Plyboo Maintenance Series: How to Prevent Cupping

May 23, 2011 in FAQ series, Maintenance Series

Illustration of a cupped floor. Cupping is the accurate description for this particular type of “warping.”

No one wants a “warped floor,” and with these easy-to-follow tips, your floor will stand the test of time.  Any upward facing warping or bowing of the material is best described in the flooring industry as cupping.  Let me tell you, it’s not a pleasant experience nor is it the sort of thing you’d want to happen to you.  We’ll definitely address several areas in this piece, but first, let’s start simply with:

1. What is cupping?

Image: healingdream /

Cupping is when wood, bamboo, or any other similar timber product takes on a curved shape.  This is most commonly caused by moisture.  The moisture can come from several sources.  Common sources of Moisture include:

  • Uncured concrete subfloors
  • Poor drainage
  • Concrete patch or leveler that hasn’t dried
  • Building leaks, leaks at doors or windows, and leaking appliances
  • Cleaning with water (i.e. wet-mopping)

Although the reason for cupping is moisture related, some floors can cup due to extremely dry conditions.  In this case, it’s helpful to know what’s going on with the relative humidity of your location. Anything under 20% is very dry and humidification is suggested in such conditions.

2. How to Prevent Cupping

Image: joannawnuk /

Try these tools and processes to stop cupping in its tracks:

  • The manufacturer’s installation information
  • Using moisture meters
  • Using moisture testing kits (Such as Calcium Chloride)
  • Administering a complete site inspection and review
  • Allowing all wet materials such as concrete, concrete patch, and concrete leveler to fully cure before installing
  • Reviewing maintenance procedures and avoiding wet mopping the floor
  • Installing the floor last on the project to avoid damage or exposure to water during construction

3. Repairing a Cupped Floor

Image: Patou /

So you’ve found this blog a little too late and want to know how to remedy the situation.  The advice taken from National Wood Flooring Association (NFWA) is to “never attempt to repair a cupped floor until all of the sources of excessive moisture have been [eliminated].”  You will need a moisture meter to perform readings on the subfloor under the affected bamboo, palm, or wooden floor.

If the wood isn’t permanently damaged, the flooring should eventually return to it’s original state.  Keep in mind, that this could take weeks or even months.  If the floor does not return to normal after an entire heating season, it is most likely permanently damaged.  You can sand off the cupped edges on the permanently deformed boards, but first check that they are completely dry.  Take a moisture reading on the flooring itself.  If you find there’s a gradient of 1% or more between the top and the bottom of the boards, they probably haven’t finished drying.

Illustration of a cupped floor after sanding prematurely.  This situation is called “crowning.” Always see that the floor is dry before attempting to sand off the edges.

Information taken from National Wood Flooring Association.