Gap is not a 4-Letter Word

“Dents du bonheur” is a French phrase for happy teeth, you know, the two front ones that have a gap. In parts of Africa it is a sign of wisdom to have that gap and in Chaucer’s time women with that quirky feature were considered attractive. There are many other things in life that have gaps that aren’t considered bad. Frequently with wood flooring however, this occurrence signifies a problem. The issue isn’t necessarily with the gap itself, but the understanding of what is going on. So here’s a run-down of what makes a normal gap, the type that isn’t a 4 letter word.

Environmental / Seasonal Gaps

What is going on:

Gaps typically show up in the winter when the air is dry and return to normal in the Spring. This happens due to seasonal changes and is normal for most wood floors.

Low relative humidity brought on by naturally dry winter weather combined with firing up the heater causes indoor air to become dry and draw moisture from the wood flooring. For solid wood floors gaps tend to vary in size relative to the width of the boards. Wider plank floors will gap more than their narrower counterpart. Light-colored and square-edge flooring will show gaps more than dark or beveled floors. With engineered products, you may notice the sides curling or the ply backing separating.

Homeowners that keep their house in the 35-55% relative humidity range with an in-home humidifier will help reduce the occurrence of winter-time gaps.

What may happen:

A homeowner may worry because their floor gaps. When this call comes during the dry season, there’s a really good chance that it is due to low moisture content in the wood caused by low relative humidity in the home’s environment.

Start by encouraging them to get a hygrometer and humidifier to help keep the floor stable during seasonal extremes, When spring rolls around, see if the gaps have closed back up.

Infield Expansion Gaps

What is going on:

Some gaps are intentionally included, meaning you need them. Wood flooring is an organic material that expands and contracts… a perfect extension of the natural design of trees. Under certain conditions in the installation process, gaps need to be present so a future problem doesn’t appear.

One of these instances is winter time installation when the wood’s moisture content is at its lowest. This allows for the natural expansion and contraction of boards from summer to winter. The wider the plank, the more critical this infield expansion gap becomes. If this allowance is not made, the boards may cup and cause damage during the summer.

The exception to this rule is with engineered flooring due to the product’s built-in stability.

What may happen:

The floor was installed in the winter when the moisture level of the wood was at its lowest and the air was dry as the Sahara. Two things can happen at this point:. First, the floor is installed and expands in the spring when the air becomes more humid and the floor boards take on moisture.

Or the floor is installed allowing for expansion. This is usually done by installing with a dime, washer, or thin weed- eater line placed between the flooring boards leaving the necessary gap. When summer comes around, the floor can expand without damage.

Manufacturer’s Gaps

What is going on:

The last set of gaps come from the flooring manufacturer’s side of things and is typically seen with a solid product. What happens is that the best lumber is milled first for the top quality grade. What is left goes to lower grades of flooring. It is in these grades of flooring where tolerances are less and gaps may appear during or after install.

This is all well within industry tolerances for that grade of flooring. Trowelable filler may be applied in the sand and finish process to fill in the gaps, or could be left unfilled for a more rustic appearance.

What may happen:

A couple years after installation a homeowner may call saying gaps have recently shown up in their flooring. Remember the filler? As the floor goes through seasonal expansion and contraction cycles, some of the wood filler may work itself out of the gap.

As the floor is swept, vacuumed, and cleaned, small parts of the wood filler may be removed. Eventually there isn’t filler left and so the gap appears. At this point wood putty can be used to replace the filler and get the floor looking like it originally did.