Key takeaways
- Substrate porosity determines adhesive chemistry: cementitious for porous surfaces, epoxy or polyurethane for non-porous
- New concrete requires 28 days curing before tile adhesive application; tiling earlier traps moisture and causes debonding
- Coverage rates range from 3 to 6 kg per sq m depending on substrate porosity and notch trowel size
- Plywood and metal substrates need specialist epoxy-based adhesives; cementitious types cannot form a mechanical bond
- C2 class adhesives deliver bond strength of 1.0 N/mm² or higher per EN 12004
A tile failure rarely starts at the tile. It starts where the adhesive meets the substrate, in a zone you cannot see once the tile is fixed. The substrate’s porosity, not the tile’s size or format, determines whether a cementitious adhesive can grip or whether it will peel away within months.
How substrate porosity changes adhesive choice
The single factor that predicts adhesive failure before you open the bag is porosity. Cementitious adhesives form a mechanical bond; they need pores to penetrate. Non-porous surfaces offer nothing for them to grip.
Epoxy and polyurethane adhesives work differently. They form a chemical bond that adheres to the surface rather than penetrating it. This distinction drives every substrate decision on site. Here’s a table showing how adhesive type changes on the basis of porosity and why.
| Porosity | Substrate examples | Adhesive type | Why |
| Porous | Concrete, brick, cement plaster | Cementitious (C1/C2) | Adhesive penetrates pores; mechanical lock forms |
| Semi-porous | Cement fibre board, gypsum plaster | Polymer-modified cementitious | Some penetration; polymer improves flexibility |
| Non-porous | Metal, sealed plywood, existing tiles | Epoxy or polyurethane | No pores; chemical bond required |
Get this classification wrong and the bond fails regardless of how carefully the tile is laid.
What tile adhesive to use for concrete and cement screeds?
What happens in week three if you tile in week two? Moisture trapped beneath the tile migrates upward as the concrete continues curing, pushing against the adhesive bond from below. Within months, tiles sound hollow. Within a year, they lift.
New concrete needs 28 days to cure before tile adhesive application. Dampen the surface lightly before applying adhesive to prevent rapid water absorption from the mix. For large-format tiles (600×600 mm and above), use a highly polymer-modified adhesive with extended open time, like Roff Vitrofix Ultra Adhesive, which bonds to cement screeds and concrete.
Coverage on dense concrete runs 3 to 4 kg per sq m with a 10 mm notch trowel. Back-butter tiles above 600×600 mm.
How to fix tiles on brick surfaces?
The same adhesive that worked on concrete fails on dry brick. Brick is more porous and absorbs water from the adhesive mix faster than concrete does. The adhesive skins over before the bond forms.
Preparation determines success:
- Remove loose mortar, dust and efflorescence with a wire brush
- Dampen the brick surface 10 to 15 minutes before application
- Use a larger notch trowel (12 mm) to compensate for surface irregularities
A highly polymer-modified cementitious adhesive handles the uneven profile. Coverage increases to 4 to 5 kg per sq m on rough brick. Check open time; you have 15 to 20 minutes before the adhesive skins in summer conditions.
Tile adhesive for plywood and wooden substrates
Plywood expands and contracts with humidity. If the substrate moves more than 2 mm, the adhesive bond fractures. Therefore, cementitious adhesives cannot bond to plywood; there are no pores to penetrate. Epoxy or polyurethane adhesives are mandatory in these cases.
Substrate requirements:
- Exterior-grade plywood only (interior grades delaminate with moisture)
- Minimum 12 mm thickness
- Fixed to a stable frame with no flex under load
- Joints staggered and sealed
A polyurethane epoxy-based adhesive, such as Roff Master Fix Adhesive, handles the flexibility demands and bonds chemically to the sealed surface. Coverage is lower (2.5 to 3 kg per sq m) because the surface is smooth.
What tile adhesive should you use for cement fibre boards?
Cement fibre board is semi-porous; polymer-modified cementitious adhesives work if the board is tile-ready grade.
Check the board specification before specifying:
- Tile-ready boards are designed to accept adhesive without priming
- Standard boards may need a bonding primer
- Board thickness must support tile weight without deflection
Avoid overloading boards with heavy natural stone. Polymer-modified adhesives (C2 class) provide adequate bond strength at 1.0 N/mm² per EN 12004. Coverage runs 3 to 4 kg per sq m. Ensure the board is fixed to a rigid subframe; any flex transfers to the tile and cracks grout joints.
Fixing tiles on metal surfaces
Cementitious adhesive peels off metal in under six months. No pores means no mechanical bond. The adhesive sits on the surface, and thermal expansion does the rest.
Metal substrates require:
- Degreasing with solvent to remove oil and contaminants
- Rust removal down to bare metal
- No rising damp (metal does not breathe; moisture has nowhere to go)
A polyurethane epoxy-based adhesive is mandatory. Spot bonding is acceptable for wall cladding but not recommended for floors; full bed coverage prevents hollow spots under load. Chemical bond strength exceeds cementitious types, but surface preparation is non-negotiable. Skip the degreasing and the adhesive fails at the contamination layer, not the metal.
Match the substrate, not just the tile
Substrate porosity and flexibility determine adhesive type before tile format enters the conversation. Check cure time for concrete, moisture content for plywood, and structural stability for cement boards. Match the adhesive chemistry to the substrate, and the tile takes care of itself.
