DIY Hardwood Problems: Causes & Cures

DIY Hardwood Problems: Causes & Cures


What it is: The center of the pieces of flooring appears to be higher than the edges.

Cause: While it is theoretically possible that excessive moisture could cause crowning, it is more likely that the floor cupped and then was sanded flat before it could dry and flatten on its own. When the floor boards did dry to a normal condition, their edges had been removed, making them lower than the center of the board. Gaps are generally formed as the flooring dries.

CURE: First, determine if the moisture content is normal and if all the crowning from the original cupped condition has occurred. After the floor has stabilized, re-sand and finish.


What it is: Cupping occurs across the width of the individual pieces of flooring. The edges are high and the center is lower. It general develops gradually.

• A moisture differential within individual pieces of flooring, usually excessive moisture on the underside of the flooring. More subtle cupping can be caused by lack of proper acclimation (this is general permanent cupping). Potential sources of moisture include: - Building leaks, - Poor drainage, - Plumbing leaks or overflows, - Leaks from dishwashers or refrigerator ice-making units, - Wet or damp basements/crawlspaces, - Concrete subfloors that have not cured, - Plywood subfloors with excessive moisture, - Poor or no ventilation, - HVAC system not operating.
• Flooring also may cup when a wood floor experiences conditions that cause rapid drying on the surface. This condition occurs with gaps as the flooring shrinks.

CURE: Never attempt to repair a cupped floor until all the sources of excessive moisture have been located and eliminated. This can be verified only with a moisture meter that takes readings of the underlying subfloor. As long as the wood is not permanently deformed, or damaged, the flooring will return to its original shape and size when the excessive moisture is removed. This may take weeks, months, or even an entire heating season.

Attempting to sand a cupped floor while it is still too wet may cause subsequent crowning when the floor dries. Flooring that does not return to its original shape, even after completing an entire heating season, probably is permanently deformed. (Taking moisture readings at different levels in the wood flooring also can help determine this – if there is a gradient of 1 percent or more between the top and bottom of the boards, they probably are not done drying.) If the boards are permanently deformed, the cupped edges may be sanded off.

For floors that have cupped due to drying, relative humidity should be increased. Relative humidity below 20 percent is considered very dry for wood flooring, and it is suggested that humidification be provided under such conditions.

Gaps - Normal

What it is: Gaps between strips/planks that appear between individual boards and open and close with changes in humidity.

• Most normal gaps are caused by seasonal fluctuations in relative humidity – the floor expands with high humidity and contracts during periods of low humidity. This type of expansion and contraction is considered to be normal and expected for solid wood floors. In solid 2 ¼-inch floors, gaps may be the thickness of a dime (1/32 inch) or wider. Wider boards have even wider gaps.
• Square-edged floors show gaps more than beveled floors, and light-colored floors show gaps more than dark floors.

CURE: Normal gaps can be minimized by using the HVAC system to control fluctuations in humidity in the building. The use of humidifiers or dehumidifiers can harrow the overall fluctuation range.

Gaps - Abnormal

What it is: Gaps in the floor that remain with seasonal change. If some boards appear glued together by the surface finish (See Sidebonding).

• Edge crush from prior exposure to extreme moisture (especially for solid, flat-grained flooring).
• Hot spots in the subfloor, such as poorly insulated heating ducts, hot water plumbing lines, radiant heating systems, register opening, and refrigerator motors.
• Debris between boards during installation.
• Improper nailing/nail position.
• Flooring installed with an excessively high moisture content or over a subfloor with excessive moisture.
• Flooring not installed tightly together to begin with.
• Foundation settlement.
• Improper subfloor materials that will not hold nails.
• For glue-down floors, early foot traffic, incorrect adhesive, the wrong amount of adhesive transferred or used, the wrong amount of flash time for the adhesive, or not using a roller when recommended.

CURE: Eliminate the cause, then restore normal humidity levels. After the floor has stabilized, use filler in gaps that are small enough to be filled (typically up to 3/32 inch), and recoat the floor. For larger gaps, use a sliver or “Dutchman” to fill in the gap. Pulling up the entire floor and reinstalling may be necessary.

Squeaky Loose Floors

What it is: The floor causes objectionable squeaks or other noises.

• Movement of the wood flooring system, subfloor system or underfloor supports.
• Inadequate or improper nailing.
• Weak subfloor.
• Improper subfloor material.
• Insufficient or incorrect adhesive.
• Floor subjected to excessive moisture or excessively dry conditions.

CURE: Noises in only certain areas may be fixed by injecting adhesive into the problem area, screwing the floor down from below, strengthening the subfloor from below or using facenails or screws and plugs. Squeaks also may be lubricated with graphite, wax, or baby powder, although such solutions will contaminate the floor for future finishing.

Floors that are noise and loose throughout the entire area usually have to be pulled and reinstalled, correcting the problem – whether it is caused by the subfloor; fastening schedule or adhesive.

Floor Sanding Problems





Fisheye:  Murphy Oil soap, Mop & Glow, and citrus-based cleaners can penetrate into previously applied floor finish and act as contaminants when the floor is next recoated.  A complete sanding usually negates this, however, sometimes the contaminants will penetrate into the wood subsurface and can show up not until after coating the newly sanded floor.  Candle wax, oils of any kind, floor paste/wax are all potential culprits.