15 Common Tile Installation Mistakes to Avoid

Updated April 2026 · 13 min read · By the Tilers4you team, Aurora CO

After 15 years of tiling bathrooms in Aurora and getting called to fix other people’s work, I’ve seen every mistake in the book — most of them multiple times. Some are harmless aesthetic issues that bother the client but won’t cause structural damage. Others are code violations that lead to water damage, mold, rot, and five-figure repair bills.

These are the 15 mistakes I see most frequently. Each one has a clear cause, a predictable consequence, and a straightforward fix — if you catch it before the thinset sets.

Mistake 1: Wrong Adhesive for Wet Areas

What it is: Using mastic (organic adhesive, pre-mixed in a bucket) or any water-soluble adhesive in a wet area like a shower, tub surround, or steam room.

Consequence:Organic mastics are petroleum or latex-based adhesives that dissolve or re-emulsify when exposed to sustained moisture. In a shower, that means the bond between tile and substrate breaks down within 12–24 months. Tiles begin to sound hollow when tapped, then pop off in sections. When I demo a mastic shower, I often find the tile lifts off the wall in sheets with the mastic still tacky on both surfaces — it never properly cured in the constant moisture environment.

How to avoid it:Use only Portland cement-based thinset mortar (ANSI A118.1 standard dry-set, or A118.4 latex/polymer modified) in wet areas. The TCNA Handbook explicitly prohibits organic adhesives in continuously wet or submerged applications. The bucket should say “thinset” or “mortar,” and it should be a dry powder that you mix with water — not a pre-mixed paste.

Mistake 2: Skipping Waterproofing

What it is: Tiling directly over cement board or greenboard in a shower without a waterproofing membrane behind the tile.

Consequence:Cement board (HardieBacker, DuraBacker, Wonderboard) is water-resistant, not waterproof. Water vapor and splashback pass through grout joints, through the cement board, and into the framing. In Colorado’s dry climate, the framing may dry out between uses, slowing damage — but in a heavily used shower, the accumulation exceeds the drying rate. I’ve opened shower walls in Aurora homes where the 2×4 studs behind the cement board were completely black with mold and structurally soft. Replacing framing through a finished wall is a $4,000–$8,000 repair.

How to avoid it:Install a TCNA-listed waterproofing membrane behind the tile — either a sheet membrane (Schluter KERDI, Laticrete Hydro Ban Board) or a liquid-applied membrane (Laticrete Hydro Ban, Mapei Mapelastic AquaDefense). The membrane must run from the shower floor up the walls to at least 72 inches, and cover the full floor area inside the curb. See the TCNA Handbook Method B422 or B415 for shower assembly specifications.

Mistake 3: Grouting Movement Joints

What it is:Filling the joint between the shower floor tile and the wall tile — or the corner between two walls — with grout instead of silicone caulk.

Consequence:The corner between floor and wall is a change-of-plane joint. Tile on the floor moves slightly differently than tile on the wall, because the floor deflects under load and the wall doesn’t. Cement grout is rigid and has essentially zero elongation before failure. When the floor tile moves — even 1/64 inch — the grout at the corner cracks. Cracked grout at the change of plane is the #1 entry point for water to get behind the tile and behind the membrane. TCNA EJ171 specifically requires a movement joint (flexible sealant) at every change of plane, change of material, and perimeter of every tile installation.

How to avoid it:Every inside corner in a shower — floor-to-wall and wall-to-wall — gets silicone sealant matched to the grout color, not grout. The joint width should be 1/8” minimum. Color-matched silicone from the tile manufacturer (Laticrete Spectralock Caulk, Mapei Keracaulk) matches the grout color almost exactly.

Mistake 4: Wrong Substrate

What it is: Using standard drywall or greenboard (moisture-resistant drywall) as the substrate behind tile in wet areas.

Consequence:Standard drywall has a gypsum core that dissolves when wet — it will literally crumble out of the wall behind the tile once moisture penetrates the grout joints. Greenboard has a moisture-resistant paper facing but the same gypsum core. IRC Section R702.4 explicitly prohibits the use of regular gypsum board (including moisture-resistant gypsum board) as a substrate for tile in shower areas. Yet I see it on jobs every month — usually on contractor flips and budget remodels where someone substituted drywall for cement board to save $80.

How to avoid it:In wet areas, the substrate must be cement board (ASTM C1325 compliant), foam board (like Schluter KERDI-BOARD, which is both substrate and waterproofing in one), or an approved backer that is dimensionally stable when wet. Ask your contractor what substrate they’re using before installation begins — and look at the material before it goes behind the tile.

Mistake 5: Insufficient Thinset Coverage

What it is: Setting tile with too little thinset beneath it, leaving voids between the tile back and the substrate.

