Acceptable Moisture Levels in Wood – Knowing the Moisture Content

Understanding Moisture Content in Wood

How Does Moisture Affect Wood?

Wood EngravingEveryone who works with wood needs to understand how wood interacts with moisture in the environment. Whether you’re a woodworker making cabinets, a wood flooring professional installing hardwood floors, or if you use wood in construction, wood moisture content (MC) should be always on your mind.

Wood is hygroscopic. It gains or loses water moisture as the relative humidity (RH) of the surrounding air changes.

These varying humidity levels of the surrounding air cause wood to not only gain or lose water moisture but to expand or shrink as well. As the humidity increases, the MC increases, causing the wood to expand. As the humidity decreases, the MC decreases, causing the wood to shrink. When the wood neither gains nor loses moisture, we say that the wood has reached its equilibrium moisture content (EMC).

According to Dr. Eugene Wengert, professor and specialist in wood processing at the University of Wisconsin-Madison’s Department of Forestry, wood should be dried to a water MC that’s within two percentage points of the EMC where the wood is going to be used:

Before we explain what this means, let’s make sure we have our definitions down.

  • MC = the wood’s moisture content
  • The EMC (equilibrium moisture content) of the location where the wood is at the moment or the location of where the wood is going to be used = the MC that the wood will eventually attain if it’s placed in that location.

If this is confusing, don’t worry. The chart below will clear things up. Notice that the EMC of the in-use location is the same as the MC:

Humidity of the in-use
location
EMC of the in-use locationCorresponding MC the wood will attain at this location
19-25%5%5%
26-32%6%6%
33-39%7%7%
40-46%8%8%
47-52%9%9%

So, using this chart, we know that in an area of the country where the RH inside a home or office is anywhere from 26-32%, both the EMC of the in-use location and the wood MC kept in that location will be 6%.

This means that wood intended for interior use in this location should not only be dried to around 6% but should be kept at this MC both before and during the manufacturing process.

So, the wood must always be allowed to acclimate or come into balance with the RH of the end-use location. Failure to do this will result in warping, cracking, and other problems after the construction of the wood product.

How Do You Remove Moisture From Wood?

Kiln Drying

Freshly cut wood has a lot of moisture in it. Eventually, this internal moisture will evaporate by itself. However, kiln drying is used to speed up the process. Some of the unfinished wood you see on the market has been kiln-dried to reduce its water MC to around 8% so that it won’t suffer from moisture-related defects like warping and buckling. However, many building materials may have been dried down to about 15% MC.

But, that’s not the end of the story…

Wood MC is always varying. It’s never constant. Wood – freshly cut or kiln-dried – is always interacting with environmental moisture. Therefore, just because the wood is kiln-dried doesn’t mean it has lost the ability to absorb moisture. It will continue to absorb and release moisture until it comes into balance with the surrounding air.

What Level of Moisture Is Acceptable in Wood?

The acceptable MC in wood depends on two factors:

  • The wood’s final use.
  • The average RH of the environment where the wood will be used.

These two factors make it difficult to say anything specific about acceptable wood MC. It’s more important to understand that the wood is kiln-dried down to a certain bell-shaped range of MCs. There will be statistical outliers on both the low and the high end and you’ll want to catch these by using a quality moisture meter.

How Do I Measure Moisture In Wood?

There are two main ways of measuring wood MC: oven-dry testing and moisture meter testing. Let’s go over the basics of each…

1. Oven Dry Testing

Oven dry testing is the oldest method for measuring the MC of wood. The process is time-consuming but produces accurate results if followed correctly. Here’s how it works…

The wood sample being tested is dried in a special oven or kiln and its weight periodically checked. Once the wood sample’s weight stops changing, its weight is compared to what it was before the drying process began. This weight difference is then used to calculate the wood’s original MC.

While oven-dry testing, if followed correctly, offers accurate results, there are a few drawbacks:

  • It takes a long time – We’re talking about hours. The oven drying process must be done slowly or the wood could burn and the test results will be worthless.
  • It will render the wood unusable – It often happens that oven drying over dries the wood to the point where it’s unusable.
  • It requires a special oven or kiln – Most hobbyists who work with wood don’t have an oven that’s capable of producing accurate results.

