Ceramic Tile on Concrete vs. Wood: What Changes Depending on Your Subfloor
- ceramiquecostainc
- Jul 8
- 6 min read
Most homeowners focus on choosing the tile. What gets less attention — but matters just as much — is what is underneath it. Concrete and wood subfloors require very different preparation processes, different materials, and carry different risks if the installation is not done correctly. Here is what actually changes depending on what is under your floor.
In this article
01 The basics
How to know which subfloor you have
In most Quebec homes, the subfloor type depends heavily on which floor you are renovating. Basement and ground-level floors are almost always poured concrete slabs. Upper floors — kitchens, bathrooms, and living areas on the second storey — are typically built over wood framing covered with plywood sheets.
Concrete slab
Basement floors (sous-sol)
Ground-floor slabs
Garage floors
New construction on grade
Wood subfloor
Upper-storey bathrooms & kitchens
Floors over a crawlspace
Floors over a heated basement
Most pre-1980 home construction
If you are unsure, your installer will assess the subfloor before any work begins — it is one of the first things evaluated on site, because the entire installation approach depends on it.
02 Concrete
Tiling over concrete: what the process involves
The main advantage of a concrete subfloor is that tile can be bonded directly to it — no intermediate layer is required in most cases. Concrete is dense, rigid, and dimensionally stable, which is exactly what ceramic and porcelain tile need. The main challenge is ensuring the slab is properly prepared before any tile is set.
1 Moisture testing
Concrete slabs transmit moisture from the ground. A relative humidity test (ASTM F2170) confirms whether the slab is within safe limits for tile adhesive. This step is mandatory — skipping it is the leading cause of tile failures on concrete.
2 Crack inspection and repair
Any crack in the slab will eventually transmit movement to the tile above. All cracks must be filled and, where movement is likely, an uncoupling membrane is used to isolate the tile from the slab.
3 Surface cleaning
Old adhesive, paint, oil stains, and dust must be completely removed. Contamination prevents the thinset from bonding properly to the slab.
4 Levelling
Concrete is rarely perfectly flat. A self-levelling compound corrects high spots and dips before any tile is set — especially critical for large-format tiles, which will crack or lift over uneven surfaces.
5 Tile installation with appropriate thinset
On a moisture-tested and properly prepared slab, tile is bonded with a polymer-modified thinset sized for the tile format being installed.
New concrete: patience required
A newly poured concrete slab must cure for a minimum of 28 days before any tile work begins. Installing tile on uncured concrete — even if it looks and feels dry — is one of the most reliable ways to cause a full installation failure within the first year.
03 Wood subfloor
Tiling over wood: what the process involves
Wood and tile are fundamentally incompatible without an intermediate layer. Wood expands and contracts with changes in humidity and temperature — ceramic tile does not. If tile is bonded directly to a wood subfloor, that movement will eventually crack the tile, break the adhesive bond, or pop the grout joints. This is not a question of if, but when.
The solution is an intermediate layer between the wood and the tile — typically a cement backer board (panneau de ciment) or an uncoupling membrane — that provides the rigid, stable surface that tile needs without being affected by the wood's seasonal movement.
1 Structural assessment
The plywood must be at least 5/8" thick, and the floor joists must be structurally sound with no excessive flex. A floor that bounces underfoot will crack tile regardless of what underlayment is used.
2 Plywood inspection and repair
Loose boards, damaged sections, squeaks, and soft spots must all be addressed before any underlayment is installed. The plywood must be fully fastened to the joists with screws — not just nails.
3 Cement backer board or uncoupling membrane
A cement backer board (such as Durock or Hardiebacker) is embedded in thinset over the plywood and screwed down. Alternatively, an uncoupling membrane (such as Schluter Ditra) provides a thin, lightweight alternative that also adds waterproofing capability.
4 Levelling
Any height differences at backer board joints are corrected with a feather-finish compound before tiling begins.
5 Tile installation
Tile is then set over the backer board or membrane using a flexible, polymer-modified thinset appropriate for wood-subfloor applications.
What to avoid entirely
Particle board, chipboard, OSB, and interior-grade plywood are not suitable underlayments for tile. They absorb moisture, swell, and delaminate — and any tile installed over them will fail. If these materials are present, they must be replaced before installation begins.
04 Side by side
The key differences side by side
Concrete
Tile can bond directly — no intermediate layer required in most cases
Moisture testing is mandatory before starting
Cracks must be filled or isolated with a membrane
New slabs need 28 days to cure first
Self-levelling compound corrects unevenness
Generally more straightforward once moisture is confirmed
Wood
An intermediate layer (backer board or membrane) is always required
Structural flex must be assessed — a bouncy floor cannot be tiled
Plywood must be at minimum 5/8" thick and fully screwed down
Particle board, OSB, and chipboard must be replaced first
Floor height increases — transitions to adjacent rooms need planning
More steps, but very reliable when done correctly
05 Large format
Large-format tiles: why subfloor matters even more
The larger the tile, the less tolerance there is for subfloor imperfections. A 60×60 cm tile that bridges a 3 mm dip in the subfloor will eventually crack under foot traffic. A 120×60 cm tile is even less forgiving — any unevenness translates directly into stress on the tile body.
This is why large-format tile installations — which are increasingly popular in 2026 — require a particularly thorough subfloor assessment. On concrete, this means precise levelling with self-levelling compound. On wood, it means verifying that the joist spacing and plywood thickness meet the deflection requirements (L/360) before anything else happens.
The practical rule
Industry standards require that subfloor flatness meets 3 mm over 3 metres (1/8" over 10 feet) before large-format tile installation begins. Your installer should verify this with a straightedge before any tile is purchased or cut.
06 Common mistakes
The most common mistakes — and what causes them
Skipping moisture testing on concrete
Leads to adhesive failure, tile lifting, and mold under the surface — often within the first year.
Tiling directly over wood
Without a backer board or membrane, wood movement will crack the tile or break grout joints within months.
Ignoring flex in the floor
A wood subfloor that bounces will always crack tile, no matter what underlayment is used. The structure must be fixed first.
Using the wrong thinset
Standard thinset is not appropriate for all subfloor types. Wood applications require a flexible, polymer-modified formulation.
Tiling over new concrete too soon
Concrete needs 28 days to cure. Tile installed before that point will fail as the slab continues to shrink and off-gas moisture.
Not planning for height changes
A backer board adds height to a wood subfloor. Transitions to adjacent rooms need to be planned before installation begins — not after.
The tile is what you see. The subfloor is what makes it last. A beautiful tile installed over an unprepared or mismatched subfloor is a renovation that will need to be redone far sooner than it should. A thorough subfloor assessment and preparation is not a detail — it is the foundation of the entire installation.
At Ceramique Costa, every installation begins with a proper subfloor assessment. If you are planning a tile renovation and want to know what your subfloor requires, our team can walk you through it — before you commit to anything.
Not sure what your subfloor needs?
Our team will assess your space and tell you exactly what preparation is required — before any tile is purchased. Book a free consultation
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