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Flooring - Finished Flooring

Cracking Of Hardwood Joints

Problem: Cracking Of Hardwood Flooring Joints


Hardwood swells or shrinks after installation.

Cracks that develop within weeks or months of the installation of a well laid hardwood floor are usually the result of changes in moisture content.

As moisture is absorbed by the hardwood, it expands, pressing neighboring boards against one another. This pressure crushes the wood fibers, leaving what is known as compression set. After the hardwood has been compressed in this way, it never completely recovers its original width. When hardwood loses this accumulated moisture, each board shrinks away form the other, leaving cracks that are equal to the amount of crushing or set the board underwent as shown in Figure 33.

Compression cracks in hardwood flooring
Figure 33 - Compression cracks in hardwood flooring


If hardwood is dried excessively, it can shrink from its original width and cause similar gaps without the crushing taking place. Once again, cracks can develop between the boards:

Use a moisture barrier under the hardwood:

  • Wood flooring should be separated from sources of high moisture by a moisture barrier. This is particularly important over areas such as crawl spaces. Installation of polyethylene over the sub-floor prior to installation may prove helpful, and the installation of a ground cover is essential.
  • If the wood flooring is installed over a source of heat, such as a furnace or non-insulated heating duct, it may dry out and thus shrink. Install insulation above such sources of heat to prevent over-drying of the hardwood floor above.