These three drawbacks mean that oven-dry testing usually isn’t the option of choice for hobbyists who work with wood.

2. Moisture Meter Testing

The fastest way to test the MC of wood is to use a moisture meter. There are two main types of wood moisture meters, pin-type and pinless.

Pin-type Wood Moisture Meters

Pin-type meters use penetrating electrodes and measure the wood’s MC using electrical resistance. Since water conducts electricity and wood doesn’t, the dryness of the wood can be determined by the amount of resistance to an electrical current. Dryer wood produces more resistance than wetter wood.

Pinless Wood Moisture Meters

Pinless meters are non-penetrating and read the MC via a non-damaging electromagnetic sensor that scans the wood. Because pinless meters scan the wood’s surface and cover a larger area than pin-type meters, they provide a more thorough picture of the wood’s MC.

Pinless meters also don’t leave damaging pinholes on the wood’s surface. This makes pinless moisture meters perfect for measuring the MC of things like expensive hardwood floors.

How to Measure MC in Wood with a Moisture Meter?

Pin-Type Moisture Meters

The general process for using pin-type moisture meters is as follows…

  • Insert the pins into the surface of the wood you want to test.
  • Make sure they’re aligned with the grain and not across it.
  • Turn on the meter. The electrical current will then move from pin to pin and measure the resistance encountered.

Pinless Moisture Meters

Pinless moisture meters are even easier to use. Just press the scanning plate against the wood’s surface, turn on the meter, and receive the reading.

How Accurate are Wood Moisture Meters?

The ASTM D4442 standard determines the accuracy of wood moisture meters. This method uses the oven-dry method and then compares the results to those obtained using a moisture meter. The difference is the moisture meter’s measurement error.

For more information, see our article comparing Pinless Moisture Meters vs. Pin Meters.

MC of Wood from a Woodworker’s Perspective

Wood EngravingBecause wood shrinks and warps as it dries, woodworkers want it to be pre-shrunk before they use it. Furniture maker Lonnie Bird weighs in,

“I don’t want the wood to shrink after I use it because the wood will warp or split.”

Bird, who runs the School of Fine Woodworking outside Knoxville, Tennessee, says he knows wood shrinks seasonally but wants to minimize the shrinkage and expansion by drying the wood to an MC of about 8%.

To make sure the wood is properly dried, he always uses a moisture meter before working with it.

The MC of freshly cut wood is typically somewhere between 40-200%. If you’re wondering how wood can have a 200% MC, here’s how that works…

Because the MC of wood is equal to the weight of the water in the wood divided by the weight of the wood without the water, it’s possible for the MC to exceed 100%. In other words, the water weighs more than the wood fibers.

The normal MC of wood (or EMC) varies from 7%-19% depending on the RH in the air.

For woodworkers who build cabinets, fine furniture, musical instruments, dishes, toys, decorative art, boat restoration, or various other wood products, the acceptable wood MC normally ranges from 6% to 8%.

However, this range will vary slightly according to the geographic region because of varying RH levels.

If an interior location has an average RH of 40-52%, wood placed there will have an average EMC of 8-9%. This is based on a chart in Wood Handbook: Wood as an Engineering Material.

Therefore, in order to avoid post-construction problems, a woodworker building a cabinet for this particular interior environment would need to dry his wood to an MC of 8- 9% beforehand and then keep it that dry during the construction process.

The best way to do this is to use an accurate moisture meter.

MC of Wood from a Flooring Installer’s Perspective

The National Wood Flooring Association (NWFA) has specific installation guidelines for wood flooring and how they relate to MC.

When determining the acceptable moisture levels in wood flooring before installation, the NWFA states that the flooring professional should establish a baseline for acclimation. Acclimation is the process for conditioning the MC of wood flooring to the environment where it will be installed.

To establish a baseline for wood flooring acclimation, the installer will need to calculate the optimal moisture level of the wood by dividing the region’s high season and low season EMC. For example, if the expected EMC ranges from a low of 6% to a high of 9%, the baseline MC of the wood would be 7.5%.

The installer should then check the MC of multiple boards and average the results. A high reading in one area indicates a problem that must be corrected.

