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Q: I was careful about following correct installation procedures, but the floor I installed six months ago cupped. Why?
A: For the most part, cupped and crowned floors have very little to do with how they are installed, and more to do with when they are installed and what happens to them after installation.
The most common cause of cupping is from severe water leaks. Typically, broken water lines from appliances like refrigerators, dishwashers and washing machines are the main culprits. There is not a lot a flooring contractor can do to prevent these kinds of problems, and fixing them can be areal challenge.
The first step in repairing a cupped floor is to make sure the moisture levels are acceptable for the geographic location. Too often, the terms of the contract or the homeowners dictate that this process be rushed, putting the flooring contractor under pressure to sand the floors before allowing adequate drying time, which could cause even more damage. In some cases, grain crush can occur, which means that the fibers in the wood maintain the cupped shape. If you sand a cupped floor without grain crush, and moisture still is present in the wood, it most likely will result in a crowned floor six months to a year later. The bottom line is that you should never sand the floor while the moisture levels are high. Once a moisture test has been performed and the moisture levels are within the average range for your geographic location, you can begin sanding and repairing the floor.
There are cases where cupped floors are not the result of direct water damage but, again, high moisture levels are to blame.
Just about every contractor learns early in his or her career to put the wood on the job site to acclimate before installation begins, but contractors often are pushed to skip or rush this process by stressed-out retail store owners or anxious homeowners. Skipping this acclimation process can be a big problem down the road, however, as frequent calls to the NWFA's technical department indicate. In fact, this is the type of call we receive most often, so let's review the proper acclimation process.
The first thing we need to understand is that wood is hygroscopic, which means that the wood will gain or lose moisture until it is in equilibrium with the humidity and temperature of the environment it is in. Therefore, the first step to proper acclimation is to get the job site as close to normal living conditions as possible, including proper moisture content in the subfloors. In other words,the relative humidity in the installation area needs to be within the average yearly range for the home.
This can be a challenge if the installation is to occur during the winter, when the heat will be running and the home is closed up. These conditions can cause a drier than average moisture content. For example, if the job site has a 25 percent relative humidity with the heat running and no humidifier hooked up, acclimating your flooring material under these conditions can cause the wood to have a lower than average moisture content. When the humidifier is running, or the season turns to spring or summer, the moisture content will go up and will cause the moisture content in the wood to rise and possibly cup.
The best solution is to get the job site to a controlled environment and test the wood. You should check several pieces of wood from several bundles to get the most accurate readings. If the average moisture content in the wood is 8 percent, and the average relative humidity is 45 percent, and the wood is on the job site under these conditions, you can begin the installation process without the so-called two-week acclimation period. However, you also want to verify that the moisture levels in the subfloor are acceptable as well.
One of the most common problems a flooring contractor faces during construction is that the building contractor wants the floor installed immediately. Perhaps the materials are in the way or the building contractor is behind schedule in other areas. Whatever the reason, the flooring contractor should use this opportunity to educate the building contractor about potential problems. Show him or her how a moisture meter works, explain what it is measuring, show what it means when the floor is too wet or too dry, and identify the problems that can occur if the subfloor has a moisture content of 18 percent. It also can be helpful to show the contractor facts and figures for what can happen when moisture content swings more than 2 percent, such as cupping or excessive gaps. A little education and planning can go a long way to avoid costly and time-consuming repairs down the road.