Bridging the Gaps
Strip floor shrinks after installation
By Glen Miller
I was called in to inspect a 2 1/8 inch solid red oak floor in a new home in North Carolina. The home owners were objecting to gaps that appeared in the floor after they moved into the home.
Construction began on the house in November and it was enclosed in March. Shortly after that sheetrock was installed and the flooring was delivered at the end of April. On May 1, flooring installation began. It was installed throughout the kitchen, dining room, entry, and front bathroom and was over an OSB subfloor and crawlspace. After the flooring was installed it was left for a month and a half before it was sanded and finished. On August 1, the HVAC system was turned on and the home was occupied in the middle of August. The gaps appeared in October continued to get larger throughout the winter months and never closed the following summer.
I took board measurements throughout the floor and found that they ranged from on size to 1/8 inch under. The board runs of 20 boards which should have measured 45 inches averaged about 45 1/2 inches. The moisture content (MC) of the flooring at the time of inspection averaged from 8.5 to 9 percent, while the subfloor MC ranged from 10.5 to 11 percent. The fastener schedule was within recommendations and an inspection of the crawl space found that it was completely covered in plastic, with no standing water or other moisture problems caused by shrinking after the flooring absorbed extra moisture before installation, the floor at the time of installation was wider than at the time of manufacture. After installation, site conditions added to and maintained these high moisture conditions. The occupied enviromental conditions were not established until just prior to move in, and general enviromental drying associated with occupancy and seasonal heating caused loss of moisture and associated shrinkage.
How to Fix the Floor
Gaps up to 1/4 are considered fillable when no movement is present among the boards and only two gaps in this floor measured greater than that. The options for those two gaps were to either install shims (or "slivers") or to install new boards those areas. If only filler is used its sometimes possible to just screen and recoat that area of the floor. But since this floor had gaps throughout the entire floor and two areas that had to be slivered the entire floor was resanded, filled, and recoated. Also it was recommended that this be done when the temperature and humidity were seasonably moderate and the flooring would be at a MC midpoint such as in October or May.
In the Future
Be sure the heat or air conditioning is on before installing the flooring and be sure to acclimate it properly. A lot of people think acclimating means you take the flooring to the job site and leave it there for four of five days. Proper acclimation for strip flooring (less than 3 inches wide) simply means that the MC of the flooring and the subflooring are within 4 percent before you install the flooring, moisture tests with a moisture meter must be taken and the environmental conditions should also be taken into consideration. It's possible that strip flooring is already acclimated the second you bring it in the house as long as its MC is within 4 percent of the subfloor MC.
Glen Miller is assistant technical training director at the National Wood Flooring Association