Moisture Content vs. Humidity

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Forum topic by Russel posted 02-06-2009 03:02 AM 1719 views 0 times favorited 5 replies Add to Favorites Watch
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2199 posts in 4175 days

02-06-2009 03:02 AM

My son-in-law lays hardwood floors in Phoenix and recently came upon a bit of a problem. A while back, about a year or so, a teak floor was installed. When the floor was put down, the moisture content of the wood was about 6%. (In his area of the country this is considered good.) He recently got called back because the boards had started to separate. When he checked the moisture content now he could not get a reading, meaning a near 0 moisture content. He is thinking that adding a humidifier to the house would bring up the moisture content in the wood, the question is:

What should the ambient humidity be to raise the moisture content to an acceptable level?

Here is Michigan, 8-10% moisture content is generally pretty stable and a 70% humidity seems to be typical. Is there a constant ratio of Humidity to Moisture Content?

Thanks for any insight you folks can provide.

-- Working at Woodworking

5 replies so far

View Julian's profile


880 posts in 3762 days

#1 posted 02-06-2009 03:28 AM

Having a humidifier is a must with a hardwood floor. If the house that he installed the floor in didn’t have one, then he should have had them sign a waiver stating that he isn’t responsible for shrinkage. The humidity in a house without a humidifier in the winter time is drier than a desert.

-- Julian, Park Forest, IL

View CharlieM1958's profile


16281 posts in 4455 days

#2 posted 02-06-2009 04:22 AM

There seems to be a rash of splitting teak. Did you notice this post?

-- Charlie M. "Woodworking - patience = firewood"

View childress's profile


841 posts in 3778 days

#3 posted 02-06-2009 05:45 AM

I don’t think you can say that there is a constant ratio….because your dealing with absolute humidity and relative humdity. saying 70% is relative humidity, but absolute humidity depends on the tempurature of the air. The higher temp means it can hold more water vapor (absolute humidty). Relative humidity is the ratio of water vapor (absolute) to what the air temp can hold. so 70% at 50 deg. has less water vapor in the air than 70% at 75 deg. While wood does reach EMC (equalibrium moisture content) based on relative humidity, the tempurature does play a role. And being in Phoenix, there is severe wheather changes throughout the year. As long as the home stays pretty constant in temp year round, keeping about 30% humidity @ 70 deg. should have an avg. EMC back up to 6% (this info is based on averages, I’m not too familiar with teak though) If you read “Understanding Wood” by Bruce Hoadley, he goes into detail on this stuff. There really is ALOT that I’m leaving out.

-- Childress Woodworks

View GFYS's profile


711 posts in 3707 days

#4 posted 02-06-2009 06:47 PM

Wow wish I had read this thread two months ago. I’m working on a trim out up here in Alaska and we had a very moist year until about two months ago it got very cold and the heat system this place has is infloor radiant tube hydronics. There is absolutely no condensation on any windows or doors. The cabinets I built were moving allover the place. Face front joints broke, base mold joints came apart ( some as much as 1/4”) I have been killing my self keeping up with the fixes. The building is an aircraft hangar with a 1200 sqft living space. The building is so dry there isn’t a drop of condensation even on the metal hangar door frame that is exposed on the inside. I let the lumber I used acclimate for at least two weeks in the building. Should I get a humidifier at this point. Will this lumber swell back any if I do that.

View Russel's profile


2199 posts in 4175 days

#5 posted 02-06-2009 07:12 PM

Thanks for the info. There’s a lot to know and it’s good that folks here know a lot. I’ll pass this on to my son-in-law.

-- Working at Woodworking

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