Clumping and Edge bonding
Clumping is a term used where the boards have gapped unevenly across the floor. Rather than having a small gap between each board, there will be a group of boards without gaps between them, then a large gap and then another group of tight boards. The problem is initially caused by a reduction in the moisture content of the boards, which is exacerbated by the coating system bonding the boards together and thus not allowing the boards to separate.
The finish seeps between the boards on initial application, and on drying securely glues the boards together. The forces involved in the shrinkage will then open up a large gap every 4-6 board widths. In some cases, the bond may be stronger than a particular board, which might split the board. The problem of the clumping cannot be resolved, the edge bond, once established is permanent. Many of the manufacturers of coating systems which have this gluing effect, have developed a product which is applied over the boards before the first coat of finish is applied to effectively act as a bond breaker. The changes in service conditions and inspection requirements are as per gapped boards.