Question 1

Is my floor stiff enough to tile?

Accepted Answer

The standard is L/360 under total load — the floor may deflect no more than the span in inches divided by 360. A 15 ft span may move 1/2 inch. Natural stone is twice as strict at L/720. In practice on a wood floor that means the TTMAC detail: two layers of plywood totalling about 1-1/4 inch, or one structural subfloor plus 1/2 inch cementitious backer board, or an uncoupling membrane over a sound subfloor. The quick check before you buy tile: walk the floor and watch a glass of water on it, and bounce on mid-span between joists. If the floor moves, tile will crack and grout will fail first — and no mortar, membrane or grout product fixes a floor that flexes.

Question 2

How flat does the floor have to be before tiling?

Accepted Answer

Flat matters more than level, and large tile is unforgiving. For tile with any edge 15 inches or longer, the common requirement is 1/8 inch in 10 feet and 1/16 inch in 2 feet. For smaller tile, 1/4 inch in 10 feet. Check with a straightedge in several directions before anything is mixed. Out-of-flat is what causes lippage — one tile edge sitting proud of its neighbour. On a 24 inch tile a 1/8 inch hump in the substrate shows as a visible, catchable edge. Fix it with self-levelling compound or a patch first. Levelling clips reduce lippage; they do not fix a wavy floor.

Question 3

What goes under tile in a bathroom?

Accepted Answer

On a floor: the structural subfloor, then either 1/2 inch cementitious backer board set in thinset and fastened, or an uncoupling membrane. Not plain plywood on its own, and never OSB as the direct bonding surface. On a shower wall: cement board, coated glass-mat board, or a foam board system — plus waterproofing. Regular drywall does not belong in a shower. Green board is moisture-resistant, not waterproof, and is not a shower substrate. Backer board is not waterproof either. It survives water; it does not stop it. The waterproofing is a separate layer over the board, or a board system that is waterproof by design.

Question 4

Does a shower need waterproofing behind the tile?

Accepted Answer

Yes, always. Tile and grout are not waterproof — water passes through grout and sits behind the tile. Something has to stop it reaching the framing. Two accepted approaches: a sheet or liquid-applied membrane over the backer board, or a bonded waterproof board system. Both must be continuous — walls, the curb, the corners and up to the height the water reaches. On a shower floor, the pan membrane turns up the wall at least 152 mm, and the mortar bed is at least 25 mm at the drain, sloped 6 mm per 305 mm — roughly 1/4 inch per foot — so it drains rather than pooling. A shower that was tiled without a membrane will not tell you for a year or two. Then it tells you through the ceiling below.

Question 5

Which tile is safe on a shower floor?

Accepted Answer

Smaller tile, because the grout joints give grip and the slope works. TTMAC's guidance for wet areas is 100 mm by 100 mm (4 by 4 inch) or smaller on shower floors. Large tile on a shower floor fights the slope to drain — the tile is flat and the floor is not, so either the tile rocks or the slope is lost. Mosaic sheets follow the slope in every direction, which is the whole point. Elsewhere in a bathroom, look for a textured or matte surface rather than polished, and check the slip rating if the manufacturer gives one. Polished porcelain and a wet foot are a bad combination on any floor.

Question 6

Why does my tile need a gap around the edges?

Accepted Answer

Because tile, the substrate and the building all move, and a tile field with nowhere to go cracks or tents. You need a soft joint — caulk or a proprietary profile, not grout — wherever tile meets a wall, a cabinet, a tub, a different material, or a change of plane. Inside corners get caulk, not grout, for the same reason. On larger floors you also need movement joints through the field: commonly every 20 to 25 feet indoors, and closer where there is direct sunlight or radiant heat. Over a concrete slab, any existing control joint in the slab has to carry through the tile rather than being bridged.

Question 7

Which tile pattern should I use, and where do I start?

Accepted Answer

Grid is the least waste and the most forgiving of an out-of-square room. Offset — brick pattern — hides small size variation but must not exceed 33% offset on tile 15 inches or longer, or lippage becomes unavoidable because planks are slightly crowned. Herringbone looks best on a large clear floor and costs the most in labour and waste. Waste allowance: 10% for grid, 15% for offset and diagonal, 20% for herringbone or a cut-up room. Start the layout from the sightline that matters — usually the doorway or the longest uninterrupted wall — and work so the cuts land where they are least seen. Never start at a wall and hope: dry-lay the field first and find where the slivers end up.

Question 8

How do I match veining across tiles?

Accepted Answer

With patterned porcelain, count the faces. Manufacturers print a limited number of different faces — often 6, sometimes 12 or more — and a repeat you can see is the commonest complaint about an otherwise good floor. Ask how many faces before ordering, and open several boxes and mix them rather than laying box by box. With natural stone and bookmatched slabs, layout is decided on the floor before anything is set. Lay the whole field out dry, photograph it, and number the pieces. Order all of it in one lot. Dye lot and calibre both shift between production runs, and a box bought three months later will not match even with the same product code.

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