Why Tile and Grout Crack

By Brian Hansen, Project Manager | December 25, 2019

Why do tile and grout crack?  It is easier to understand why a material fails if we first understand how it is made.

Tile is clay formed into a desired shape then treated with fire to harden it. The firing process turns the malleable clay into a solid material that is very hard and very durable but intolerant of movement.

Grout is usually a powder that the installer adds water to.  Typically, a well-mixed grout looks a bit like dark-gray cake-frosting.  The grout serves the dual role of adhering the tile to the substrate and filling the seams between the tiles.

Tile Installation 101: Grout is applied to an appropriate substrate with a trowel and, before it dries, the tiles are installed onto the soft grout.  As the grout dries, it forms a bond between the tile and the substrate.  When installed properly, these materials can last for centuries.  When installed improperly, they generally fail within a few years.  This often ends with expensive, repairs that could have been avoidable.

Masonry products like tile and grout are very rigid and brittle.  Once they have cured, they cannot tolerate a lot of movement. If they do, their brittle characteristics will lead to cracking. To obtain a low tolerance for movement, the
installer must carefully consider the substrate the tile and grout will be fastened to. The ideal substrate is a stable and

rigid cement-based material in good condition.  However, in the real world of construction projects, the substrate is often something a lot more flexible than solid cement (ex: plywood).  A plywood substrate represents the added disadvantage of a flexible organic substrate prone to expand and contract with changes in humidity and temperature.  We do not recommend adhering mortar directly to plywood.

A substrate that is more flexible than the grout can be used, but only with very careful planning to ensure the tile and grout stay put.  Examples of careful planning include choosing appropriate grout additives for flexibility, expansion joints, and manufacture-recommended trim features that allow movement.  Without proper planning to accommodate the movement of a substrate below tile and grout; the tile will respond by fracturing.  Those tiny fractures allow water to penetrate and further deteriorate the surfaces below and behind the tile and grout.  This is especially injurious over a few freeze-thaw cycles on building exteriors.  The water relentlessly works its way into the fractures then freezes.  The ice expands and breaks the nearby grout causing more fractures letting in more water and making the original problem much worse.

Most of the tile and grout failures we see at Team Engineering are caused by th

e installer placing the materials over an incompatible substrate.  If you are considering installing tile but don’t know the first step, we recommend finding a tile you like then referring to the manufacturer’s installation instructions.  This can be easily found online or in your local home improvement store.  The next step is to verify that the substrate is in good condition.  If the substrate is damaged by water and/or wear, replace it so there is a stable surface to adhere the tiles to.

Finally, tile and grout are filled with very small pores that can easily absorb water.  Therefore it is always worth it to seal the tiles and grout so they can resist water infiltration and the fractures that accompany them, especially if they might be exposed to extreme temperatures or moisture.

If you have questions about tile installations or if you are planning a remodeling project, call us today and we will help plan a successful project that you will enjoy for a very long time.

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