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Hardwood Floor Cupping: What Is It and How Can You Fix It?

Hardwood Floor Cupping

Cupping in hardwood floors is a common issue that happens due to changes in moisture levels. This can be caused by either a decrease in the relative humidity above the floor or an increase in moisture from below. 

While minor cupping is a natural reaction to moisture and usually isn’t a cause for concern, severe cupping can point to a serious moisture imbalance. Understanding the causes and solutions for cupping can help both professionals and homeowners maintain the beauty and integrity of their hardwood floors.

What is hardwood floor cupping?

When moisture interacts with hardwood floors, the side of the boards closest to the moisture expands. This can result in: 

  • Cupping, where the center of the board is lower than the edges
  • Or crowning, where the center of the board is higher than the edges

In the early stages, cupping can be noticed when light from a window reflects onto the floor, creating small shadows where the edges of each floorboard are slightly higher than the middle.

What are the causes of hardwood floor cupping?

Understanding the reasons for which cupping happens is essential for addressing and preventing the problem. 

The root cause is moisture, as wood is a porous material that easily absorbs water. This is true for both hardwood and engineered wood flooring, although the plywood core of engineered hardwood is more resistant to changes in internal moisture content. Even with his endurance, engineered hardwood can still end up cupping. 

By pinpointing the sources of moisture, you can take steps to protect your flooring.

1. Improper installation

Some causes of floor cupping can be traced back to the original installation. Properly preparing the subfloor is essential for durable, functional hardwood floors. Installing wood flooring over a damp subfloor can lead to moisture-related issues later on. That’s why you might want to learn more about ventilation for hardwood floors, vents, and dampers

And make sure your floorboards have a stable internal moisture content that will last. For example, when you install and use air conditioning, the room’s humidity levels will change, affecting the moisture content of your wood floors. Lay down your floorboards only when the room’s moisture levels are stable.

2. Humidity levels

Humidity plays a great role in the maintenance of hardwood floors. Wood naturally adjusts its internal moisture content to match the moisture content of the surrounding air. In high humidity, wood floors absorb more moisture, causing them to expand and cup. Contrarily, low humidity causes floors to dry out and shrink. 

These humidity levels typically fluctuate with the seasons, especially in regions with humid summers and dry winters. Fortunately, cupping caused by humidity is often less severe and may correct itself when the season changes.

3. Spills and leaks

Water damage is a common risk wherever there are leaks or spills. So protecting your hardwood floors from spills is an essential part of their maintenance. Clean up spills promptly, make sure the area dries completely, and pay special attention to mudrooms and entryways, which can accumulate water as people enter on wet days. 

Unfortunately, you may not spot every water stain right away. Areas around sinks, dishwashers, and other water-based appliances are particularly vulnerable. Leaks can also occur beneath the surface, around pipes, and other plumbing components. 

If you notice cupping in your floors without an obvious source, there may be significant water damage in your home. This can lead to mold and other issues beyond your flooring, so it’s very important to locate and address the problem as soon as possible.

4. Subfloor moisture

Another common cause of floor cupping is moisture entering through the subfloor. This is especially predominant in homes with basements or crawl spaces that are more humid than the rest of the house. Water damage in the subfloor, often due to leaky pipes or similar issues, can also lead to moisture seeping into the floorboards from below. 

Since the subfloor is a critical part of your flooring system, it’s important to prepare it properly before installing hardwood floors. This involves thoroughly cleaning and drying the subfloor to eliminate moisture issues before laying down the first planks.

How to assess hardwood floor cupping

There are 2 situations: hardwood floor cupping for moisture issues or for drying issues. 

  1. In the first case, test the moisture on both the underside and topside of the flooring. This way, you will determine if there really is an imbalance. If the underside shows a higher moisture level, the source is likely the subfloor. Consider whether the flooring was too dry when installed for the expected natural ambient conditions. If there is a cavity beneath the subfloor, test the humidity within it. Excessive humidity in this cavity could indicate blocked ventilation or air bricks.
  2. In the second case, check the atmospheric humidity level. If it’s below 35% RH (relative humidity), the conditions might be too dry. Look out for potential heat sources that could dry out the flooring, such as strong sunlight from skylights or large windows, hot water pipes, or underfloor heating systems.

How to fix hardwood floor cupping

If you find cupping in your home, the first step is to identify the source of the problem. That’s because just drying out the floor without addressing the underlying issue won’t solve the long-term problem. To fix it, you need to eradicate the source of the water damage. Once that is done, you can work on restoring your wood floors to their original beauty.

  • For minor cupping, the solution might be as simple as using a dehumidifier to return the room to its normal humidity levels. 
  • However, for more significant damage, the consequences can be more severe. Besides the visible warping of the hardwood floorboards,  cupping can worsen and create gaps between the boards. When the relative humidity drops, the boards may not return to their original shape and can buckle away from the subfloor or even splinter and crack. The floor could even entirely fail. In such cases, investing in a professional drying treatment can help return your floorboards to their normal shape.

How to prevent hardwood floor cupping

Here are a few tips to help you prevent hardwood floor cupping if you are having floors installed:

1. Allow the wood to acclimate to the home’s normal living conditions before installation.

2. Ensure that installers are using a proper moisture barrier on the subfloor.

3. Regularly monitor the moisture levels in the home.

4. Clean up spills on floors immediately and avoid wet mopping wood floors.

5. Never sand down a cupping floor. Wait until the moisture issue is resolved; then, if necessary, the floors can be sanded. Sanding before solving the moisture issue can cause the floors to develop a convex shape once the moisture dissipates.

Still struggling with hardwood floor cupping? Reach out to First Atlanta Flooring! Our team of experts is here to guide you with advice and top-notch products and techniques.