Consequence:Voids beneath tile are stress concentrators. A tile with 50% coverage can crack under normal foot traffic in areas where the void spans the load point. In wet areas, voids collect water that cannot drain — it sits, grows mold, and eventually compromises the substrate. ANSI A108.5 requires 80% minimum coverage for floors and 95% for wet areas. The tap test — tapping tile with a coin after cure — reveals hollow areas as a dull thud rather than a solid click. Hollow tile in a wet area is a defect that requires removal and resetting.

How to avoid it:Use the correct trowel size for the tile being set (see the tool article for the size chart), back-butter the tile in addition to combing the substrate for any tile over 12”×12” or in wet areas, and verify coverage by lifting the first tile of each new session before the thinset skins. The back of the lifted tile should show uniform mortar transfer across at least 80% of the surface (95% for wet areas).

Mistake 6: Wrong Trowel Size

What it is: Using a trowel with notches that are too small for the tile size being installed.

Consequence:A 1/4”×1/4” V-notch deposits about 3/32” of thinset on the substrate after the notch ridges collapse. For a 4”×4” tile, that’s adequate for 80% coverage. For a 16”×16” tile, the same trowel leaves massive voids because the trowel can’t deposit enough mortar volume to fill the relief (ridges and valleys) on the back of a large tile. Additionally, large tiles flex slightly during installation — they need enough mortar beneath them to support that flex without cracking.

How to avoid it:Match trowel notch size to tile format using the tile manufacturer’s recommendation and the general guide: 1/2”×1/2” square-notch for tiles 12”×12” to 18”×18”, 3/4”×3/4” for 24”×24” and larger. When in doubt, go larger — excess thinset squeezes out at the joint and can be cleaned; insufficient coverage can’t be added after the fact.

Mistake 7: No Movement Joints in the Field

What it is: Running tile from wall to wall across a large floor or wall surface with no expansion joints.

Consequence:Tile assemblies expand and contract with temperature changes. In a bathroom that goes from 65°F to 85°F during a shower cycle, the tile assembly expands. Cement grout has no ability to accommodate that movement. Over hundreds of cycles, the cumulative stress causes grout cracking and eventual tile cracking or tenting (tile lifting off the substrate in a convex buckle). Denver’s temperature swings are significant — even indoor tiles experience 20–30°F swings seasonally.

How to avoid it:TCNA EJ171 requires movement joints every 20–25 feet in interior floor tile, every 8–12 feet in exterior tile, and at all changes of plane (floor-to-wall corners) and material boundaries. For a typical bathroom floor under 200 square feet, one perimeter movement joint (silicone at the wall junction) is usually sufficient. For larger continuous tile installations, intermediate joints at 20–25-foot intervals.

Mistake 8: Ignoring Lippage

What it is: Allowing height variation between adjacent tiles that exceeds tolerance.

Consequence:Lippage over 1/16” catches toes on a floor and creates a visible defect on a wall. It also traps dirt, makes cleaning more difficult, and indicates underlying substrate flatness problems. ANSI A108.02 Section 4.3.7 defines the tolerance: 1/16” for tiles with a side 15 inches or less; 1/8” including inherent warpage for larger tiles. Lippage from inadequate substrate prep doesn’t go away when you seal or wax the floor — it’s there until the tile is removed.

How to avoid it:Proper substrate prep (grinding or filling to within 1/8” in 10 feet, or 1/16” in 10 feet for large format), correct thinset coverage, and a lippage clip leveling system for any tile 12” or larger. The clips guarantee planarity mechanically rather than relying on installer eye.

Mistake 9: No Dry Layout

What it is: Beginning to set tile without first placing tiles dry (without thinset) to plan the layout, cuts, and centering.

Consequence:Without dry layout, you may discover at the far wall that the last row of tile is 2 inches wide in an 18-inch tile run — a sliver that looks unprofessional and can’t be cut cleanly with a wet saw at that width without risking breakage. Or you discover that the pattern you chose places a cut tile centered on the doorway. Or the accent strip lands right behind the toilet, invisible, instead of at eye level on the feature wall. All of these are preventable with 30 minutes of dry layout before any thinset is mixed.

How to avoid it:Snap a chalk line on the floor at the room’s visual centerline. Lay tiles out dry from center to wall in both directions to see where the cuts will land. Adjust the starting point to avoid slivers (less than half a tile width at the wall) and to center the pattern on the primary focal point. Photograph the dry layout before you pull it up.

Mistake 10: Poor Cuts

What it is: Making cuts with incorrect tools, producing chipped edges, diagonal fractures, or irregular cut lines.

Consequence:Chipped cuts at exposed edges (the cut edge faces outward at a doorway or along a baseboard) are permanent visible defects. A chip on a cut edge of 3/16” polished porcelain is immediately obvious. If the cut edge will be hidden by baseboard tile or a profile, a small chip is acceptable; if it faces out, it’s a reject.

How to avoid it:A quality wet saw with a sharp diamond blade (replace the blade every 500–1,000 linear feet of cutting for porcelain) produces clean cuts with minimal chip on the lead face. Cut technique: move the tile slowly and steadily through the blade, let the water flow cool the cut, never force the tile. For L-cuts and notch cuts, use the wet saw to make the two straight cuts, then score the connection with an angle grinder. A snap cutter is acceptable only for basic ceramic wall tile — never for porcelain, glass, or stone.

