Ceramic Tile Problems on Concrete

Structural Stability

• Unstable concrete substrates cause tiles to shift or break and grout lines to crack. Indications of instability include multiple cracks, wide cracks and uneven surfaces. Before laying ceramic tile over concrete, installers should inspect concrete surfaces for damage. Wide cracks and uneven surfaces tend to worsen over time. Unfortunately, concrete surfaces that exhibit severe instability require replacement or significant renovation. However, thin cracks, called "hairline cracks" do not necessarily indicate severe damage. Repair mortar or flexible fillers can repair tiny cracks and holes and prepare a concrete surface for tile installation.

Seepage

• The term "seepage" refers to the transfer of water through a concrete surface. Both concrete walls and floors have seepage, particularly basement walls and ground-contact slabs. The presence of efflorescence, a scaly white coating, indicates seepage. Continuous seepage prevents mortar, tile and grout from properly adhering to a concrete surface. Although etching temporarily removes surface damage and efflorescence, builders must renovate slab or wall drainage systems to fully prevent adhesion problems.

Contamination

• Contaminated concrete surfaces prevent mortar adhesion. Contamination not only refers to dirt and dust but also to grease and oil stains and existing surface coatings. While normal cleaning supplies sufficiently remove dirt and debris from a concrete surface, removing grease and oil often requires heavy-duty solvents. Additionally, tile installers must fully remove existing paints and primers from concrete before installing tile. Ceramic tile mortar must directly contact the concrete; existing surface coatings prevent proper contact.

Solutions

• The common solution to severely unstable concrete surfaces is extensive renovation, such as resurfacing or replacement. To address seepage or moisture problems, builders begin by testing the concrete's surface. To test for seepage, builders can securely tape a piece of aluminum foil to the concrete surface and leave the foil for several days. If condensation occurs on the inside of the foil, the concrete surface has seepage. If moisture occurs on the outside of the foil, the room has interior condensation. Finally, etching and paint stripping compounds help remove severe surface contamination, such as grease, oil and paint.