Tiling to plaster walls
Plaster must be fully dry before tiling commences. Minimum drying times are:
- 4 weeks for backing coat + skim coat
- 1 week for skim coat only
The plaster must be in good condition and firmly bonded to the background with no hollow-sounding areas. It should be noted that backing plaster is not sufficiently strong to accept a tiled finish. Tiles should only ever be fixed to the finishing coat. Any loose or hollow areas should be removed and made good.
If the plaster is dusty or has a shiny finish, it should be thoroughly dry brushed with a stiff bristled brush and the dust removed from the surface prior to priming with Norcros Prime Bond diluted 1: 4 with water. Allow to dry
If tiles are being fixed using cement-based adhesives, the plaster should be primed with undiluted Norcros Prime Bond to prevent any reaction occurring between the gypsum plaster and wet cement in the adhesive.
The maximum weight of tiling which plaster is able to support is 20kg/m2, generally equivalent to a ceramic tile with a maximum thickness of 8mm or natural stone with a maximum thickness of 7mm.
Tiling should be set out from the centre of the walls, either the centre of a tile or the joint between two tiles positioned in the centre of the wall, whichever of these two options avoids small cuts of the tiles. Make a gauge rod using a length of straight timber. Along the length of the timber mark out the width of the tiles, leaving a gap at least 2mm wide between each tile. Set out the horizontal position of the tiles so that the same size cuts are made at either side of windows etc. avoiding any small cuts. At the lowest point of the wall to which tiles are being fixed, such as the skirting board, work surface etc. place an uncut tile and draw a line along the top of the tile. Nail a batten below this line, using a spirit level to make sure that it is level. The first line of tiles will rest on this batten. Measure the width of the wall and mark the centre point. Draw a vertical line at this centre point using a spirit level to make sure that the line is straight. Start tiling at the centre point.
To counteract movement stresses, which can result in tiles cracking and/or debonding, in accordance with British Standard BS5385-1:2009, movement joints should be provided:
- over existing and/or structural movement joints
- where tiling abuts other materials and at junctions between different substrates
- at vertical corners
- at 3m to 4.5m centres both horizontally and vertically and in areas where stresses are likely to be concentrated such as at changes of alignment.
- An increase in the frequency of movement joints should be considered if large degrees of thermal movement or vibration are expected within an installation.
More information on the provision of movement joints is available in the Norcros How to Sheet ‘Movement Joints in Tiled Installations’.
Some porcelain & natural stone tiles 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.
In dry areas, or those which will be subjected to light intermittent wetting, i.e. bathrooms and standard domestic showers, ceramic porous body tiles up to 400mm x 300mm or porcelain tiles up to 200mm x 200mm may be fixed using Norcros Ultim8 adhesive. In areas which will be subject to wetting, i.e. power showers, heavy duty showers the plaster should be tanked using Norcros Wet Seal Tanking Membrane prior to fixing tiles in a 3mm solid bed of Norcros Ultim8+ adhesive.
If larger tiles are to be used, the plaster should be primed with undiluted Norcros Prime Bond which should be allowed to dry be-fore the tiles are fixed using Norcros One Part Flexible White or Norcros Standard Set Flexible S1 adhesive.
Using a suitable notched wall trowel held at a 45° angle, spread the adhesive onto the wall 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 2-3mm 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. In areas subject to wetting such as showers, it is essential that a solid bed of adhesive is achieved beneath the tiles. 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.
Allow the adhesive to dry.
Use Norcros Wall Tile Grout. In areas subject to wetting or where movement/vibration is anticipated Norcros Stop Mould Grout, Norcros 4 into 1 Grout or Norcros Super Epoxy may be used.
Clean out any dust, dirt and adhesive from between the tiles and make sure that the joints are dry.
Mix the grout in accordance with the recommendations on the packaging.
Holding a soft rubber grout float at 45°, 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.