Surface dryness Do not wet background surfaces of tiles when fixing with adhesives of any sort.

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1 Tiling Guides & Techniques 3.2 Fixing Tiles Bedding tiles in adhesive for walls and floors Thickness of adhesive Apply adhesive only to the thickness given in the adhesive manufacturer s sitework instructions. Commentary: The upper and lower limits for thickness of the adhesive are specified by the manufacturer. Thin-bed adhesives are normally not more than 3mm finished thickness. Thick-bed adhesives are usually 6mm thick but may be thicker in small areas to obtain an even surface to the tiling Surface dryness Do not wet background surfaces of tiles when fixing with adhesives of any sort Priming background Prime the background surface if and as required by the adhesive manufacture s sitework instructions Timing a. Do not spread more adhesives than can be covered with tiles before the surface of the adhesives begins to dry or form a skin. b. Follow the manufacturer s sitework instructions regarding the open time of adhesive films. Commentary: In practise the open time is likely to be 20 min to 30 min at most. Although the adhesive may remain plastic at this time its property will be inadequate. If moisture penetrates through the joints and collects in voids the tiling may fail and/or other problems caused by free moisture entering the structure may occur Cleaning surfaces of tiling Clean off the adhesives from the surface of the tiles as soon as practicable before it sets. Take care not to disturb the tiles.

2 Internal wall tiling: thin-bed and thick-bed notched trowelling method a. Spread the adhesive on the background to the thickness given in the manufacture s sitework instructions. b. Rib the surface of thin-bed adhesives in one direction only using a notched trowel to the adhesive manufacturer s sitework instructions, do not rib the surface of thick-bed adhesive surface of thick-bed adhesives unless required to do so by the manufacturer s sitework instructions. c. Press tiles on to the adhesive surface with a twisting, sliding action. d. Place all tiles with regular and straight joints not less than 1.5mm wide and tap them firmly into position. Commentary: Where it is essential to have no voids behind tiles the notched trowelling method is not suitable unless it is used in conjunction with the buttering method (see ) Internal and external wall tiling: thin-bed and thick-bed, combined notched trowelling and buttering method a. Use a notched trowel in accordance with the adhesive manufacturer s sitework instructions. b. Spread the adhesive on the background to the thickness given in the manufacturer s sitework instructions. c. Rib the surface. d. Spread the adhesive uniformly over the back of each tile, ensuring that the whole surface is covered. e. Place all tiles with regular and straight joints not less than 1.5mm wide and tap them firmly into position. f. Ensure that the finished thickness of the adhesive bed does not exceed the maximum thickness given in the manufacturer s sitework instructions.

3 Commentary: This method is used where it is essential to prevent moisture collecting in voids behind the tiles, e.g. externally. The time during which adhesive remains workable varies with the conditions and with the type of adhesive. It is not possible therefore to define this period Internal and external wall tiling: thin-bed and thick-bed, buttering method a. Spread the adhesive uniformly over the back of each tile, ensuring that the whole tile surface is covered. b. Place all tiles with regular and straight joints not less than 1.5mm wide and tap them firmly into position. c. Ensure that the finished thickness of the adhesive bed does not exceed the maximum thickness given in the manufacturer s sitework instructions. Commentary: The use of this method is limited to positions where it is difficult or impractical to apply adhesives by means of a notched trowel, e.g. on window reveals Checking of bedding of wall and floor tiling a. Carefully remove one random tile wherever instructed, as work proceeds and before the adhesive is uniformly distributed over the whole area of tile with no substantial areas bare of adhesive in order to provide consistency support for the tiles. b. Where tiling is to be solidly bedded (see , and ), ensure that as far as practicable the adhesive has no voids c. If the bedding appears to be solid carefully remove all adhesive from the tile and its background, butter the tile with fresh adhesive and replace. d. If the bedding does not appear to be solid remove further tiles, as instructed, in the vicinity of the original tile to check whether or not the fault is general. In either case obtain instructions before proceeding. Commentary: Where tiling will be exposed to frequent wetting it is essential to check very soon after commencing tiling that quality of workmanship is adequate to ensure there are no significant voids left behind tiles.