Mistake 11: Mixing Dye Lots

What it is: Installing tile from multiple dye lots (production batches) in the same continuous field.

Consequence:Tile manufactured in different production runs can vary slightly in tone, shade, and finish — even if the SKU is identical. Under artificial light, the variation may be subtle. Under natural light, or viewed at an angle, it can look like you deliberately installed mismatched tile. Dye lot variations are not covered by manufacturer warranty and are not correctable without removing and replacing tile.

How to avoid it:Order all tile for a continuous installation from the same shipment. Check the dye lot number printed on the box when the material arrives — if you have boxes from two different dye lots, use one lot for one room and the other for an adjacent area where a visual break is natural. Always order 10–15% extra material from the same dye lot for future repairs. Tile discontinued from production or changed between dye lots is very common in the mid-range market.

Mistake 12: Skipping Grout Sealer

What it is: Leaving sanded cement grout unsealed after installation.

Consequence:Cement grout is porous. Unsanded grout and sanded grout both absorb water, oil, and particulates into the pore structure within weeks of installation. Wine, cooking oil, mud tracked from outside, and soap film all stain cement grout permanently if it’s not sealed — the stain is in the pore structure, not just on the surface. Bathroom grout without sealer grows mold in the micro-pores within months. Aurora’s dry climate slows surface mold compared to coastal cities, but subsurface contamination still occurs.

How to avoid it:Apply a penetrating (impregnating) sealer to sanded grout 48–72 hours after installation, once fully cured. Reseal annually or whenever the water-bead test fails (water absorbs into the grout within 5 minutes rather than beading).

Mistake 13: Wrong Grout Type for Joint Width

What it is: Using sanded grout in joints narrower than 1/8 inch, or unsanded grout in joints wider than 1/8 inch.

Consequence:Sanded grout contains fine silica sand as a filler that gives it body and controls shrinkage in wider joints. In a joint narrower than 1/8 inch, the sand particles bridge the joint instead of packing it — you get surface grout with voids underneath, and the grout cracks during cure. Additionally, the sand will scratch polished tile surfaces (marble, glass, polished porcelain) during application. Unsanded grout has no filler and shrinks significantly as it cures — in joints wider than 1/8 inch, it cracks during cure because there’s not enough filler to restrain the shrinkage.

How to avoid it:Match grout type to joint width: sanded (Laticrete 1500, Mapei Keracolor S) for joints 1/8 inch and wider; unsanded (Laticrete 1600, Mapei Keracolor U) for joints under 1/8 inch. Epoxy grout works in any joint width, has no shrinkage, and needs no sealer — but it’s harder to install and costs 3× more than cement grout.

Mistake 14: Rushing Cure Time

What it is: Walking on tile before thinset cures, grouting before thinset cures, or using the shower before grout cures.

Consequence:Thinset continues to develop compressive strength for 28 days after placement, but achieves most of its working strength in the first 24–72 hours. Walking on tile before 24-hour cure displaces tiles in the mortar bed — you can actually walk across a large tile floor and feel it shift under foot. Once thinset begins to set (around 4–6 hours), that displacement is permanent and the tile is crooked. Grouting before 24-hour thinset cure forces moisture from the grout into the thinset, diluting the cement chemistry and reducing both thinset and grout strength. Using a shower before grout has cured 24–72 hours (depending on product) washes uncured grout out of the joints.

How to avoid it:Post a sign. Do not walk on new tile floors for 24 hours minimum after setting. Do not grout until thinset has cured 24 hours (read the product data sheet — some rapid-setting thinsets allow grouting in 3–4 hours, but standard modified thinset is 24 hours). Do not use a newly grouted shower for 24 hours after grouting, and do not apply sealer for 48–72 hours after grouting.

Mistake 15: Mastic in Wet Areas

What it is:This deserves its own entry, separate from Mistake 1, because it appears in a different context. Many homeowners and contractors use mastic for tub surrounds — the three-wall area around a bathtub — believing it’s less wet than a shower. It is not. A tub surround has water splashing against walls daily, steam accumulating at the ceiling, and moisture wicking from the tub deck into the lower wall tile.

Consequence:Mastic fails in tub surrounds on the same timeline as showers — typically 18–36 months before tiles begin popping. When I demo a failed mastic tub surround, the substrate behind it is usually saturated, and the mastic itself has a gummy, partially dissolved consistency. The combination of tile adhesive failure and saturated substrate means the entire tub area needs to be rebuilt, not just retiled.

How to avoid it: Thinset mortar everywhere there is water exposure. The TCNA Handbook and tile manufacturer warranties both prohibit organic adhesives in wet areas, and tub surrounds qualify. The cost difference between mastic and thinset on a typical tub surround job is less than $30 in materials. There is no legitimate cost justification for using mastic in a wet area.