When either the whole or portions of the flooring have become separated from the sub-floor, they form a bridge. This is often accompanied by various degrees of cupping. Buckling is a much rarer occurrence. This is when the flooring lifts from the sub-floor, reaching several millimetres in more extreme cases. The reaction to excessive moisture is the reason why this may occur.
Bridging and buckling are caused by the expansion of the flooring due to a rise in moisture content. When the flooring meets obstructions, such as walls and door frames for example, the horizontal movement of the floor is obstructed and expansion causes lifting.
Bridging and buckling are usually an indication of high levels of moisture. However, cumulative expansion can cause bridging and buckling from normal seasonal expansion when the floor has inadequate expansion especially in large floors.
Even where expansion gaps are present around the perimeter of the flooring and obstructions, excessive expansion can cause buckling within the main body of the floor.
If wood flooring is installed direct to an existing wooden base and where the existing wooden flooring is bonded to a direct finish concrete slab which does not have a DPM, once the wooden flooring is covered over, moisture can no longer escape the existing wooden flooring. The moisture content of the existing wooden sub-floor rises and expands, pushing up the new flooring.
Bridging and buckling also represent a trip hazard which must be considered if natural drying is intended to play a role in the correction of the problem.
Find and remove the source of the moisture problem if one exists
Where flooring is fitted by nail or adhesive fixing, bridging occurs where the fixing to the sub-floor has broken away. Spot repair / replacement or re-installation may be adequate in minor cases, whilst complete re-installation or replacement is sometimes required due to the fact that the floor has often shifted from the sub-floor throughout the area. Even where flooring appears flat, fixings may be compromised due to cumulative horizontal movement.
If floated floors have bridged because of inadequate provision of expansion, the problem can often be remedied. This is because the performance of floated floors is not dependent on fixings to the sub-floor which can affect bridged / buckled floors. Integrity of the tongue and grooves can however sometimes be affected by buckling, and to a lesser extend by bridging.
When sanding and finishing existing floors during the season of low humidity, consider the possibility that small gaps between flooring elements are needed for expansion during the season of high humidity consequently it is sometimes inadvisable to fill gaps between these elements . This is especially significant in large floor areas.