Guide to Wood Floor Damage Types, Diagnosis, Repair
InspectAPedia^®  -    

• Catalog of types of damage to different wood floor materials
• Description of repair approaches for damaged wood floors
• Buckled wood flooring
• Cupped wood floorboards, convex & concave floor cupping
• Gaps between floor boards or parquet flooring - cause/cure
• Rotted wood flooring
• Scratched wood flooring
• Stained wood flooring

This 1940's wood floor buckled severely because of wet conditions in a gymnasium after the roof leaked.

But even if a building is not subjected to flooding or wet floors, if the wood floor was installed without adequate clearance around its perimeter buckling can occur when moisture increases in the building.

Very large wood floors (such as in this gym) may need an inch or even more of side clearance at the building walls - a detail accomplished by building out floor/wall baseboard trim if necessary, or in the case of newer products, by the combination of clearance gaps and a floating floor design.

Compare our photo at left of concave (curved down) cupped wooden floorboards with the convex (curved up) cupped floor boards in the photo at the top of this page.

At left you can easily see the concave cupping of the floor at left by looking at our flashlight beam across boards in the upper portion of the photo. (The center of concave cupping is down and edges of concave-cupped floor boards are raised - think of "cave" as "caving in" if you want to remember this distinction.)

Diagnosing why a wooden floor has become cupped is an important step in correcting the problem, since we need to identify and correct the moisture source.

There are exceptions, but in general a board swells on its side that is most moist. So on an interior floor like the one shown at left, the fact that the center of the floorboards is cupped "down" we infer that it is the down-side of these boards that is more moist than the finish side facing the room. We find this condition in homes with finished wood flooring installed over a damp or wet basement or crawl space.

At our page top photo the finish floor boards seem to be cupped "up" - suggesting that this floor has been wet from above.

If the floor board cupping is minor and hard to see, you might decide to just address the moisture problem and leave the floor alone. It won't recover, but it the floor should not get worse. How would we repair a badly cupped wooden floor? Sanding the floor flat is an option unless the boards have not only cupped but come loose from the subfloor. In that case floor replacement may be necessary.

Gaps between wood floorboards may occur for several reasons, but the common underlying cause is a moisture problem.

Installing wood flooring before it has had an opportunity to acclimate to the indoor moisture level of its new home often means that too-moist flooring was nailed in place, later shrinking as building heat further dries the wood.

The gap between the flooring shown at left is viewed from the under-side of the floor of an older building. This is a ship-lap joint whose boards have separated about 3/16".

Gaps can also appear between sections of a wood parquet floor, as shown in our photo (left).

Do not rush to fill in gaps like this in wooden floors. Particularly in the case of wideboard flooring the width of individual boards increases and decreases seasonally as building indoor moisture levels increase (typically in the summer) or decrease (typically in winter).

If you fill the gap between floor boards in the dry (wide gap) season, when the building moisture increases and boards swell the swelling floor boards will push against the gap filling material, actually crushing the edges of the floor board.

Then when the building dries out again a new gap will appear. Or in extreme cases the floor may buckle in damp weather. In either case, it's better to just vacuum out the dust and debris and leave these wideboard floor gaps alone.

At Wood Floor Types where we illustrate a restored and re-finished wide-board floor in an 1860's home, if you click and enlarge the photo you'll see that we left the flooring gaps open. In fact during restoration we sometimes have to pick out putty or other stupid crack fillers that someone has applied earlier.

A common complaint we've investigated is shrinkage gaps in wood flooring installed over radiant heat tubing. The underlying cause may be flooring that was too moist at installation (see above), or operating the heat at a higher than recommended temperature.

In the gapped wood floor over radiant tubing shown here, the owner, attempting to eliminate a smell associated with the radiant heat tubing, ran the heating system at high temperature, perhaps contributing to this floor gap problem.

Also see RADIANT HEAT Floor Mistakes to Avoid where we illustrate a costly and incompetent radiant heat installation below ceramic tile on slab on grade.

Pet urine stains on wood floors - pet stains can ruin wood flooring. Stains are deep enough into the wood that almost no amount of sanding will remove them.

We have had some wood floor stain removal success by careful, by-hand bleaching combined with sanding, followed by careful blending of hand-mixed wood stain products to return the color of the wood floor section to that of its neighbors. See Black Flooring Stains from Animals for details.

Nail & moisture stains on wood floors - Where small black stains developed in a wood floor in a 1920's bungalow that we restored (our lab and office) we had great success by combining sanding with spot bleach using a Q-tip to lighten the black spots where in prior years moisture had caused bleed and corrosion staining around those fasteners.

Any exposed nails were set into the flooring before sanding. After sanding we sat with a q-tip and a damp cloth, dabbing and bleaching black spots, wiping and washing off the bleach when the stain was light enough - thus avoiding over-bleaching the floor. We mixed wood stain products to bring the color of the stained-bleached spots back to the surrounding flooring.

Here is a long strip solid oak wood floor that's shows ugly but fairly superficial scratches. To make this 1970's strip oak wood floor look perfect, sanding and re-finishing may be necessary.

But an alternative to try first is thorough cleaning, perhaps buffing with steel wool, followed by application of a sealant and finish coating. Often superficial scratches in a wood floor disappear from view when the scratched finish coating is restored.

It's usually a better practice to repair a floor with the least aggressive means possible, preserving the material for a longer life.

Contact Daniel Friedman for website content suggestions or for fee-paid consulting