We really can’t overstress the importance of taking plenty of moisture readings. When you do this, you not only ensure that the entire batch is okay on average, but you’re also far likelier to catch boards that are statistical outliers and could cause problems.

If the MC of the product is well outside the range of optimal MC, the wood flooring should not be accepted because it will lead to shrinkage, bowing, cupping, and other physical problems.

For example, if the MC of the delivered wood is 12% and the optimal MC is 6%, then physical problems will occur during the acclimation process.

Wood with DropletsTo avoid this problem, wood flooring should never be stored where environmental conditions are uncontrolled, such as garages and exterior patios.

As a general rule, with geographic exceptions, wood flooring performs best when the interior environment is controlled to stay within an RH range of 30% to 50% and a temperature range of 60 to 80 degrees Fahrenheit. However, the ideal humidity range in some climates may be higher or lower. For example, from 25% to 45% or from 45% to 65%.

The National Wood Flooring Association (NWFA) has a chart that indicates the MC of wood at any given combination of temperature and humidity. The EMC in the recommended temperature/humidity range coincides with the 6% to 9% range used by most flooring manufacturers during the manufacturing and shipping process. Although some movement can be expected between 6% and 9%, wood flooring can shrink or swell more dramatically outside this range.

Installers should also measure the moisture in wood subfloors and concrete slabs as they can also affect wood flooring. The maximum subfloor moisture level for solid strip flooring or wide-width solid flooring is either 12% or 13%, depending on the manufacturer.

The National Association of Home Builders’ Green Home Building Guidelines for solid strip flooring and wide-width flooring are as follows:

  • For solid strip flooring (less than 3” wide) there should be no more than a 4% difference in MC between properly acclimated wood flooring and subflooring materials.
  • For wide-width solid flooring (3” or wider), there should be no more than a 2% difference in MC between properly acclimated wood flooring and subflooring materials.

MC of Wood and Lumber from a Builder’s Perspective

For most areas of the United States, acceptable moisture levels of wood and lumber can be in the range of 9% to 14% for exterior wood or for building envelope components within constructed assemblies. An MC in this range, therefore, is considered sufficiently dry for exterior in-service wood.

Using wood with an MC above 14% isn’t recommended because it may have detrimental long-term effects on the construction.

In fact, according to M. Steven Doggett, Ph.D. LEED AP, the founder of Built Environments, Inc., wood MC as high as 15% can cause corrosion of metal fasteners and at 16% may lead to fungal growth.

When it comes to the MC of plywood or dimensional lumber, an MC of 17% to 19% reduces the overall strength of plywood, and an MC of 20% or more reduces the strength of dimensional lumber (i.e., lumber cut to certain predefined sizes, such as 2x4s).

A study by Imamura and Kiguchi (1999) showed that wood MC in excess of 20% can cause a 5% loss of nail shank diameter in four years and a projected 25% loss in 30 years. The same study showed a 40% loss in joint strength and concluded that a 20% MC may significantly compromise shear resistance of exterior walls.

When exposed to a constant RH, the MC of wood or lumber will come to equilibrium with its environment, resulting in an EMC for that species of a wood-based composite.

The EMC of wood or lumber exposed to an outdoor atmosphere varies across the U.S. For instance, in the coastal city of Seattle, the EMC of wood or lumber is higher than the EMC of cities inland or in the Southwest.

Seattle’s EMC ranges from 12.2% to 16.5%. In the Midwest, the EMC of wood or lumber in Des Moines, Iowa, ranges from 12.4% to 14.9%.

In contrast, Las Vegas in the drier Southwest has much lower EMC percentages than most other U.S. cities. The Las Vegas EMC of wood or lumber ranges from 4.0% to 8.5%.

Acceptable Moisture Levels for Wood In a Nutshell

Based on common guidelines or recommendations, the acceptable moisture levels for wood are as follows:

  • Wood objects used indoors: 6-8%
  • Wood flooring: 6-9%
  • Construction: 9-14%

Keep in mind that a wood’s acceptable moisture level will depend primarily on how it will be finally used and the average RH where it will be finally used. However, the wood species and the thickness or size of the wood may also factor in.

In all cases, determining the acceptable moisture level of wood requires the use of an extremely accurate moisture meter.

