All backgrounds are to receive the spatter dash treatment before the surfaces are rendered.
- The rendering is to be in one coat, except where applied to metal lathing when two coats are to be used, and be left with a wood float finish. It is to be as uniformly thick as apposite and not less than 8mm or more than 13 mm thick in any part.
- Mesh reinforcement to be incorporated in the rendering where: a)The structure is out of line and the thickness of render required exceeds 13 mm b) The rendering is to be applied over differing structural materials c) The surface of the structural wall will be subject to excessive movement.
- Where the tiling is to be bedded on a thin bed adhesive, the trueness of the rendering is to be such that when tested with a 3 m straightedge, no gap exceeds 3 mm. Where the gap exceed 3 mm but is less than 6 mm, or if the wall is out of plumb by not more than 6 mm, the Engineer may permit a thick bed adhesive to be used or may direct that the defective areas are cut back and made good. Deviations from true or plumb in the surface of the rendering exceeding 6 mm are to be made good. Thin-bed adhesive should not be used for fixing tiles with backs incorporating deep keys or frogs; for these thick-bed adhesive must be used.
- Tiles are to be set out before the work commences so that, a) Cut tiles are kept to a minimum and where they do occur, are as large as possible b) Joints are horizontal and vertical, with horizontal joints aligning in wall that are adjacent.
- Tiles shall be neatly and accurately cut to a close fit where necessary at abutments and around outlets, pipe and the like.
- Movement joints not less than 6 mm wide are to be provided: a) At all internal vertical corners b) At all angles with structural walls and ceilings c) To give bays not greater than 3000 mm X 4500 mm d) Over all structural movement joints
- Joints are to be carried through the rendering to the structural wall and shall be partially filled with approved joint filler and finished flush with sealant recommended by the manufacturer for the situation in which it will be used.
- Glazed edge tiles to be used where edges are exposed.
- Adhesive is to be prepared and applied with a trowel to dry rendering in the manner recommended by the manufacturer. The tiles are to be pressed firmly into the adhesive with a twisting/sliding action, tapped firmly into position and cleaned as soon as the bedding is complete.
- It is essential that the tiles are fixed in position before the surface of the adhesive dries and the work is to be carried out in small areas of not more than 1 m2 at a time.
- The finished surface of the tiles should be plumb and true such that when checked with a 3m straightedge no gap exceeds 3 mm.
- Joints are to be approximately 2 mm wide and where tiles without spacer lugs are used, spacer pegs of suitable and even thickness are to be inserted between the tiles as the work proceeds.
- Joints are to be grouted after the adhesive has set and not less than 48 hours after fixing. The grout should be well worked into the joints so that they are completely filled, and finished slush. Surplus grout is to be cleaned off as the work proceeds using a damp cloth and the units tooled smooth.
Laying Floor Tiles by the Direct Mortar Bedding Method; the areas of concrete substrata to be tiled should be brushed clean and dampened until absorption ceases and the finished floor level is to be established by means of dots and rules:
- The mortar for bedding the tiles shall be prepared in ratio 1:4 by volume cement to sand, mixed in a mechanical mixer to a stiff plastic consistency so that when tamped and fully, compacted into place free water does not bleed to the surface.
- The bedding mortar is to be laid on the concrete substrata 15 to 25 mm thick, except where tiles 10mm thickness or less are used in which case the bedding is not to exceed 15mm, and shall be levelled and tamped with a straightedge board.
- The tiles are to be soaked in clean water for 15 to 30 minutes before fixing and allowed to drain for 10 minutes to remove all surplus water. Fully vitrified tiles do not require soaking.
- The bedding mortar is to be lightly dusted with grey cement sprinkled from a flour sieve and lightly troweled level until the surface becomes damp. The tiles shall be laid on the bedding and tapped firmly into position with a soft faced mallet to ensure a true surface and contact between the tiles and bedding is complete.
- Grouting and other requirements of the semi-dry-mix method described above (laying ceramic tiles) also apply to the direct mortar bedding method.