Cupping and Crowning Continued
CONVEX CUPPING
("crowning") of the floor surface may also occur for all the reasons previously
described, but most often the reason is a different one. It usually follows
cupping of the concave type, which often occurs before the house is ready for
floors to be sanded and finished. If the flooring is sanded with boards cupped
and edges high, the high edges of boards are cut flat by the sanding machine if
the operator does his job correctly. In profile, after sanding, the boards will
then have abnormally thin edges -- flat on top, with edges of the reverse side
of boards still curved upward, or cupped.
If these boards later dry and flatten to their original position, the thin
edges recede, leaving the top of boards convex (edges lower than the centers)
and the back again flat against the subfloor. (Fig.l).
NORMAL CUPPING Some cupping should be considered normal,
especially in wide planks -- 5", 6", 7" and wider -- and particularly in
plain-sawn boards. In such boards (as opposed to quarter-sawn; see Fig. 2) the
growth rings of the tree travel in a slightly curved pattern from one side of
the board to the other. This curved pattern produces, with normal moisture
content changes, a slight convex or
concave cup, depending on how the rings
curve within individual boards.
This type of cupping is usually not noticeable unless the floor is viewed
across the boards and against a strong, low light source, such as a patio door
or window wall. It is often noticed while the house is still unoccupied but
furnishings usually make the cupping seem more normal as the strong light
reflection is softened and angles of view are changed.
SOLUTIONS -- CUPPED FLOORS.
Cupped floors have gone through
a site-related moisture escalation. Re-dried and repaired, the floor already in
place is, in most cases, the best choice for a trouble-free floor in the
newly-established environment. Replacing a cupped floor is usually the worst
choice, especially if replacement is made before the moisture condition causing
the problem has been corrected. The replacement is almost certain to react to
the moisture situation by cupping, like the first floor, and the whole process
must be repeated.
There are, of course, exceptions, when the only solution is to replace the
flooring. But the problem has usually reached a far more serious level before
replacement is needed.
The first step in repairing a cupped
floor is to remove the source of moisture. To cure it the source must first be
found.
In crawl-space or concrete slab subfloors, be sure all outside drainage moves
rainwater away from the house. Water flows through many types of soil almost as
rapidly as on the surface of the ground. If the building sits on a hillside the
natural flow of water may take it under the foundation in large volume, where
some will evaporate. Close this source by installing soil tile on the high side
of the building to drain subterranean water around the house. Generally regrade
if necessary to move water away from the house.
In crawl-space construction lay 6-mil polyethylene film over the entire area
of earth (or concrete or whatever surface exists), weighted down with bricks to
prevent its shifting in a breeze. Be sure the entire area is ventilated on all
walls and that vents are open. If there are dead ventilation areas provide
mechanical means, either temporary or permanent, to circulate air. A
humidistat-switched automatic fan, with a tunnel to an outside vent, is one such
arrangement; coupling the fan to the air conditioning/furnace fan is also a good
arrangement.
CUPPING & CROWNING PART
I | CUPPING & CROWNING CONTINUED
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