5 DIY tile mistakes
we get called to fix

Tile is the renovation task that looks simple on YouTube and is brutally hard in real life. The cuts are unforgiving. The thinset has a clock. The wall behind the tile is doing more work than the tile itself.

I get a tile rescue call about once a month. The story is almost always the same. The homeowner did the work themselves, it looked decent on day one, and somewhere between three months and three years the floor cracked, the grout fell out, the shower started leaking, or the layout looked wrong from the doorway and they finally admitted it.

Here are the five mistakes I see again and again, and what good tile work actually requires.

1. Bad layout: the off-centre cut at the doorway

This is the most common one and it has nothing to do with skill. It is about planning before the first tile goes down.

A DIY install almost always starts at one wall and works across the room. By the time the installer reaches the opposite wall, the last row is a 2-inch sliver. Or worse, the doorway lines up with a 1-inch cut on the threshold.

A real tile layout starts in the middle. You dry-lay the room, find the centre line in both directions, and shift the centre line until the cuts on both ends are roughly equal and at least half a tile wide. You also line up the grout joints with the doorway, the vanity, the shower curb, and any other visible edge.

The fix once it is laid wrong is a full tear-out. There is no other option.

2. The wrong thinset on the shower wall

Thinset is the cement-based mortar that bonds the tile to the substrate. There are dozens of products and they are not interchangeable.

The classic DIY mistake is using a basic grey thinset on a large-format porcelain tile in a shower. The shower wall flexes a little. Porcelain has almost zero water absorption. Basic thinset bonds to porous things. So the bond fails, the tile pops off, and the homeowner thinks they did something wrong with the trowel.

What you actually need on a shower wall:

• A polymer-modified thinset rated for non-porous tile (Mapei Ultraflex 2, Laticrete 254 Platinum, Schluter All-Set)
• The right notch trowel for the tile size (1/2-inch square notch for 12x24 porcelain)
• Back-buttering on any tile over 8 inches in any dimension
• A coverage check on the third tile (pop it off, look at the back, you want 95% contact)

The thinset also has a working time of about 30 minutes once mixed. You cannot mix a whole bucket and chip away at it for two hours. It skins over and the bond is dead.

3. No movement joints

Tile expands and contracts with temperature and humidity. So does the floor under it. So does the wall behind it. If the assembly has no place to move, something cracks.

The TTMAC Handbook (the industry's bible) requires a soft joint (a flexible silicone or urethane bead, not grout) at every change of plane and at intervals across large floors. That means:

• Where the floor meets the wall
• Where two walls meet in a corner
• Where the tile meets a transition (hardwood, vinyl, threshold)
• Around any plumbing penetration
• Across the floor itself every 8 to 12 feet on interior floors

The DIY install grouts every joint solid. Two winters later the grout in the corner cracks and the homeowner thinks the grout failed. The grout is fine. The wall and floor are moving in opposite directions and they have nowhere to go.

4. Sloppy grout joints

Grout is the part of the install that gets judged from across the room. Bad grout work shows up in three ways: uneven joint widths, smeared grout haze that never came off, and a bowl of grout that started drying before the homeowner finished spreading it.

Real grout work means:

1. Tile spacers used and verified at every cross joint, not eyeballed
2. The substrate bone-dry and the tile fully cured (24 hours minimum) before grouting
3. Grout mixed to a peanut-butter consistency, not soup
4. Worked into the joints diagonally with a rubber float, then struck off at 45 degrees
5. First sponge pass while the grout is still soft, second pass after it sets, then a microfibre haze removal
6. Sealed with a penetrating sealer 72 hours later if the grout is cement-based (skip this if you used an epoxy or pre-mixed urethane grout)

Skip the haze removal and you stare at it forever. Sponge too aggressively on the first pass and the joints sink. Use the wrong float angle and you scoop the grout right back out. There is a learned hand to it.

5. Ignoring waterproofing in showers

This is the one with the largest repair scope of all of them, so I'm putting it last and underlining it.

The tile is not the waterproofing. The grout is not the waterproofing. The cement board is not the waterproofing. There has to be a continuous waterproof membrane behind the tile or under it.

The two systems we use on Ottawa bathroom renovations:

• Schluter-Kerdi: a fleece-backed orange membrane bonded to the substrate with thinset. Every seam, corner, and pipe penetration sealed with Kerdi-Band or pre-formed pieces.
• Liquid membrane (RedGard, Hydro Ban): rolled or brushed in two coats, with reinforcing fabric in the corners and at the curb.

The DIY install puts cement board on the studs, tapes the seams with mesh and thinset, and tiles directly. Water gets through the grout (it always does). Water gets through the seams. The framing rots. Two years in there is a dark stain on the ceiling below or a soft spot on the floor outside the shower. By then the entire shower has to come out and the joists need replacing.

A waterproof membrane is a minor material line on a shower and saves you a full tear-out and rebuild. Skipping it is the single most expensive mistake in DIY tile.

When DIY tile actually works

I am not telling you to never tile. A backsplash in a kitchen is a great DIY project. A small powder room floor with simple square tile is fine. A laundry room. A mudroom.

The rules are: dry areas only, small format tile (12x12 or smaller), simple grid layout, and a substrate that is already flat and solid. Skip showers, skip large-format porcelain, skip mosaics with weird patterns, skip anything where the tile is the waterproofing layer.

If the room is wet, hire it out. If the layout is going to be visible from the front door, hire it out. A pro install is priced by tile size and format, layout complexity, substrate prep, and the waterproofing the room needs, and the work is warrantied. Redoing a bad DIY job costs the original install plus the demo plus the substrate repair plus the grief.