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Wood and Moisture
The winter of 2003 was colder, wetter and longer than any
in recent memory. The calls at our company about how to read
moisture in heart pine started increasing in early December
as the rains and frosty temperatures set in.
As manufacturers, we have to know how to read our antique
woods on a variety of moisture meters, a skill that came in
handy when customers started telling us concerns like, “It
says 26 percent on one side of the board and 12 percent on
the other.” The highly resinous areas in original growth
heart pine can fool even the best meters, and people needed
to know how to interpret the measurements.
At a friend’s suggestion, we acquired some inexpensive
meters. And sure enough, this winter we needed them. In our
area, some experienced flooring professionals still don’t
have meters, so we were happy to provide them with loaners.
Any meter is better than none if you know the proper setting
for the specie and are told how to account for temperature,
humidity and unusual situations. And, of course, you have
to follow guidelines.
One fellow who called us had stacked several boards together
with stickers between every few boards in a hot, dry house.
The boards stacked without stickers between them acclimated
unevenly and created variation from the middle of the board
to the ends that hung out from the random lengths. There were
freezing temperatures outside that resulted in drier conditions
inside. In addition, the humidification system was down part
of the time, and the wood was very wide and long. This installer
could have saved a lot of money had he gotten accurate readings,
stacked boards correctly, and achieved the right moisture
and humidity.
Yet another fellow who called was gluing and stapling wide
boards over radiant heat. NWFA clearly states that gluing
and stapling wide plank wood over radiant heat is not recommended.
In this case, the wrong setting also was used on the meter,
and the moisture turned out to be 4 to 5 percent instead of
the 8 to 9 percent the installer thought he had. The floor
looks great now, after the installer had a lot of unnecessary
expenses to correct problems from the extreme moisture conditions.
Getting accurate readings, then racking the floor and covering
the boards to acclimate before installation could have avoided
problems and expense.
If moisture and wood sound like a tricky combo, that’s
because they are. After listening to a friend who I thought
knew everything talk about how much he was learning during
a wood floor inspection course, I decided to drive up to Dalton,
Ga., to hear more. The instructor, Howard Brickman, took us
over to meet the rest of the class, including several Mohawk
employees. I knew they were taking moisture seriously when
their national claims manager told me Mohawk is now milling
wood at three different moisture contents for shipment to
different regions of the country.
Contractor Andrew St. James recently moved from Boston to
start Showcase Hardwood Floors in Port St. Joe near the Florida
beach. To learn more about Florida’s specific conditions,
he met with longtime Florida installers Gary and Gail Smith
of St. Augustine. The story that stood out the most was about
an errant nail in the plumbing that caused water to run between
the moisture barrier and the wood floor. The homeowners weren’t
crazy about the resulting mushrooms growing under the furniture.
In another case, the homeowners were told that the floor had
been nailed too tightly, yet the moisture meter proved the
plywood subfloor was at 28 percent. There was moisture under
the house due to no barrier, bad grading and improper ventilation.
Builders can create moisture problems, too. The flooring professional
had to hire an inspector, since the builder blamed the installer.
“Buildings are built very differently than they once
were,” according to Anton Tenwolde, research physicist
at the Forest Products Laboratory in Madison, Wis. “We
are struggling with moisture and wood in the house. Historical
records of moisture content were performed in the 1940s. There
is a map of humidity for various climates that was produced
then, and we really haven’t progressed much beyond that.”
Tenwolde says the FPL now cautions people about the data
in the Wood Handbook on their Web site ( www.fpl.fs.fed.us),
because when it was published, there was little air conditioning,
and buildings were not nearly so tightly constructed. “The
map values are now the extreme values,” he says. He
notes that, except for south Florida, all the data today is
anecdotal. In south Florida during the hottest part of the
year, the humidity is 50 to 60 percent, yet the humidity can
shoot up to 70 to 80 percent for a period of time when the
air conditioning goes off. “This is not, however, what
is in the Wood Handbook. The winter data is still pretty good
for the cold climates. Then again, some buildings have humidification
systems and others don’t. Newer humidification systems
have better controls than those installed only a few years
ago,” Tenwolde said.
Reaction to moisture changes can be more extreme in plantation-grown
woods, an expanding segment of the market, making it more
important than ever to hit the right moisture reading at installation.
The Forest Products Laboratory now recommends moisture between
8 to 11 percent in the South and 6 percent in the dry Southwest,
for example. But, he cautioned that the final number should
be based on average conditions that will exist in the building.
How careful you need to be depends on several individual
assessments, including the type of HVAC, how is it controlled,
summer humidity versus winter, if the house is built with
air tightness, if the concrete is still curing, and if there
is insufficient dry out. The moisture introduced by other
building trades and moisture from building materials exposed
to the rain also should be considered.
The bottom line is that there is more variation in buildings
than there used to be, and most of the old recommendations
are still the best. Make it a point to become educated in
the important factors in each wood floor installation. Scientists
have studied the shrinkage and swelling of wood as humidity
changes for decades. Moisture-related problems are the most
common complaints in the wood flooring industry. In addition
to the Forest products laboratory, the forest Products Society
(www.forestprod.org), a non-profit organization, can be a
valuable resource, offering books and CDs covering wood science.
Wood flooring professionals also have received technical help
from state-sponsored colleges with wood science departments.
As always, make your own assessments of conditions and risks,
follow manufacturers’ recommendations, be prudent and
go for it.
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