Failure to allow the wood to acclimate or come into balance with the RH at its end-use location could result in any number of moisture-related problems after the wood product is constructed. These include warping, cracking, buckling, diminished wood strength, corrosion of fasteners, and even fungal growth.

56 Comments

  1. Renee Killian says:

    Larry,

    I so appreciate your treatise on this issue.
    My question for you is: after a smallish unheated underground space (similar to a basement, i.e. all concrete) is framed and sheetrocked (though not mudded or sealed in any way) is then the studs are tested for humidity, what would be a reasonable level here in Seattle, living approximately 100 yards Puget Sound? This building was constructed around 1966 and this little space appears very dry, in spite of a recent leak from an nearby hot water tank. The company they hired measured 47% in the ‘wood’ and declares that this must be ripped out and replaced.
    Sorry that this is so long-winded and I thank you in advance if you are willing to address this question for me.
    Thank you,

    Renee

    • Larry Loffer says:

      Hi Renee,

      Standard construction studs such as 2×4 and 2×6’s are typically dried to 19% moisture content before they are installed. Any moisture content measured higher than that might result in movement, such as warping and twisting, once it dries. Also, there is a risk of mold. A wood moisture content of 47% is too high.

  2. Samuel Hau says:

    Hi Larry,

    We are manufacturer of eng wood flooring. My first question is how to determine the MC of eng wood flooring which composite of different species layer, face and different species to form plywood core.
    Example: 1.2mm Hickory wear layer
    9mm thick plywood compose of 7 layers, 2 layers acacia, 4 layers of Eucalyptus\2 layers Acacia and one layer Poplar.
    In this case, what Built in # that I can use to measure flooring.
    2nd question, will lacquer on surface of flooring affect the reading.

    Samuel

    • Larry Loffer says:

      Many of our customers are successfully using our hand held moisture meters on engineered flooring. The thinner veneers won’t have much bearing on the reading. Set the meter to the species that makes up the bulk, in this case, the plywood. The plywood setting is .57. Lacquer will not make a reading difference as long as there are no metallic components in the lacquer itself.

  3. kevin says:

    Hi, we live in a coastal area, had a recent water leak, and a hard wood floor MC is measuring about 25% – the water did not contact this area directly.

    in other hardwood areas that wasn’t close to the water, was measuring about 16-19%.

    our question is do we need to replace the floor to avoid fungal problems?
    Thanks!

  4. Jerry Setzer says:

    Larry: I recently had my annual termite inspection. The inspector said his meter reading taken from my basement on subflooring/joists/framing was too high. (He didn’t cite a figure.) He added that plastic sheet ground covering that his company laid over my crawl space had been moved in spots and that I no longer had full coverage. I live in upstate South Carolina. We have had an abnormally wet spring and part of summer. I suggested replacing my dehumidifier (Sears brand, bucket collection) which has been inoperable this past year. He, of course, said that type of product is insufficient. He wants to install his company’s system, seal all external openings around connections, etc. for a mere $4900. My house was built in 1927. I get some water seepage through an exterior wall at basement floor level as a result of heavy rain. It is a 2-3 feet wide wet area that drains to a line connected to the city system. Generally the entire floor is dry. The air vents stay closed year round. What do you recommend?

    • Larry Loffer says:

      Jerry, From a moisture standpoint, water in the basement can over time absorb into your subfloor. I don’t know what type of floor you have, but if it gets wet enough, about 25% moisture content or higher, mold can grow. Doesn’t sound like this has been a problem in the past. I would think at least fixing your dehumidifier is a must.

  5. Yen says:

    How to test moisture /water content in cassia bark? What is the acceptable water/moisture content in cassia bark?- in south east asia

  6. David Kiemle says:

    Hi Larry,

    My potential house in North Carolina Fayetteville area was just checked for moisture content in the crawl space. The levels were between 20 and 23%. The house was not in the flood area however they did receive 20 inches of rain.
    Do these levels seen appropriate considering the recent rainfall.
    Thank you

    • Larry Loffer says:

      David,

      As long as the moisture content does not exceed those readings you should be ok. Mold starts to grow in the mid to high 20 percent moisture contents.

  7. John says:

    David,

    I am having a section of our 3.25″ Maple hardwood floor replaced. About how long do you think we should allow the new wood to acclimate in the end use environment before installing it?

