving up and taking on of some moisture seasonally is what wood does. You can help minimize movement with finish choices that block moisture and encapsulate the wood to some degree, against seasonal humidity swings.
Ideally you'd want your wood to be acclimated to the same humidity level where the finished piece of furniture will reside. Setting aside geographical humidity levels around the country for the moment (and seasonal swings in outside humidity), suffice it to say most folks that can afford to do so, live year round in homes with a HVAC controlled environment. A standard level of humidity of comfort would be between 45% - 55% relative humidity inside a cooled and heated living space year round.
If you kept your wood shop at those levels year round, the kiln-dried lumber in the shop, would then be well acclimated to standard humidity levels of its final resting place, once you build with it and install the finished piece into a home with climate control. The furniture you build would experience the least amount of wood movement as a result. That's a "perfect" world scenario. For most of us, if we start with quality kiln-dried lumber and avoid wild swings in ambient humidity while storing and building with the lumber (ie. our shops are NOT located in a rain forest), things usually work out OK.
The furniture that lasts for generations is built with joinery and methods that can account for some minor seasonal movement. Allowing the wood so it can "move" slightly, versus pinning it rigidly in place (like how you decide to connect a wide table top to a leg trestle base) is paramount to not having joinery/ wood failures down the road. Construction methods matter more than any few points of moisture reading one way or the other on the wood you are working with.
Now if you try to heat and cool a 14 ft x 28 ft shop 24hrs / 7 days a week year round, all your money may go to the electric company with nothing left over to buy wood (or food)! So you try to find a happy medium. You can put a humidity sensor in your shop to see what the relative humidity happens to be when you're not running the AC or heat. You probably already have an idea how humid it is based on how it feels in the shop without the A/C running, compared to your climate controlled living space.
Here in Atlanta, in my non-climate controlled, smallish, two car garage, I run a dehumidifier around the clock. It helps protect tools from condensation moisture and rust. The air temperature is hot in the summer in my garage as a result (I use a box fan when I work). I've run a hose under the garage door so I don't have to empty the dehumidifier reservoir. The cost to run the dehumidifier is less than a standard HVAC cooling the entire space (if I could do so). Because I don't live in the garage (I'm on good terms with my spouse), I don't need to cool the space, I just want the air to be drier for the sake of everything stored in the garage (lumber, tools, old paper files, pallets of toilet paper and taco chips, etc.). That being said, if I could flip a switch and cool the space while I work, that would be very desirable on hot summer days!
You could consider a room dehumidifier for the space during the time you are not working. Or maybe a programmable thermostat could help so the shop space stays at least a little cooler and less humid than the outside at all times (during the warm months), while keeping the electrical meter from spinning full bore. You could also consult with an HVAC expert. There may be a modification / addition available to your HVAC system to allow it to pull moisture from the air, with less cost than full blown air-space cooling. (The relative humidity level of where you live can dictate what solutions may be available.)
Consider getting a decent lumber moisture meter. You can check the lumber before buying and measure the moisture of it over time in your shop. You may find the lumber is actually just fine to build with year round and the only reason to condition the space a bit more is so it's more enjoyable for spending long periods of time woodworking there!
Lumber Check Moisture Meter
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