Tiling Myths That Lead to Wonky, Water-Damaged Results

Cement grout is inherently porous regardless of where it's installed. In dry areas, unsealed grout absorbs cooking oils, dirt, and cleaning product residue, leading to permanent staining. In wet areas, the consequences are more severe: moisture penetrates behind the tile, feeding mold and degrading the substrate. Apply a penetrating grout sealer to all cement-based grout after it has fully cured, typically 48–72 hours after application, and reapply every one to three years depending on traffic and exposure.

Grout joint width isn't merely aesthetic — it accommodates minor tile size variation (known as calibration tolerance) and allows for the slight movement that occurs as buildings settle and temperatures change. Without spacers, cumulative drift adds up quickly, so by the time you reach the far wall, your lines may be visibly skewed. Spacers come in sizes from 1/16 inch to 1/2 inch; the correct size depends on tile type and the look you're after. Rectified tiles (precision-cut to uniform size) can use narrower joints; natural stone and handmade tiles typically require wider ones.

Proper mortar coverage requires a notched trowel dragged at a consistent angle — typically 45 degrees — to create ridges that collapse evenly when the tile is pressed in. This technique achieves the 80–95% back coverage recommended for most installations (95% in wet areas). Simply globbing on extra mortar traps air and prevents the tile from bedding flat. The result is a hollow-sounding tile that is prone to cracking under load and may eventually debond entirely. Always back-butter large-format tiles in addition to troweling the substrate for full coverage.

Grouting too early introduces moisture into mortar that hasn't finished its chemical curing process. This can weaken the bond, cause tiles to shift slightly as you work across the surface, and lead to grout cracking at the joints once the mortar finishes curing and contracts slightly. Always follow the mortar manufacturer's cure time — it varies by product, humidity, and temperature. Cooler or more humid conditions extend cure time. When in doubt, wait longer; the extra hours cost nothing compared to the damage premature grouting can cause.

The Porcelain Enamel Institute (PEI) rating system grades tile surface hardness on a scale of 0 to 5 based on resistance to abrasion. Wall tiles typically carry a PEI rating of 0 or 1 — adequate for vertical surfaces that receive no foot traffic, but prone to chipping and cracking underfoot. Floors require at least PEI 3 for light residential use, and PEI 4–5 for high-traffic areas. Additionally, many wall tiles have a higher water absorption rate than floor tiles, which can cause structural failure in wet floor applications. Always check the manufacturer's rated use before purchasing.

Adding a second layer of tile is only viable if the existing tile is fully bonded (no hollow spots), the substrate can handle the added weight, and the combined thickness won't create transition issues at doorways or conflict with fixtures. Hollow or cracked existing tiles must be removed because they signal a compromised substrate underneath — and new tile bonded over an unstable surface will fail in the same way. Before tiling over existing work, tap every tile with a coin or knuckle and remove any that sound hollow. When in doubt, a full removal gives you the chance to inspect and waterproof the substrate properly.