  8. John Howard says:

    My house is 24 years old. 18 years ago the moist content (MC) of the beams and joist was 24% in an area of the crawl space that floods in spring. I installed a sump pump and 6 mil vapor barrier, but the barrier is not sealed around piers and the ground is moist under the barrier all year. I was able to get the MC down to 15%. I also applied Boracare (boron) that has stopped minor beetle damage.
    Three years ago, the floor sank in a heavy traffic area and an engineer told me Masonite was used to shim and had compressed. Over a year ago, I re-shim all the piers with metal shims. The floor immediately felt stronger.
    Prior to the re-shim, the pier in the area that floods in the spring could be felt pushing up the floor, meaning the beam is warping and been monitoring it. This week, I notice the next pier on the same beam is starting to push up, warping the floor. Knowing were all the piers are, I can stand on top and feel a small hump in the floors. You can hardly see the humps except the first pier that popped up ¼”.
    I had a quick looked around the crawl space and didn’t notice any structure damage. I not sure if this is normal, related to the re-shim or need to install a crawl space dehumidifier to slow the progression?
    Thank You.

    • Larry Loffer says:

      John,

      A dehumidifier in the crawlspace will help but can be expensive. The purpose of the vapor barrier is to keep moisture away from materials that expand and contract. Perhaps try to seal the vapor barrier better around the piers.

      The other thing to consider is examining how water is entering your crawl space. Perhaps better drainage around your house will do the trick… or treat. Sorry, that time of year.

  9. Eric Thoren says:

    I had a water leak under my crawl space which has 3 inches of foam insulation applied to the underside of the sub floor. The water eventually came out a electric outlet located three inches off the floor. I removed an of the foam insulation. The subfloor registered from 12% to 17% . Should I remove more foam to be sure. The engineered wood floor appears ok. I live in coastal South Carolina .we are definitely afraid of mold formation. Any suggestions .thanks

    • Larry Loffer says:

      Eric,

      Is your electrical outlet that is 3 inches above the floor inside the house? Water was coming out of this outlet and onto the floor? If that is the case you need to remove the flooring and examine the subfloor. You should be able to tell where the water reached the subfloor because it will be discolored and may also be swelled up.

      Moisture contents of 12 to 17% is ok. You don’t want to see any subfloor reach about 25% which is where mold will start to grow.

  10. Christian says:

    Hello,
    I am renovating my kitchen and installing hardwood floors. The floor installer put the floors down without allowing the boards to acclimate. When questioned, he said because Room is under 200 sq feet it is not a problem. Is this accurate?

    • Larry Loffer says:

      Christian,

      That doesn’t make much sense to me. The purpose of acclimating is to allow the flooring to equalize to the surrounding conditions, no matter how large the room is. Be on the lookout for flooring failures such as swelling, buckling, cupping, etc.

      If any of these conditions occur, tell your installer right away.

  11. Dana Mcgibboney says:

    Should you check moisture levels on a trailor floor on a massive rainy day? Will the reading be accurate?

  12. Mobeen says:

    If a wooden sample has moisture content range of 2-6% only and if it has moisture content of 9 or 10% then what does this mean??

    • Larry Loffer says:

      Mobeen, If a wooden sample gains moisture, then the sample will increase in size. This can be a problem once installed in furniture or a floor. It is best to allow the wood to equilibrate to the room environment.

  13. Humberto Garcia says:

    Larry,

    I am building a farm style dining table with pecan 2″ thick X 8′-0″ long boards.

    The lumber was recently milled, although the tree had been cut months, years ago.

    What should be the approximate Highest MC to prevent wood problems to include finishes?

    Thank you in advance for your response.

    Humberto from Texas

    • Larry Loffer says:

      Humberto,

      The typical moisture content for hardwoods that will be indoors is 6-9 percent. You will want closer to 6% in the drier climates and 9% MC for the more humid climates. Either one should be acceptable for finishes. It’s always a good idea to check with the manufacturer of the finish also.

