How To Tile Onto A Concrete Floor
Tiling on a concrete floor
Concrete must be at least 6 weeks old to enable movement caused by drying shrinkage to have taken place. The concrete must be clean, dry and free from dust, laitance and any other contaminants which may act as a release agent, preventing the adhesive from bonding to the concrete. If the concrete is dusty, dry brush with a wire brush and remove the loose dust. Brush apply Norcros Prime Bond diluted 1:4 with water, to reduce the absorbency of the concrete and suppress dust. The concrete may be levelled using either Norcros Pro 50 or Norcros Pro 30 levelling compound.
Power Floated Concrete has a shiny finish which inhibits adhesion, for this reason it should be prepared by either:
- Mechanically abrading to expose the coarse aggregate.
- Removing all traces of dirt, dust etc. prior to applying a slurry bonding coat consisting of 2 parts cement-based adhesive: 1 part Norcros Prime Bond using a brush or roller. The slurry bonding coat should be allowed to dry before fixing commences.
The general rule is to work from the centre outwards. Measure the width and length of the floor and draw a cross in the centre. From the central cross lay out the dry tiles allowing a minimum 3mm wide gap between the tiles to allow for movement stresses within the floor during service. These gaps will be filled with grout once the tiles have been fixed and the adhesive dried. Make sure there are no awkward cuts, some adjustment may be necessary. Always be aware of how the floor will look when you enter the room.
To counteract movement stresses, which can result in tiles cracking and/or debonding, in accordance with British Standard BS5385-3:2014, movement joints should be provided:
a. Over existing and/or structural movement joints.
b. Perimeter movement joints should be inserted at door thresholds and where the tiling abuts restraining surfaces such as perimeter walls, columns, curbs, steps and plant fixed to the base
c. In large floor areas, intermediate movement joints should be provided at 8-10 metre intervals.
More information on the provision of movement joints is available in the Norcros ‘How To’ Sheet for ‘Movement Joints in Tiled Installations’.
Floor tiles, especially natural stone and porcelain can be difficult to cut and good quality tools are required. These can bought or in some instances hired. A slide cutter and nippers are essential, however an electric wet cutter will make the job easier. For intricate cuts a cardboard template will help to achieve more accurate results.
Fix tiles in a cement-based adhesive such as Norcros Fast Set Rock-Tite, Norcros Rapid Porcelain Grey or White, Norcros Rapid Porcelain S1 or Norcros Thick Bed Stone & Porcelain Adhesive. Refer to the packaging or product data sheets for information regarding mixing ratios. Stir until a smooth lump-free consistency is achieved. Mix only enough material that can be used within the pot life of the product (around 30 minutes at 20oC). N.B. This will be extended in cold weather and reduced in warm conditions.
Using a suitable notched floor trowel held at a 45o angle, spread the adhesive onto the floor to form parallel ribs into which the tiles should be pushed with a firm twisting action, this will collapse the ribs of adhesive and produce a 3-4mm solid bed of adhesive beneath the tiles. Work in small areas and discard any adhesive that begins to dry or ‘skin over’. Tiles with deeply keyed back profiles may need to back buttered. Every so often lift a tile to check that it is in full contact with the adhesive and that no voids are left in the adhesive bed. Wipe off any adhesive residues from the surface of the tiles using a damp sponge before the adhesive sets. Remove deposits of adhesive which may build up in the gaps between the tiles.
DO NOT WALK ON THE TILES FOR AT LEAST 2-3 HOURS, or until the adhesive has set.
Allow the adhesive to dry.
Use either Norcros Flexible Wide Joint Floor & Wall Tile Grout or Norcros 4 into 1 Grout. Clean out any dust, dirt and adhesive from between the tiles and make sure that the joints are dry.
Approximately 4-5 parts grout powder should be added to 1 part water, ensuring that the powder is added to the liquid to prevent the product from flash setting. Manually mix the grout to reduce the amount of air incorporated into the mix. Holding a soft rubber grout float at 45o, sweep the mixed grout diagonally across the tiles, ensuring that the grout is pushed fully into the joints. Clean off as much grout from the surface of the tiles as possible and allow the grout to become touch dry. Clean off the grout residues with a damp sponge wiped diagonally across the tiles. Allow the tiles to dry and buff the surface with a dry cloth. Any stubborn residues may be cleaned off with washing up detergent mixed with warm water within 24 hours of grouting.
N.B. Before grouting commences trial a small inconspicuous area to check that the grout does not stain the tiles. If there is a risk of any staining, the tiles should be fully sealed using a proprietary sealer before grouting begins.
Commonly asked questions
In most cases, it is OK to lay tiles directly onto concrete. But make sure the surface is free of any contaminants, dust, moisture, etc, as these can prevent the adhesive from bonding. If the concrete floor is not in good condition, or may be at risk of cracking, an uncoupling membrane is recommended.
An uncoupling membrane can be placed under the title on top of the concrete. This is useful in preventing movement of the foundations transferring to the tiled floor itself.
Usually a backer board or cement board is not required when tiling onto concrete, as the concrete is usually cementitious already.