For fixing ceramic tiles or mosaics, use a notched trowel to give a ribbed mortar bed on the substrate, into which the tiles are firmly bedded with a twist and slide action to ensure full contact. Use a 3mm x 3mm notch at 6mm centres for mosaics and thin flat backed wall tiling, a 5mm x 5mm notch at 10mm centres for general wall tiling and 10mm x 10mm notch at 16mm centres for floor tiling. The position of the tiles can be adjusted up to 5 minutes after initial fixing. Open time of the exposed mortar bed is approximately 5-10 minutes, depending on surface porosity and site conditions. It is recommended that tiles with raised or studded back profiles, (or in situations where dampness is likely after tiling), should be buttered to ensure solid bed fixing. Do not trowel out an area of adhesive greater than can be tiled over within a 5-10 minutes period. Surfaces such as rutted concrete and masonry block-work, that are rough or uneven may first be levelled with Arc Floor Levelling Compound and when sufficiently firm (24 – 48 hours later), is followed by an application of Arc Rapid-Set adhesive as a bed of 3 to 6mm thickness. Expansion joints should be planned and installed in large floor areas in accordance with the recommendations of BS 5385. Grouting may proceed as soon as the tile bed is sufficiently firm, which for Rapid-Set will be after approximately 2-3 hours at room temperature. This period will be slowed by lower temperatures and accelerated by higher temperatures.