  14. John Vilseck says:

    Hello Larry,

    We just bought a home where we discovered the plumbing was leaking over a number years with a kitchen flood occurring in the last 3-5 years due to a busted water line. The water wasn’t properly dried and organic growth was discovered by previous owner. Instead of addressing the plumbing and damaged wood, they installed a dehumidifier in 2015. The home inspector failed to report all the sewage stains on the plastic and organic growth on some of the joists have which had been exposed to moisture the whole time even though the dehumidifier has been mitigating the plumbing leaks. A company sealed off the foundation vents and removed all the insulation from the crawlspace with the humidifier mitigating the moisture from the leaks. Since the cold weather has come on, the organic growth has gone dormant, but a contractor noticed joists with distinctive moisture content where there are definitive separations between dry and wet looking wood. However, the company who maintains the dehumidifier said he tested some of the joist which he said only registered 10 on his device. I don’t know what to believe except the company who installed the vapor and dehumidifier said the vapor barrier needs to be changed out because of all the sewage and drainage stains after the plumbing is fixed. One of his own service guys said foundation caps needed to be replaced. Wonder if they are trying to cover themselves. Live in Tn. The plumbing was improperly installed with the wrong cement to fit the pipes and could have been leaking from anywhere between 5-29 years while absorbing into the ground. Any opinions.

    • Larry Loffer says:

      John,

      If the water leak was bad enough, dry rot can occur causing possible structural integrity issues. Did the Contractor mention anything about the structural strength of the joists?

      One of our new line of moisture meters will help locate areas of high moisture, if it still exists. Mold starts growing if the moisture contents reaches about 25% moisture content. Here is a link to our new line of meters:

      https://www.wagnermeters.com/moisture-meters/

  15. John says:

    Hi Larry,

    Thanks for the reply. There are joists that display splitting. We haven’t gone any further since the condition was found so close to us purchasing the home. So we are seeking redress, but there are jacks present underneath the home which the home inspector didn’t report either and didn’t know if this was extra support for the water heater or what. There are areas where organic growth was very active to cause deep, black discolorization. I will get further testing from those not involved. Thank you.

  16. Jim Kenyon says:

    I have 1 1/2 ” thick cherry boards that I had milled from a tree in my yard last fall.
    They are in an unheated and currently very cold barn
    The moisture ranges from 11% -16% according to my meter.

    What % does it have to get down to before it would be usable to make a table top ?

    Thanks
    Jim

  17. Brian Cook says:

    Larry,

    I found your moisture levels column through a search for “good wood for low humidity”. I think that I know my own answer, but thought I might reach out for some possible better insight. I have built two table tops (douglas fir) that have both suffered major cracking in their final location. I built the tables in west Texas, but their final home is in Colorado. Both times, the tables were flawless, but after 2-3 weeks in their new home both table tops had major crack issues. We found out that RH at the final location was under 20%. RH where they were built is about 29-30%. We are very arid where the tops were built so I figured the tables would be just fine knowing that it is arid where they were going…but that doesn’t seem to be the case. Allowing the wood to acclimate in the final spot before building, really isn’t possible because it is 8 hours away, and I can’t take a week off to go up there and build the table. Any suggestions to this being possible to correct? Different wood? Different joinery (currently using pocket holes)?

    Thank you for your time.

    Brian

    • Tony Morgan says:

      Hello Brian, I am a moisture meter expert, not a woodworking expert but from your description, the problem points to the conditions, not the wood or joinery. Wood is a hygroscopic material, meaning it picks up or loses moisture based on the ambient conditions. There is only so much moisture a piece of wood can give up, over time, before a failure occurs. The failure in your case sounds as though the piece was exposed to a rapid loss of already low ambient moisture, causing the cracking in the piece.

      The optimal humidity in a home is generally 35%-55% and anything under 20% is actually considered unhealthy, as it dries out the skin. It does the same for wood, and is especially hard on softwoods, such as pine or fir. It is not uncommon for wood to expand or contract as much as a 1/8” per foot of width, so maintaining a stable environment is important. If the conditions are too wet, dehumidify, and if they are too dry, humidify.

      I strongly recommend using a moisture meter, along with a thermo-hygrometer, or even a smart logger before you start building, to ensure the wood is at an optimal moisture content in an environment that has an acceptable relative humidity and temperature range. These tools will give you the confidence that you have done everything on your part to ensure the highest quality in the piece you have built.

