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Wood is a natural product
which is hygroscopic, which means it absorbs and gives off moisture,
which causes the wood to expand or shrink depending on the moisture
content of the air and surfaces the wood comes in contact with.
For this reason the moisture content of not only the wood but of all
surfaces around the floor and the air in the area where the flooring
is to be installed has to be regulated. Moisture content of wood
flooring is measured with a moisture meter. These are available
from Delmhorst Instrument Co. (800-222-0638)
or Wagner Electronic Products Inc. (800-585-7609).
Our
flooring is dried to 6% to 8% moisture content. According to
NOFMA specifications, this figure may be higher or lower by
5%, so moisture content must always be checked before installation and
compared with surfaces in the area where the flooring is to be
installed. Installers need to understand the dynamics of moisture and
wood and make educated judgments about when and how much acclimatizing
is required. This could be around one week or longer, depending on
moisture conditions.
Once the flooring has been
installed the least movement of the wood will occur when the interior
environment is controlled to stay within a relative humidity range of
30 to 50 percent and a temperature range 60 to 80 degrees Fahrenheit.
Using an air conditioner and humidifier this range can quite easily be
maintained. |
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The chart below indicates the
moisture content wood will likely have at any given combination of
temperature and humidity. Note that equilibrium moisture
contents in the recommended temperature/humidity range (shaded
area) coincide with the 6 to 9 percent range within which most
hardwood flooring is manufactured. Although some movement can be
expected even between 6 and 9 percent, wood can expand and shrink
dramatically outside that range.
Moisture content of wood at
various temperatures and relative humidity readings.
Temperature (°Fahrenheit)
|
30°F |
1.4 |
2.6 |
3.7 |
4.6 |
5.5 |
6.3 |
7.1 |
7.9 |
8.7 |
9.5 |
10.4 |
11.3 |
12.4 |
13.5 |
14.9 |
|
40 |
1.4 |
2.6 |
3.7 |
4.6 |
5.5 |
6.3 |
7.1 |
7.9 |
8.7 |
9.5 |
10.4 |
11.3 |
12.4 |
13.5 |
14.9 |
|
50 |
1.4 |
2.6 |
3.7 |
4.6 |
5.5 |
6.3 |
7.1 |
7.9 |
8.7 |
9.5 |
10.4 |
11.3 |
12.4 |
13.5 |
14.9 |
|
60 |
1.3 |
2.5 |
3.6 |
4.6 |
5.4 |
6.2 |
7.0 |
7.8 |
8.6 |
9.4 |
10.2 |
11.1 |
12.1 |
13.3 |
14.6 |
|
70 |
1.3 |
2.5 |
3.5 |
4.5 |
5.4 |
6.2 |
6.9 |
7.7 |
8.5 |
9.2 |
10.1 |
11.0 |
12.0 |
13.1 |
14.4 |
|
80 |
1.3 |
2.4 |
3.5 |
4.4 |
5.3 |
6.1 |
6.8 |
7.6 |
8.3 |
9.1 |
9.9 |
10.8 |
11.7 |
12.9 |
14.2 |
|
90 |
1.2 |
2.3 |
3.4 |
4.3 |
5.1 |
5.9 |
6.7 |
7.4 |
8.1 |
8.9 |
9.7 |
10.5 |
11.5 |
12.6 |
13.9 |
|
100 |
1.2 |
2.3 |
3.3 |
4.2 |
5.0 |
5.8 |
6.5 |
7.2 |
7.9 |
8.7 |
9.5 |
10.3 |
11.2 |
12.3 |
13.6 |
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5%
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10%
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15%
|
20%
|
25%
|
30%
|
35%
|
40%
|
45%
|
50%
|
55%
|
60%
|
65%
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70%
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75%
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30°F |
16.5 |
18.5 |
21.0 |
24.3 |
26.9 |
|
40 |
16.5 |
18.5 |
21.0 |
24.3 |
26.9 |
|
50 |
16.5 |
18.5 |
21.0 |
24.3 |
26.9 |
|
60 |
16.2 |
18.2 |
20.7 |
24.1 |
26.8 |
|
70 |
16.0 |
17.9 |
20.5 |
23.9 |
26.6 |
|
80 |
15.7 |
17.7 |
20.2 |
23.6 |
26.3 |
|
90 |
15.4 |
17.3 |
19.8 |
23.3 |
26.0 |
|
100 |
15.1 |
17.0 |
19.5 |
22.9 |
25.6 |
| |
80%
|
85%
|
90%
|
95%
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98%
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Charts taken from Wood
Handbook: Wood as an Engineering Material, (Agriculture Handbook
72), Forest Products Laboratory, U.S. Department of Agriculture.
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Acclimatization procedure |
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Find out the moisture content
for flooring installations in your area of the country. You can
do so by contacting us,
NOFMA or NWFA. Once you have
this range you need to measure the moisture content of the hardwood
flooring and acclimatize accordingly. If the flooring is dryer
or wetter than the range specified for your area you need to get it
within that range by exposing the wood to the air
in the room where the flooring is to be installed. |
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When the packs of wood arrive at
the jobsite the humidity and temperature must already be at the
required settings. The flooring must be removed from its
packaging material and in some way exposed to the surrounding air.
This can be done by placing the flooring on stickers, long strips of
wood about 1" wide and 1/2" thick. These are spaced about 12"
apart and the flooring is laid across them. As flooring is
usually random length this is not the easiest method. Laying the
flooring boards against a wall so that they have air circulating all
around the board is an effective way to acclimatize the wood.
See picture below. After a day or two the moisture content must
be checked to see how the wood is reacting. Once the specified
moisture content is reached the wood is ready for installation in the
area where it was acclimatized. |
Flooring stacked with wooden
stickers in between to get air in contact with all surfaces of the
flooring. |
This photo shows 3' long Gingerwood
flooring being acclimatized. The same can be done with random
length flooring. |
