Cupping and Crowning in Wood Floors Part 2

Because solid timber floors are a natural product, they react to atmospheric changes more than engineered floors. This means that indoor temperatures and humidity need to be closely monitored to prevent planks from warping in response to moisture in the air. This is known as cupping (when the plank has a concave appearance) or crowning (when the plank has a convex appearance). In Part 1, we looked at cupping and crowning in more detail and what causes floors to react in this way. Part 2 will focus on solutions to fix boards that have been affected, followed by preventative measures.


Solutions for Cupping

Before you dive into fixing the problem, you must first pinpoint what is causing the excessive moisture under the floor and balance it with the moisture levels on the surface. Cupping will continue if the moisture imbalance is not addressed. As soon as you have addressed the problem and balanced out the moisture levels, allow the floor to re-acclimate before conducting any further actions. If planks still show signs of cupping after this equalization process, you can sand and refinish the floor to even-out the surface.


Solutions for Crowning

Follow the same steps for cupping by identifying the cause of the excessive moisture levels on the surface of the floor. Locate the affected area and allow to dry and re-acclimate before sanding down if necessary. If there is severe water damage, it may be too extensive to repair. To prevent this, always address the problem as soon as possible. If caught early, equalization will often solve the cupping problem with no remedial action needed.


Prevention Methods

The main way to prevent cupping and crowning is to keep the atmospheric levels indoor at a consistent level, adapting to seasonal changes where necessary. Wood floors naturally shrink in the winter and expand in the summer due to air temperature changes. A good way to monitor this is by installing a humidifier or dehumidifier to keep humidity levels constant.

Avoid any water having direct contact with the floor surface – solid wood floors are not waterproof and any water absorption can lead to cupping or crowning. Clean spills immediately and don’t use a wet mop to wipe floor boards. Place mats under areas that are susceptible to water spills such as underneath a pet bowl or next to the sink.


If you notice cupping and crowning in your wood floor, try these solutions to fix the problem. You should then follow this prevention advice to keep moisture levels balanced and floors at a smooth level.

Cupping and Crowning in Wood Planks Part 1

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.