      Here is a link to our moisture meters, thermo-hygrometer, and Smart Logger.

      https://www.wagnermeters.com/wood-moisture-meters/

  18. Drew Smith says:

    Thank you for your very informative knowledge about all of the items on this page. This summer I milled several 1.25″ boards from a fir log that had been cut around 10 years ago. Moisture was around 25% when milled, and the ends were sealed. The boards have dried nicely so far with minimal warpage or checking. They are currently nearing equilibrium (around 12 MC) and are stored within the house. My plan is to make a wall-mounted headboard out of angle iron and these boards (boards will not be joined). My question is regarding finishing. I have used spar urethane as a finish on a few other 12 to 18 MC (semi-wet) log projects that turned out wonderfully. However, this time I was planning to use oil based poly rather than the spar urethane to reduce the amount of yellowing. One of the beauties of spar is that it allows the wood to move quite a bit, while still retaining good adhesion. Do you see any dangers of using poly with a MC of around 12, or am I risking adhesion failure – especially if the wood does end up shrinking dimensionally? The angle iron will prevent much warping, and I do plan on finishing all sides (and ends). Thank you so much for your time and expertise.

    • Ron Smith says:

      The manufacturer of the oil-based poly should have a specification on the maximum allowable moisture content of the wood. Question: Just to make sure that you get accurate moisture measurements, has your moisture meter been checked for calibration?

  19. Tom Martin says:

    Hi Larry,

    We’re looking to replace the floor in an old (unheated) hay barn with treated tongue & Groove 2×6 flooring and need to know if the advertised 19% MC will be ok and not shrink too much. We’re in northern Indiana, humid summers long cold winters…

    Thank you for your help and any advice!

    Tom

    • Tony Morgan says:

      Treated wood is typically still wet when it’s delivered to the job site. As it dries, you should expect slight changes in width and length. As lumber dries, it may split, cup and warp. This is more likely to occur to occur in lower-grade boards, where knots and uneven grains are already present. Each piece of lumber is unique and carries physical characteristics that may include the following: knots, warping, shrinkage, swelling and/or splitting.

      The normal outside equilibration moisture content (EMC) for Indiana is anywhere from 13% to 16%. There will most likely be some shrinkage, so if possible, choose the clearest boards possible to lessen the possibility of any major cracking.

  20. Jim Labor says:

    I dialed the 800 number for Wagner meters and all I got was two sales pitches for a Life alert type device. The other was for a $100 retail gift card. I wanted to talk to someone at Wagner about moisture guages and is there a dealer near Chattanooga, TN.

    • Larry Loffer says:

      Hi Jim,

      Oh no! We’re so sorry for the inconvenience. Please give us a call at (800) 634-9961 or email info@wagnermeters.com, if you’d prefer. Also, please feel free to provide us with the number that you called so we can make sure that all of our phone numbers are printed/posted accurately!

      Thank you,

  21. Jeff says:

    Hi Larry,
    So a friend of mine has some pine and oak blabs at MC levels of (oak – 11.5%) and Pine 13-14%. Now would the pine be okay to use as a top cover piece to an radiator cover? if not, can you tell me why? Second, would the same pine slab, would it be okay to use for a side table or Kitchen island. I have come across this and haven’t made the purchase from my friend because I am not sure about the warp or breaking it will come.
    Thanks

    • Larry Loffer says:

      Hi Jeff,

      As with any wood product, the environment where the finished product will “Live” will determine the correct moisture content. Moisture content of 11.5% for the oak is a little high for furniture grade hardwoods. Again, the correct moisture content will depend on the surrounding conditions. Wagner has a free app called “WoodH2O” to help you determine the proper moisture levels based on consistent humidity and temperature.

  22. Tapon Chakrabarti says:

    Hello Larry
    I am from Bangladesh. Here current humidity is 76%. What would be the recommended MC for doors of my new building(under construction)?

    • Larry Loffer says:

      Hello Tapon,

      If the humidity is a constant 76% then the wood will equilibrate between 14 and 15% moisture content.

  23. Shirley says:

    Toilet overflowed and moisture meter is reading 30% in worst area. Can carpet be reinstalled?