4 If problems are revealed in the earliest stages, action can then be taken to ensure the problem does not recur. Thereafter random checks should be sufficient Bedding floor tiles in adhesive a. Spread adhesive with a trowel in accordance with the adhesive manufacturer s sitework instructions. b. Where the tiles have a raised or recessed pattern on the backs, butter the back of each tile immediately before laying. c. Press the tiles firmly into the adhesive layer and tamp to give the tiling an overall even surface. d. Ensure that tiles are solidly bedded as far as practically possible. e. Lay tiles with straight and regular joints not less than 3mm wide and generally not wider than 10mm. f. Clean any adhesive off the face of the tiles and off the faces of the joints as the work proceeds. Commentary: The maximum thickness of the adhesive depends on its type. Some types may be used up to 5mm or 6mm thick, up to 12mm in small isolated areas. Some may only be used up to 3mm thick; the finished surface will therefore follow the contours of the base. In any case the adhesive manufacturer s sitework instructions should be followed Bedding wall and floor tiles in cement and sand mortar Dampening backgrounds Dampen the backgrounds sufficiently to prevent excessive absorption of water from the mortar bed immediately before its placing. On floors do not wet the base when there is a separating layer Wetting tiles Unless otherwise specified, wet ceramic tiles that are to be bedded in cement and sand mortar as follows. a. Remove the tiles from cartons.

5 Commentary: If tiles are soaked in their cartons the cardboard may cause staining. b. Soak porous tiles in clean water for at least 30min. Remove them from the water and stack them tightly together with the end tiles face outwards to drain on a clean surface. Remove excess water before fixing. c. Fix tiles before they dry out. Commentary: Tiles classified as AIIb, AIII, BIIb and BIII according to BS 6431 : Part 1 : 1983 require this saturation treatment to prevent rapid suction and subsequent failure to develop adequate bond strength with mortar. AI, AIIa, BI, and BIIa tiles do not require soaking Internal and external wall tiling: floating and back filling method a. Float mortar (cement : sand 1:3 to 4) on to the background, trowel to a finished thickness not exceeding 10mm and finish surface with a wooden float. b. Allow the bed to stiffen slightly. c. Spread bedding mortar (cement : sand 1:1 to 2) uniformly over the back of each tile to a thickness of about 2mm taking care to fill deep keys, frogs and all remaining depressions. d. Place each tile and tap it firmly into position to ensure that each tile makes contact over its whole area. e. Adjust the position of any tile within 5 min of fixing. Commentary: It is necessary to permit the floated bed to stiffen to a degree where it will support its own weight and that of the tiles, but it should also be green enough to permit the thin layer of about 2mm bedding mortar to form an intimate bond with it. It is not possible to define the time necessary for the floated bed to arrive at a suitable stiffness as this depends on a number o factors such as suction of the substrate, the temperature and humidity of the air, ventilation rates, etc Internal and external wall tiling: buttering method

6 a. Spread bedding mortar (cement : sand 1:3 to 4) evenly over the back of each tile taking care to fill all depressions. The thickness of the mortar bed is not to be less than 6mm and not more than 12mm, excluding the depth of mortar in keys or frogs. b. Place each tile and tap if firmly into position to ensure that each tile makes full contact over its whole area with the background. c. Adjust the position of any tile within 10mm of fixing. Commentary: This method is only used for small areas of tiling or for situations where it would be impractical to float the walls Cleaning of mortar Do not start of cleaning mortar splashes from the face of tiles until approximately 2 hours after bedding is complete, then clean off all marks, taking care not to disturb the tiles Floor tiling: direct bedding method a. Wet porous tiles (see ), except where they are to be buttered. b. Mix mortar (see 2.2.6) to a stiff consistency so that when it is fully compacted, free water does not come to the surface. c. Spread mortar bed evenly and compact thoroughly to the thickness required, leaving the surface true and flat. d. Spread at any time only the amount of mortar that can be compacted and tiled in one continuous operation. e. Either: 1. Immediately after the mortar bed has been compacted, dust the surface with a layer of cement becomes damp; or 2. Apply a mortar slurry of one part cement and one part sand or a cement-based adhesive to the backs of the tiles. f. Place the tiles in position with the least possible delay after the mortar bed has been laid. Take care to avoid depressing the bed with one of the tile corners as each tile is placed.

