Gaps occur when the wood loses moisture and the boards shrink, this is more prone to wider boards. Some gaps are normal and appear seasonally during periods of low humidity- usually in the winter.
If you have recently noticed the gaps or if they appear to be worsening, check the humidity level in the home, this should be similar to the humidity levels outside.
Wide plank solid flooring can have seasonal gaps between the boards up to 6mm. Light coloured flooring and square edged floors also tend to show gaps more than dark, beveled edge flooring. Also make sure you regularly measure the indoor climate, relative humidity should fall between 30 and 50 percent and the temperature should be between 60 and 80 degrees fahrenheit year round. Normal gaps will disappear once conditions return to normal.
Abnormal gaps are more severe and they remain in the floor after seasonal fluctuations in humidity. Abnormal gaps can occur for a variety of reasons, including having excesive moisture in the subfloor or flooring during installation that later dries out or using an improper nailing schedual.
In order to fix the problem, the cause of the gaps needs to be remedied.
Check that the indoor humidity levels are within the normal range and the source of exessive moisture has been eliminated. Small gaps can be filled with wood filler and refinished. Large gaps can be repaired with a sliver of matching wood between the gaps, followed by a sand recoat of finishing product. If the gaps are extensive and dont change with increased humidity levels, the only option is to replace the floor.
Preventing abnormal gaps in the floor involves a thorough check of the flooring and the job site before installation. Check that there are no sources of excessive moisture and take several moisture readings of the subfloor and make sure the wood has been properly acclimated. For solid strip flooring, the moisture content of the wood and subfloor should be within 4 percentage points of each other. Know what the average moisture content is in your area and make sure the wood maintains that average moisture content during seaonal extremes of high and low relative humidity. Also check for sources of hot spots in the subfloor such as poorly insulated hot water pipes and radiant heat systems. Make sure you use the correct vapour barriers on subfloors.
The opposite of gaps, cupping is caused by the flooring gaining moisture and expanding, creating raised edges and lower centres on the boards. Similar to gaps it is caused by excessive moisture, usually in the subfloor. Appliance leaks, seepage from outside, wet cellars, wet basements, poor ventilation and improper istallation techniques are other possible causes of cupped floors.
In many cases a cupped floor will flatten out once moisture levels have returned to normal. This could take weeks or even months for the floors to flatten. In servere cases resanding the floor will correct the problem. Before attempting to resand, be sure that the source of the moisture has been removed and that the cupping is a permanent condition. If you sand a cupped floor flat before it has completerley dried, it will crown and create yet more problems. Take several moisture readings on and around the floor and at different depths in the boards, if there is more than 1% moisture difference between the bottom and the surface of the boards, the floor probably needs further drying.
Following proper installation methods for the product and your area helps prevent cupping. Make sure the job site conditions are ready for installation, make sure all wet trades are out and lastly make sure the subfloor is at an acceptable moisture content- prevents problems later. If you live in an area that has fluctuations in temperature and humidity, its even more critical that the job ste conditions are normal for the area.