Acclimatization of Hardwood Flooring III
So first remember that acclimatization of hardwood flooring is
the process of letting your hardwood come to equilibrium with
the moisture content in the room or home of installation. Read
Part I (should
you acclimatize in the first place) and Part II (
how would you do it if you could?) of this dialogue if
you haven't already.
So I promised to tell you why hardwood flooring installation
should ONLY begin when the moisture content of the wood is equal
to your average moisture content of your home year round....
"average" being the important word.
By average I mean if you have dry winter weather and the relative
humidity in your home in January is 35% then this is your low
end of the relative humidity (RH) scale.
At the opposite end of the spectrum is the hot and humid weather
in August, at least in my part of the world. Temperatures can
get up to as high as 90°. But remember we are NOT really talking
about temperature (hot or cold) but rather the humidity index.
In Northern Ontario the humidity in August can stay in the 65%
range, so the question to ask is; " What is the relative
humidity in your home?." If you have air conditioning it
is going to be significantly lower then outside. Lets suggest
that it is 55% indoors.
That would make your highs equal to 55%RH and your lows equal
to 35%RH. Note I've try to keep the math simple.
This leaves us with a yearly average of 45%.
So why do we want to equalize our hardwood
flooring to this average relative humidity of 45%?
I'll try to explain that by telling you what happens if you don't
do this, and hopefully it will make sense.
Lets say you are installing hardwood flooring in January and the
air humidity is 30%. You do what you are told and spread out all
this flooring across your living room and wait. Optimistically
it all dries to 30% and you install it.
Now its August. The humidity has risen to 60%. Remember you installed
all this flooring after it had shrunk to 30%.. its smallest size
of the year. Now its 60% and the wood wants to expand. Where does
it expand to? The only thing it CAN do is spread outwards where
hopefully you have left enough expansion space that it won't get
jacked against any walls or other flooring.
This puts a lot of stress on your nails and tends to loosen their
connection with the subfloor.
Here's the opposite. You have laid out all the hardwood flooring
across the same floor but now the humidity is at the upper extreme.
The wood swells to its largest size. Now what happens?
You install the flooring in this expanded state. We hit January.
Winter dryness strikes again and you get gaps! The floor boards
have shrunk to their smallest size. You get on the phone and start
yelling at me that either my product is defective or the installation
was incompetent. But nature has taken over and wood has reacted
as wood will! Relative humidity goes down and wood shrinks!
So Why Average?
It might now be obvious. If you install your flooring at its average
moisture level then through the process of seasonal expansion
and contraction the wood and the nails that are holding it in
place only move half the distance.
In summer they expand from 45% average to the high of say 55%.
In the winter they move from the installation average of 45% to
the low of say 35%.
When you install your hardwood flooring at the average, each
board at the time it is nailed into place takes up the space it
needs for the middle of its humidity range. This puts less stress
on the hardwood flooring nails and less compressive force on the
tongue and groove edges in the summer, reducing the odds of large
gaps between boards of hardwood flooring.
I hope this makes sense to you .. but now you understand why
I think effective acclimatization is next to impossible. If you
wanted to achieve these results then you would have to have the
relative humidity in the room where you have spread out all your
flooring equal to the average.
Is that possible? Certainly not if this is a hardwood floor
installation in January in my part of the world!
Hardwood Flooring Installation Techniques