Cracks in the Foundation and Ceramic Tile

Rules of Concrete

• Concrete foundation cracks are generally caused by one of two things. When cement cures it shrinks, with the estimate being one-quarter inch for every 100 linear feet of concrete poured. The second is when the slab expands in the warm months and contracts in the cool months. Little spiderweb cracks throughout the concrete are of no concern, although large expansion joints for movement will need to be addressed.

Expansion Joints

• Expansion joints are either cut into the concrete after it has set up, or they are built into the foundation when it is poured. Quarter-inch expansion joints are normal for any expanse of 100 feet to allow the concrete room to breathe and move and shift over the years. This joint needs to carry up through the tile installation, with a caulk joint along the top of the expansion joint rather than grout filled as the rest of the joints.

Basic Materials for Tile

• Spiderweb cracks are normal in any concrete installation, and protecting against them is as simple as using the proper installation materials for tile. Latex-modified thinsets and grouts are a requirement as they provide the elasticity that the tile installation needs to absorb the seasonal movement of the concrete foundation over time. You can also add more liquid latex to your thinset and grout if you think you need extra protection.

Add-on Protection

• Extra protection comes in the form of various anti-fracture protocols. You can use a paint-on waterproofing and anti-fracture membrane for one of the easiest methods, or you can install a tar-backed fiber membrane that works to help with the expansion of the concrete. You can also use interlocking membrane systems that are installed on top of the slab as a substrate for the tile. All of these are designed to take the movement from the slab and keep it contained rather than transferred up to the tile.