Tiling to floating chipboard floors
Floating timber floors are generally constructed of either a concrete or timber base or “raft” onto which a dense polystyrene is bonded (approximately 50mm thick). Tongue & groove timber boards, generally flooring grade chipboard are loose laid on top of the insulation to provide a base to receive floor coverings/ finishes. Heating pipes may be bedded in the insulation layer.
The stability/rigidity of the floor is dependent upon:
• The concrete/ timber base beneath the insulation layer being flat.
• The insulation layer being high density and therefore having little compression/deformation.
• The tongue & groove boards should be glued together using a good quality wood glue.
N.B. Chipboard with a wax coating is not suitable as a tiling substrate.
If the structure is considered to be sufficiently free from deflection, the floor will be deemed suitable to receive a tiled finish. To check the rigidity of the floor, a glass tumbler should be filled to the rim with water and placed in the centre of the floor. Standing approximately 1 metre away from the tumbler, jump up and down on the floor. If the water spills out of the glass then the floor would require strengthening.
N.B. It should be noted however that in some installations, even when strengthened with an overlay or an anti-fracture/ decoupling membrane, a floating floor may still not be able to support the additional weight of tiling without excessive deflection.
All board edges should be glued. The board should ideally be a minimum 22mm thick.
To avoid shrinkage defects in new boards, the moisture content of the timber must match that of the finished installation be-fore 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, chipboard must be tanked using Norcros Wet Seal Tanking Membrane
1. Overlay the chipboard with 10mm Norcros Pro Board which may be either laid into a bed of Norcros Rapid Porcelain Grey adhesive or mechanically fixed with suitable zinc or galvanised screw fixings and galvanised 35mm washers under the screw heads at a rate of 12 fixings per board. (Refer to Pro Board product data sheet)
2. Lay Norcros Permalayer anti-fracture membrane in a 2mm bed of Norcros Rapid Porcelain Grey adhesive and allow to dry. (refer to Permalayer product data sheet)
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 25m2bays. N.B. These bay sizes may be increased to 40m2 when Norcros Permalayer anti-fracture matting is used.
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 highly polymer modified adhesive such as Norcros Rapid Porcelain Tile Adhesive Grey, Norcros Rapid Porcelain & Stone Adhesive White,, Norcros Rapid Porcelain S1 or Norcros Thick Bed Stone & Porcelain Grey/White, Norcros Rapid Porcelain S1 adhesive for large format tiles.
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.
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 any risk of staining, the tiles should be fully sealed using a proprietary sealer before grouting begins.