How To Check Moisture Content of Wood Without a Meter
Nothing ruins a good woodworking project like gradual warping, shrinkage, or expansion. While a wood type might seem to be a great pick for flooring or furniture based on aesthetics, what you really need to focus on is moisture content. The wetter a wood is, the more vulnerable it’ll be to warping.
Normally, it’s easy enough to check moisture content before using wood for a project. Just use a handy moisture meter! But what if you lost yours or haven’t gotten around to buying one yet? No matter – here’s a guide explaining how to check the moisture content of wood without a meter. It’s simpler than you might think.
Why Check Wood for Moisture Content?
The moisture content (MC) of a piece of wood can affect that wood’s shape and size. As a hygroscopic material, wood absorbs or loses moisture depending on the ambient humidity of its environment. Additionally, wood pieces passively retain some moisture after being felled – depending on humidity, they may eventually or never lose all this moisture.
In more humid air, the wood fibers suck up surrounding moisture – this causes wood to expand. In drier air, wood loses moisture. The reverse occurs as the wood shrinks.
Wood can also reach equilibrium moisture content or EMC, which occurs when wood doesn’t gain or lose moisture.
Woodworkers might want to measure the MC of a piece of wood so it doesn’t shrink and warp after they use it. Thus, they may try to only work with pieces that won’t become too wet over time. Similarly, flooring installers might want all of the wood pieces to be at an MC suitable for acclimation to their building’s ambient humidity.
What Types Need to Be Checked?
Certain types of wood hold more moisture, both immediately after being felled and in general. Broadly speaking, heavier and denser wood types handle more moisture or ambient humidity better since they’re more resistant to warping or breaking over time.
Lighter woods need to be checked more often since they’re more vulnerable to significant weight and shape changes as their MC adjusts – their retained water simply has more of an effect on the shape of their fibers.
Wood Types That Need to Be Checked
- Maple – this wood is very popular in flooring and furniture. It commonly shrinks a bit when used in humid conditions
- Pine – although pine withstands shrinkage and warping well enough, it’s a soft wood that should still be measured for exact measurements
- Spruce – this wood is an excellent finishing type and resists decay quite well, but can also experience shrinkage frequently
- Cedar – this decay-resistant and rot-resistant wood often experiences expansion and shrinkage when exposed to higher humidity air, so its MC should be measured
Mahogany, walnut, oak, cherry, and teak are all relatively durable and heavy woods that resist warping and shrinkage quite well. It’s less important to check the moisture content of these wood types, though it’s never a bad idea.
How to Check Moisture Content
MC can be understood as an expression of the weight of the water compared to the weight of oven-dried wood, then multiplied by 100. Put simply:
- MC = weight of water/weight of oven-dried wood x 100
Understanding this formula will allow you to check MC without using a meter tool.
The formula would look like this:
- MC = 0.8/10 x 100, as 0.8 pounds of the pre-dried wood’s weight was water
- This results in an MC of 0.08 or 8%
The Oven Test
The simplest way to check the moisture content of a piece of wood is to weigh a piece of wood, dry it in an oven, then measure it again to see the difference in weights. This is the most accurate way to test MC in wood, but it’s also time-consuming.
The oven for this measurement method needs to be well ventilated, and the wood will need to be dried for a significant period of time.
Step 1 – Turn your oven on to 220°F or similar depending on your oven’s heating abilities. Again, make sure the oven is well ventilated, or use a kiln. The ventilation is important so the water has a place to escape.
Step 2 – Weigh the wood while the oven is preheating. Write the number down.
Step 3 – Put the wood in the oven for 24 hours. Weigh the wood after this period, then write the number down. The difference in weight between the two measurements is the hypothesized “water weight”.
Step 4 (optional) – You may wish to set the wood in the oven for another 24 hours. If the oven-dried wood’s weight changes, it still needed to dry a bit. If it’s the same as before, you know it’s fully dry. Heavier, wetter woods may need multiple days’ worth of drying before they’re ready for measurement.
Step 5 – Now plug in the formula above. As an example, say that the wood weighed 10 pounds before oven-drying, then 9.2 pounds after.
Put another way, the MC is the proportion of a wood’s weight made up of water. The weight difference shows, out of 100%, how much of that percentage is/was moisture.
What is a Good MC for a Piece of Wood?
This is dependent on your environment and task. However, here are a few guidelines for general MC wood levels you should check for:
- Indoor wooden objects like furniture: 6-8%
- Wood to be used for flooring: 6-9%
- Wood for building construction: 9-14%
The “ideal” MC for a piece of wood will also depend on the ambient humidity of the environment.
Ultimately, checking the moisture content of a piece of wood without a moisture meter is fairly straightforward, if time-consuming. Still, it’s very useful to have this method in case your moisture meter ever breaks. Remember to keep the oven ventilated and to select your wood for your project carefully – heavier, sturdier woods do better in humid environments in most cases regardless of MC. Good luck!
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