Good tile and wood flooring adhesion depends on a correct diagnosis and proper preparation of the substrate beforehand. The following description explains how this should be done. The substrate must be flat, hard, stable, well adhered, clean, dry and have normal absorption.
1. Flatness. How to check the flatness of the substrate?
The substrate must be flat in order to avoid an unsightly appearance or defects that can affect the behaviour of the tiles after fixing them onto the floor (do not confuse flatness with horizontality: a substrate can be flat without being completely horizontal).
1.1 The flatness of the substrate should be checked with a 2m straight edge mounted on 3mm thick spacers. In the case of direct bonding of the tiles, any defects should not exceed ± 3mm (i.e. high points not touching and low points no more than 6mm below) under the 2m straight edge.
2. Hardness. How to check the hardness of the substrate?
The substrate must be both hard and resistant in order to avoid cracking or debonding at a later stage.
2.1 Check the surface hardness by scratching it with a pointed tool in several places. The scratch must be superficial. If the substrate is not hard enough, it must be removed until sound material is reached.
2.2 Also check the in-depth hardness of existing screeds or plastered walls.
3. Stability. How to check the stability of the substrate?
The substrate must be stable in order to avoid deterioration of the tiling at a later stage.
3.1 This check mainly concerns wooden floors laid on joists or battens, wooden panels and, more rarely, partitions.
3.2 The floor must not move when stepped on. Partitions must not flex when pressed by hand. If this is not the case, reinforce the floor with noggings between the joists and replace the boards. Brace unstable partitions.
4. Porosity. How to check the porosity of cement-based substrate/
Cement-based substrates must have normal absorption in order to avoid premature water loss from the cement-based adhesive and to ensure that the bond can develop correctly.
4.1 Pour a little water onto the substrate.
4.2 If the water is absorbed in less than 1 minute the substrate is considered as excessively porous and requires priming.