The Problem
I was
called to repair a gym floor previously installed at an elementary school here
in the Pacific Northwest. The entire gym floor showed signs of cupping; however,
there was an area just outside one of the keys on the basketball court where the
cupping was more significant and the floor, when stepped on, felt as though it
were starting to lift from the concrete subfloor.
The
Procedure
The
new elementary school and the gym floor had been completed in the summer. The
strip maple flooring was installed over a concrete slab overlaid with 6-mil poly
and two layers of 1/2-inch plywood stapled together with rubber cushions spaced
1 foot on center. The wood floor was sanded and finished with four coats of
waterborne gym finish. Several months later, in winter, there was a roof leak,
but there was no evidence of cupping at that time. I was called in when the
cupping appeared in the spring. Everyone at the school was convinced the roof
leak was causing the moisture issue.
The
Cause
As I
drove to the school, I could see it was located at the base of a mountain. I
noticed there was a lot of standing water in an adjacent field. It hadn’t rained
in awhile, but in this area in spring, there is snowpack runoff from the
mountains, and it was apparent that the water table in the area was very
high.
In
the gym, the cupped area seemed to fan out from the middle of the floor toward
the interior wall of the gym. The maple flooring moisture readings ranged from
12-15%. I removed an area of maple most severely affected and moisture-tested
the subfloor. The readings ranged from 25-30%. I realized that the high moisture
levels were contained to one spot on the floor. As I started removing the second
layer of plywood subfloor, I could see black holes where the staples penetrated
the first layer of plywood. Removing the first layer of plywood, I noticed it
was black on the underside, indicating excessive moisture.
Once
the plywood subfloor was removed, I found the source of the moisture: a hole in
the concrete and vapor retarder. Typically, when we install wood flooring in a
gym, we plot out the game line grid and core through the flooring down into the
slab and install the anchors for the volleyball posts. At least one of the holes
had been cored in the wrong spot. When the groundwater increased in spring, it
came up through the hole in the slab.
How to
Fix the Floor
There
were no visible signs of standing water or moisture droplets under the poly at
the time the flooring was removed, so the school board decided to fill the hole
with a fast-setting grout and overlay the area with new poly. The area was
re-covered with new plywood, and the maple was spliced back in. The area of
approximately 150 square feet was re-sanded and re-finished, and game lines were
re-painted. There was still visible cupping throughout the floor, but it was
important that there was no further loss of service of the gym. The intention
was to monitor the cupping in the gym and re-address the floor in the
summer.
In the
Future
When
it was discovered that the hole was cored in the wrong spot, the contractor
should have filled the hole immediately and covered the affected area with new
poly. Since there was still visible cupping throughout the floor I suspect that
there might be more than one hole that was cored incorrectly.
