Hardwood Floor Cupping And How To Deal With It

Hardwood floors are among the most beautiful types of floors on the market, but they are seriously affected by moisture. One problem that they often suffer from is cupping. This occurs when moisture warps the center of the board to make it higher than the edges. This serious problem makes an uneven floor, but it can be repaired.

When Cupping Is Serious

Wood floors will naturally swell and shrink with changes in their moisture, with swelling occurring when moisture is between 0% to 25%. When it's higher than 30%, wood is more stable. So if your moisture level falls in this range (which you can check with a wood-moisture gauge), your hardwood will start to swell and shrink.

But it won't change shape equally in all directions. Typically, moisture content between 0% to 28% will cause the board to grow 0.1% lengthwise and 5% to 15% in width. This is when you are most likely to see your most severe cupping.

Identifying Causes Of Cupping

If your hardwood floor was installed properly, then cupping is typically caused by a variety of problems. Some of the most common of these problems include low indoor humidity, moisture imbalance in the wood, spilled water from a bathtub or dishwasher, plumbing leaks directly onto or underneath the floor, and other problems that change the moisture level of a floor.

Identifying which problem is at fault is simple. Start by testing the moisture level of the floor and the air with an appropriate gauge to check for moisture imbalances. Correct these by adding humidifiers (if the moisture is too low) or de-humidifiers if it is too high. Then, you need to call a plumber and check for and repair leaks near your hardwood floor. At this point, you need to fix the floor itself.

Fixing The Problem

Cupping is a problem that can actually be fixed by sustained and careful sanding. The following procedure will take a few days, but it can be done by just about anybody:

  • Carefully remove all furniture and other items from the room before you begin.
  • Remove the shoe molding around the edges with a pry bar and set it to the side.
  • Place plastic sheeting over the doors to prevent dust and other contaminants from passing through.
  • Sand the floor with 36-grit sandpaper with a hand-held power sander while wearing a dust mask.
  • Once you've finished the entire floor, vacuum and re-sand areas you missed with 40-grit sandpaper.
  • Repeat the above step, but replace the 40-grit with 50-grit and then 80-grit sandpaper
  • Vacuum the floor again, open a window, and coat the floor with a urethane finish.
  • Wait a night for the urethane to dry before sanding with 120-grit paper.
  • Repeat the urethane application process twice, sanding with 150-grit and 180-grit paper after each day.
  • Vacuum the floor and add your last urethane coat.
  • Replace the shoe molding and your furniture after your last coat has dried.

If you don't feel comfortable performing this repair job, call a professional and have them do it for you. They will come in, address the problem, and help you find a solution that will give you the beautiful hardwood flooring that you deserve. Contact a business that sells hardwood flooring for more information.