Wet Hardwood Floor Cupping

Underlayment and or subfloor that is too wet at the time of installation will cause wood floor cupping.

Wet hardwood floor cupping.

When moisture interacts with a hardwood floor the side of the boards closest to the moisture expands. The simplest way to think of wood floor cupping is to imagine the edges of each plank sticking up higher than the centers. The general effect is easy to demonstrate by putting a small strip of paper onto a small drop of water. A cupped floor develops as moisture from the underlayment or subfloor moves upward through the hardwood as the back of the wood becomes wetter than the face of the wood.

It ends up looking a little like an accordion. Cupping in solid wood floors cupping occurs in solid wood flooring as a result of an elevated mc in the bottom of the flooring compared with the mc of the face. If you imagine a picture of a child drawing a boat in the water then the water will give you a good idea of what a cupped floor looks like. Wood is hygroscopic in nature and thereby tends to absorb moisture from its surroundings causing problems in hardwood floors.

The paper will curl up away from the water. This expansion can be in the form of cupping the center of the board is lower than the edges or crowning the center of the board is higher than the edges.