Once installed, hardwood planks naturally react to changes in the atmosphere which can cause very slight contractions or expansions if properly maintained. This is usual in wood floors due to their moisture absorption properties. However, if planks show signs of cupping or crowning, this indicates a moisture problem and should be tended to immediately to prevent long-lasting damage. In Part 1 of this topic, we will look at cupping and crowning in more detail and what causes it.

What is cupping?

Instead of a floor being level, planks that are affected by cupping will be concave in appearance. It will look like the edges of the board have pushed upwards, causing a slight dip in the middle of the board.

What are the causes?

Excessive moisture beneath the flooring is the main cause of cupping. This moisture is absorbed by the wood on the bottom side of the planks, causing an imbalance. As there is more moisture beneath than on top, this causes boards to swell and force upwards. The dip in the middle occurs due to the bottom of the plank expanding, the top sinking inwards and the sides swelling around it.

Some causes of excessive moisture include a broken waterline beneath the floor, wet mopping causing water to seep through the planks, wrong insulation installed under the floor boards or too much dry air above boards causing that imbalance.

What is crowning?

Opposite to cupping, boards that are a result of crowning have a convex appearance where the middle of the plank is raised higher than the edges. This arch shape sticks out of the floor causing a bump.

What are the causes?

Again, an imbalance of moisture is the main cause of cupping, however this time there are higher levels of moisture on top of the boards compared to underneath. It is more common to see during warmer climates as the relative humidity inside is higher than in colder months. This causes the wood to absorb the excess moisture which can lead to planks swelling.

Other causes of crowning can include prolonged moisture on the surface (e.g. mopping), water leaks from appliances such as a fridge/dishwasher or spills that have been left unattended and not wiped immediately. The latter can even include things like underneath a pet’s water bowl.

The main thing to remember with cupping and crowning is that they occur due to an imbalance of moisture on either the underside or top of the flooring. In Part 2, we will be looking at solutions to fix them, followed by preventative measures you can take in the future.