One summer afternoon you come down to lunch and you suddenly notice something is not quite right. When your sports magazine slips from your grasp and you bend to pick it up from the floor, you discover what it is. The smooth glossy hardwood surface seems somewhat uneven, dipping slightly in places. What is it and what could have caused it? Can it be fixed and how?

In this article, we shall be examining all these questions in detail and providing answers to each of them to enable you to resolve the problem as efficiently as possible and restore your floors to their initial state.

What Is Cupping in Hardwood Floors?

Cupping in hardwood floors refers to a condition that causes individual planks to rise at the sides. It may be considered to be the opposite of crowning where the center of a plank rises higher than the edges.

In both cases, your floor will lose its even smoothness resulting in its surface becoming irregular. However, in the case of cupping, its planks will take on a concave or cup-like shape hence the name of the condition.

Cupping in wood floors

Causes of Hardwood Floor Cupping

The main cause of cupping in hardwood floors is the presence of excess moisture in the immediate vicinity.

The material from which hardwood floors are made is especially susceptible to moisture due to the tendency of wood to absorb it, particularly when it is present in large quantities to adjust its own moisture levels to match those of its surroundings.

Cupping affects both engineered and solid hardwood and can occur under the following conditions:

  • Spills: If spills are not cleaned instantly or properly, the fluid will seep into the wood resulting in its swelling and the alteration of its form.
  • Leaks: Because leaks often take a while to detect, they can be especially damaging to hardwood floors due to the prolonged exposure to moisture they cause.
  • Excess subfloor moisture: If your basement or crawl space happens to be affected by dampness, it may cause cupping in the floorboards in the room above.
  • Changes in weather conditions: Certain climates experience rather warm and humid summers and the season can result in elevated levels of moisture and with it the risk of cupping.
  • Improper installation of flooring: Hardwood flooring must be given time to adjust to surrounding moisture levels by means of a process known as acclimating or conditioning, before it is installed. Failure to take this step could result in cupping in a matter of months.

How to Fix Cupping in Hardwood Floors 

It is possible to fix cupping in hardwood floors by taking the following steps:

Ascertaining Moisture Levels

This should be the first step you take before attempting to repair or replace all or part of your flooring or before seeking professional assistance.

This can be done by using a wood moisture meter to check moisture levels in every part of your home.

Conducting due diligence in this regard will enable you to determine moisture levels and their source, and play a key role in enabling you to determine the next step.

Address the Source of the Moisture

Common causes of excess moisture in your home include:

  • Leaking pipes: If the cause of the problem happens to be leaking pipes, you will need to have them repaired.
  • A leaking dishwasher: In the case of this appliance you may need to take a look at its float switch, its gasket, the hoses, the valves, or the door latch. It may even be a matter of using the correct dishwasher detergent or simply ensuring it sits level.
  • A leaking fridge: This may be due to the blockage of the defrost drain or the uneven placing of the appliance. However, if neither of these issues happen to be the cause, professional assistance may be required to resolve the leakages.
  • A damp crawl space:  This may be resolved by placing a vapor barrier to prevent moisture from filling your crawl space. However, you may need to call on the services of a water mitigation professional.

Regulate the Moisture Content of Your Home

This step can be especially effective if the cause of cupping is due to seasonal changes at different times of the year.

You will simply need to use a dehumidifier to eliminate the excess moisture in the air and restore conditions to optimal levels.  Depending on the level of moisture damage in this case and the promptness with which action is taken, you may see your floorboards return to normal.

Related Reading: How To Repair Water-Damaged Hardwood Floors

If the cupping is not reversed once you have taken this step, you may need to proceed to replacing your floor or sanding it.

In either case, you will have the option of relying on professional assistance or replacing or sanding your floor yourself.

Should You Sand Down Cupped Hardwood Floors?

major cupping in wood floors

You can do so. However, you will need to ensure you have carried out the steps enumerated above with regards to ascertaining moisture levels, addressing the cause of the moisture, and regulating its levels in your home. You will also need to ensure that your hardwood floor and the subfloor are both completely dry — a state which can take a long time for both to attain.

Failing to do so could result in the wooden planks curving upwards at their centers (crowning) when it does dry out eventually.

To repair your hardwood floor by sanding when you are certain of complete dryness and are certain that the cupping is permanent, you will need to obtain the following items and implement the steps described below:

  • Sandpaper in four grades (36-, 40-, 50- and 80-grit)
  • Floor sander
  • Orbital sander
  • Plastic sheeting
  • Tape
  • Ear protection
  • Dust mask
  • Microfiber mop
  • Hardwood floor cleaner
  • Soft-bristled broom or brush
  • Vacuum cleaner
  • Floor stain
  • Floor finish

1. Emptying the Room

Sanding involves minute dust particles being released in immense quantities into the air, and they may permeate your curtains, rugs, or upholstery if they are left in the room. Besides, you will need to have access to the entire section of the floor which is affected by cupping, and any furniture present may prevent you from being able to do so.

2. Preparing the Room

Once the room has been emptied, you will need to seal every entrance and aperture with tape and plastic sheeting.

You will also need to remove the shoe molding to ensure you are able to get to every part of your floor.

Because it is important to have a clean surface when sanding, you will need to sweep the floor and mop it as well with a microfiber mop.

3. Starting the Sanding Process 

You will need to wear your dust mask and your ear protection before you start.  Next, you will need to start sanding with the roughest grade of sandpaper out of the four (36-grit) since it is the best for leveling the wood.

Here it is important to follow the grain of the floor since failing to do so can actually result in considerably more wood than necessary being removed.

Any tight spots which cannot be accessed by the floor sander will need to be tackled with an orbital sander using sandpaper of a slightly higher grade (about 40-grit).

Once you have covered the room in its entirety, you will need to vacuum the floor. 

4. Changing to a Higher Grade of Sandpaper

This step involves sanding the surface with sandpaper of a slightly higher grade to ensure you completely level any elevation due to the curving of the hardwood.

You will need to replace the 36-grit and 40-grit sandpapers on the floor and orbital sanders with 50-grit sandpaper.

At the end of this step, you will need to vacuum the floor as for the first step.

5. Changing to Your Highest Grade of Sandpaper

During this phase of the sanding process, you will need to replace the 50-grit sandpaper on both sanders with 80-grit to ensure your floor is smooth enough for you to apply the finish to it.

As with the previous two steps you will also need to vacuum once you are done.

6. Applying the Finish

You will need to thoroughly ventilate the room, by taking down the sheeting from the windows and doors. Next, you will need to slightly dampen a microfiber cloth and clean the floor against the grain and then wait for the floor to dry completely.  

You will then be able to stain the floor to your preferred color and then apply the finishing to it following which you will need to leave it to dry — a process that may take a day or even up to a week.

It is worth noting that sanding can be rather labor-intensive and many people prefer to hire the services of a professional to carry it out.

Will Cupped Hardwood Floors Flatten Out Over Time?

Depending on the extent of the damage, and the promptness with which the exposure to the excess moisture is stopped, your cupped hardwood floors may flatten eventually.  

It is worth noting that they can take a considerable length of time to do so and as noted above, repairs or sanding should only be carried out once you are certain that cupping is permanent.

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