7 g. Place all the tiles with regular and straight joints not less than 3mm wide and generally not wider than 10mm. h. Tape the tiles as work proceeds to provide a true and even surface to the tiling Floor tiling: separating layer method a. Check that the base is smooth to allow for free movement of the separating layer. b. Lay the separating layer loose over the base with a lap 100mm minimum to all joints. c. Take care not to damage the separating layer after it is laid. If any part is damaged, cut out the damaged part and replace it with new material with a minimum lap of 100mm at edges over remaining layer. d. For ceramic tiling, follow steps (a) to (h) in e. For terrazzo tiling, follow steps (a) and (c) in and in addition incorporate a light mesh reinforcement in the semi-dry mix bed which should be at least 40mm thick. Lap reinforcement 100mm minimum and tie with wire. Then follow steps (d) to (h) of Commentary: It is always necessary to introduce a separating layer under a cement/sand mortar bed when the base is mastic asphalt. Separating layers are only used under terrazzo tiling where bonding to the base is not recommended Floor tiling: ceramic tiles: semi-dry mix method a. Mix mortar, adding sufficient water to ensure the following: 1. When the mortar is thoroughly mixed a handful of mortar will, when squeezed, retain its shape and not crumble, leaving the hand slightly moist. 2. When a sample is compacted on the base, no film of water forms on the surface. Commentary: The water content ratio is approximately 6:11 (i.e. 27L of water, including water in the sand, to 50kg of cement) to attain the desired moist earth consistency. b. Spread mortar evenly approximately 10% to 15% thicker than the final bed thickness and compact it thoroughly to the bed thickness required, leaving surface true and flat.

8 Commentary: 70mm is the maximum practical thickness. Where falls have to be formed in the bed, its greatest thickness may be 100mm. The minimum thickness of the bed is 40mm. c. Spread at any time only the amount of mortar that cab be compacted, slurried and tiled in one continuous operation. d. Cover the surface of the newly compacted bed with a slurry of a thick, creamy consistency (cement : fine sand 1 : 1), spread to form an even layer approximately 2mm thick. e. Do not wet the tiles unless they are porous, in which case follow the procedure f. Where the tiles have uneven or deep back patterns fill the backs of tiles with cement : sand 1 : 2 or cement-based adhesive, according to the manufacturer s sitework instructions, before laying. g. Place the tiles in position with the least possible delay after the bed has been slurried. Take care to avoid depressing the bedding with one of the tile corners as each tile is placed. h. Place all tiles with regular and straight joints not less than 3mm wide and generally not wider than 10mm. i. Tap tiles with a wooden beater as work proceeds to ensure a true and even surface to the flooring and a firm and full contact between tiles and slurred bed. If a beating or vibrating machine is used commence tapping within 30min of laying tiles. Commentary: It is not possible to define times between laying the bed and placing and tapping in the tiles, as the period is entirely dependent on prevailing conditions. If conditions are such that the bed will dry rapidly the time available could be as little as 20 min. In the most favourable circumstances the limit will be 2 hours Floor tiling: terrazzo tiles: semi-dry mix method a. Mix mortar (see item a. of ) b. Bond the mortar to the base by spreading over the base a slurry of a thick, creamy consistency (cement : fine sand 1 : 1) to form an even layer approximately 2mm thick.

9 Commentary: Slurry is omitted when there is a separating layer (see item (e) of ). c. Spread mortar evenly about 10% to 15% thicker than the final bed thickness and partially compact it, leaving the surface true and flat; the final bed thickness should be at least 25mm. Commentary: Partial compaction of the bed allows tiles of varying thickness to be tapped level. d. Spread at any time only the amount of mortar that can be partially compacted, slurried and tiled in one operation. e. Apply a slurry of a thick, creamy consistency (cement : fine sand 1 : 1) either to the back of each tile before placing or alternatively on the partially compacted bed. f. Place all terrazzo tiles with regular and straight joints between 1mm and 2mm wide. g. Tap terrazzo tiles firmly with a rubber mallet as work proceeds to compact the bed down to the level required and ensure full contact between slurried tile backs commence tapping within 30 min of laying the tiles. h. Wash the tiles after tapping to remove slurry which may have risen to the surface.