WOOD DOCTOR’S Rx
by Gene Wengert
ewengert@wisc.edu
Color matching maple
cabinet pieces
Checking and splitting in
unfinished chairs.
Q:We are just now getting into ma- ple cabinets and have a problem. We can color match the pieces
but when we put them into a door,
sometimes one piece will look like it
is not even close in color to the other
pieces. Yet we know that they did all
look alike. This is before finishing;
the same is true after finishing.
Second question: We sometimes see
maple that seems weak and does not
hold screws in the hinges well.
Species Density Strength
Sugar 40 15,800
Black 36 13,300
Bigleaf 31 10,700
Red 34 13,400
Silver 30 8,900
Comparison of the five maples
Hardness #/cu ft psi
1450
1180
850
950
700
The five species of maple each have different properties. Density is expressed here
in pounds per cubic foot; strength in psi and hardness in pounds per cubic foot.
A:The angle that you view maple from, especially soft maple, will
result in different color. That is, if you
rotate a piece 180 degrees end-for-end
(or even 90 degrees) and view from the
“other side,” it will appear different. This
is a characteristic of maple. A finishing
specialist would have to tell you how to
cancel this natural effect using fillers,
stains, etc.
Regarding maple properties, I suspect that you are seeing a species difference and perhaps some normal variation
within the species. There are five
different species of maple and each has
different properties. The five are sugar
maple, black maple, bigleaf maple, red
maple and silver maple. Sugar and black
are sold together as hard maple. Bigleaf
is usually sold alone as it grows mainly in
Washington and Oregon. Red and silver
are sold together as soft maple.
Most strength properties are related
to density of the wood. So, here are the
8 percent MC density values: sugar, 40
pounds per cubic foot; black, 36 pcf;
bigleaf, 31 pcf; red, 34 pcf; and silver,
30 pcf. Ultimate strength (MOR) values
are sugar, 15,800 psi; black, 13,300
psi; bigleaf, 10,700 psi; red, 13,400 psi;
and silver 8,900 psi. Hardness values
are sugar, 1,450 pounds; black, 1,180
pounds; bigleaf, 850 pounds; red, 950
pounds; and silver 700 pounds.
Although I do not know of anyone
asking for only sugar maple without any
black maple, soft maple buyers will often
ask for silver maple only with no red
maple.
Q:We have received several hundred unfinished maple
chairs and cabinets from a company located outside the United
States. We noticed that the items
are checking, splitting and cracking
after the finish is applied. I checked
the moisture content this morning
and the range is 9-12 percent MC.
Can we put these in our dry kiln
with just the fans on and dry these
chairs? How long would that take?
Should we add steam? We feel that
8-9 percent MC would eliminate the
splitting.
A:First, we know that if you see cracks, or if the wood changes
size or shape, it is due to moisture
changes. So, you are indeed correct
that the pieces were made at an excessively high moisture content for the
environment where the items are now
being kept.
If, after the wood has cracked,
which means that the wood has lost
some moisture already, and you find 9
to 12 percent MC, we know that prior
to cracking the wood was even wetter.
If the cracks are quite large, then the
wood was substantially wetter than 9
to 12 percent MC. We know that wood
products in most interior locations
in North America average about 7
percent MC, which is about 38 percent
RH. In the summer, we may see 8 to 9
percent MC and in the winter, 5 to 6
percent MC. Your suggested target of
8 to 9 percent MC might be a bit high...
there will be some additional shrinkage
(cracks will grow, maybe some warp,
etc.) that will occur during the heating
season.
I do not see how drying the pieces
in a dry kiln will result in any difference
in shrinkage compared to drying the
pieces in an interior environment. (One
