Tiling to plywood/plywood overlaid floors
It is essential that the existing timber floor is stable, clean and in good condition with adequate ventilation beneath the chipboard to prevent atmospheric moisture distortion. The plywood must be WBP/Marine grade screwed down at 300mm centres. All board edges should be fully supported. The board should ideally be a minimum 15-18mm thick. It should be able to support the additional weight without excessive deflection**
Beware of some grades of Eastern European and Far Eastern Plywood which may be susceptible to disintegration when wet. Plywood which has been treated/coated may not be suitable to receive a tiled finish as the coating may inhibit adhesion. To the board
To avoid shrinkage defects in new boards, the moisture content of the timber must match that of the finished installation before it is fixed (pre-conditioning). When received on site, the boards should be unpacked and loosely stacked, preferably with spacing stickers between the pieces to allow air to circulate around the timber. Store length ways, placing heavy weights on top of the timber stack to restrict warping of the boards. The length of time that the timber should be pre-conditioned will vary depending upon how closely the timber matches site conditions. If conditioning for more than two or three days is required, it is wise to re-stack the timber, moving material from inside the stack to the outside. Conditioning for 14 days or more may be necessary.
In areas which may be subject to wetting, plywood must be tanked using Norcros Wet Seal Tanking Membrane
**To check that movement in the floor is not excessive, fill a tumbler to the rim with water and place it on the floor. Stand approximately 1 metre away from the tumbler and jump on the floor. If the water spills out of the tumbler then the floor should be strengthened with an overlay of either 15-18mm WBP Plywood or 10mm Norcros Pro Board.
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 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 larger internal floor areas, intermediate movement joints should be provided to form bays of size not greater than 10m x 10m
d. In larger external flor areas, intermediate movement joints should be provided to form bays of size less than 10m x 10m
e. On suspended floors, stress relieving joints should be inserted where flexing is likely to occur, e.g. over supporting walls or beams.
f. Internal floors, which might be subjected to significant thermal changes, i.e. direct sunlight in atria, or underfloor heating etc, the floor area should be divided up by intermediate movement joints provided at 5m intervals in both horizontal directions to provide 25m2 bays. N.B. These bay sizes may be increased to 40m2 when Norcros Permalayer anti-fracture matting is used.
Fix tiles in a 3-4mm solid bed of Norcros One Part Direct to Wood and allow to dry.
Lay Norcros Permalayer anti-fracture membrane onto the plywood in a 2mm bed of Norcros Rapid Porcelain Grey Adhesive & allow to dry before laying tiles in a 3-4mm solid bed of Norcros Rapid Porcelain Grey, Rapid Porcelain & Stone White, Norcros Rapid Porcelain S1 or Thick Bed Stone & Porcelain adhesive. Allow to dry.
Overlay the plywood with 10mm thick Norcros Pro Board (refer to product data sheet) before laying tiles in a 3-4mm solid bed of Norcros Rapid Porcelain Grey, Rapid Porcelain & Stone White, Norcros Rapid Porcelain S1 or Thick Bed Stone & Porcelain adhesive. Allow to dry.
Overlay the plywood with 15-18mm thick Norcros Pro Board WBP/ Marine grade plywood laid with cross staggered joints and screw fixed to the existing boards at 300mm centres and at 150mm intervals along board edges. Prime back, face and edges with undiluted Norcros Prime Bond and allow to dry before laying tiles in a 3-4mm solid bed of Norcros Rapid Porcelain Grey, Rapid Porcelain & Stone White, Norcros Rapid Porcelain S1 or Thick Bed Stone & Porcelain adhesive. Allow to dry.
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.
Floor tiles, especially natural stone and porcelain can be difficult to cut and good quality tools are required. These can bought or in some in-stances 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.
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 any risk of stain-ing, the tiles should be fully sealed using a proprietary sealer before grouting begins.