    • Larry Loffer says:

      Shirley,

      Before installing carpet, you will need to dry the subfloor first.
      If your subfloor is a wood product, make sure the reading is less than 20% on the moisture meter.
      Also, if the leak was bad enough, it will be necessary to have a contractor make sure the strength of the subfloor isn’t compromised.

  24. Rachel says:

    Hi, in MN where extreme temperatures are very hard on homes.
    What do you recommend the reader to be at before insulation and drywall on new construction?
    We have had very bad cracking in sheetrock and floors.
    Thank you

    • Larry Loffer says:

      Rachel,

      2×4 and 2×6 framing studs should measure 19% moisture content or less. This is the standard in the construction industry. Subfloor material such as plywood or OSB should measure between 10 and 14% moisture content.

  25. Kevin K Gardner says:

    My question: what is the complete saturation reading of wood? WME?

    • Larry Loffer says:

      Kevin,

      Percent moisture content in wood is the ratio of the weight of water compared to the overall weight of a piece of wood. A 10% moisture content reading means that 10% of a wood sample’s weight is due to water in the wood. If a board reads 100% (Difficult to measure accurately) then the weight of the water equals the weight of that wood.
      It is possible, in some species, to have a moisture content higher than 100 percent. This means a very absorbent wood can retain more water, weight wise, the weight of the wood itself.

  26. Davetta Goff says:

    hello I been getting very sick in my home so I had my manger do a mold and moisture test which came back high level of moisture levels which a contractor wants to take the sub floor up and 2 to 4 inches of the wall but my apartment manger is not releasing to report and he’s is saying the spore test didnt pick up any mold spore… question is it safe for me and my family to be in the home with high level of moisture in the restroom which the floor have been really soft for over 9 months now as well as the kids bedroom where a pipe burst

  27. ewan macdonald says:

    I have an unusual question, if I was to sandwich recycled paper (similar to hardwood floor paper only heavier) between 2 layers of wood as a draft stop what should the moisture content be to avoid the paper absorbing any water and ending up with a mold issue thanks in advance for any info you can provide

    • Jason Spangler says:

      Ewan:

      Thanks for the question. From a strictly static MC%, 16-20% MC for long duration is going to promote mold growth. Obviously, the ambient conditions within which the wood or paper is present can alter the MC% of the wood or paper. So, when looking at the relative humidity of the space, spaces left above 70% RH for extended periods will also promote mold growth. Good luck.

  28. Barbara says:

    I had engineered hard wood installed and it is curling at the joints. I live on the fl coast so what should the moisture level be?
    I really need to know as I am getting so many different opinions
    Thanks

    • Jason Spangler says:

      Barbara:

      Thanks for the question. A general rule of thumb for the coastal regions of FL would be 11-13%MC. The more specific way to know would be to measure the relative humidity and temperature in your homes air and then plug the numbers into a calculator like this https://www.spikevm.com/calculators/logging/equilibrium.php This will tell you what the MC% should be based on your specific environment. Good luck.

      Jason

  29. Scott Perkins says:

    Working with some slabs of spruce. These are slabs roughly 2′ thick.

    Cut in the spring and stacked and dried them over the summer. I know the rule of thumb is 1 year of dry time per inch of thickness of wood. Spruce isn’t a hardwood so I’m assuming I could get away with a shorter dry time. Currently reading a 12.5%. I have a couple questions. Since I’m drying them outside, being in AK I would like to work with them if possible before the long moist winter.

    1. 12.5% is gettin there but not quite to the 6-9% mentioned in the article. Can I get a away with this?

    2. I would like to rip two slabs and glue them together to make a nice large dining room table. Should I wait for the slabs to be within that 6-9% to cut and glue? Can I a cut them first, then glue them once they are dryer?

    • Larry Loffer says:

      Hi Scott,

      You are correct, furniture grade hardwood is typically dried between 6 to 9%.
      Softwoods, such as spruce, can have more moisture. Your reading of 12.5% tells me it is workable.
      You must be careful with a thick slab once you cut it. If the middle is wet, you may experience cracking/splitting if dried too fast. I would also consider the environment where the table will live. We have a free ‘App’ called WoodH2O that will tell you the moisture content given certain temperature and humidity conditions.

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