When joints crack after installation what is the cause?
Most cracking in the grout is due to floor deflection or when the grout was too fluid during the installation contributing to shrinkage. These types of cracks are mostly very thin and either directly in the middle of the joint or following one of the sides of the tile.
In most cases, the main cause of cracks is due to the support capacity of the substrate, for inert or moving objects, not exceeding 1/360. The purpose of grout is to absorb this stress and fails if the floor is inadequately structured to meet the industry requirements for ceramic tile.
The Terrazzo, Tile and Marble Association of Canada offers four preferred methods for floor structures in their 2000 - 09300 specification Guide for Ceramic Tile Installation. We recommend reviewing these details to see if the floor conforms to these industry standards.
The most common structural irregularities in floor assembly contributing to cracking are:
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Single layer of plywood;
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Use of weak boards such as Luan, pressed wood etc. as an underlayment;
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Studs spaced further than 16" at the center;
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Using inferior grade plywood (spruce, Pine,
etc.). Only outdoor grade plywood is recommended;
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Narrow space between plywoods (1/4'' should be kept).
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