Fixing with tile adhesive or tiling cement (interior or exterior)
To use tile adhesive or tiling cement, the support should be completely dry, clean and level (no gap greater than 7mm under a 2m long straight edge). Tiles should not be fixed directly to a concrete base or screed unless it has cured for a minimum of 30 days. A rule of thumb guide is that the concrete support should cure for as many weeks as its thickness in cm.
Only use adhesives that are light in colour, cream or white, never grey, and check that the product is suitable for natural limestone (see below under ‘Staining’ and ‘Tile Adhesives’) and that the technical specification covers the size and thickness of the tiles to be fixed, particularly for vertical applications.
Proprietary manufacturers of tile adhesives for natural stone include Mapei, Sika, Laticrete, BAL and Norcros. They supply a range of adhesives including products for thicknesses up to 35mm, and products with increased flexibility.
Never butt joint. The joints (5mm minimum width outside and 2mm indoors) should be realised a minimum of 24 hours after fixing. The joints should be pointed with a grouting mortar suitable for stone (dosage 300 kg/m3 - see above under ‘Grouting Mortar’), or with a proprietary ready to use grout. Grouting should proceed one joint at a time with a spatula. Fixing mortar should never be used to grout. Clean the tiles as the work advances with water and a clean sponge.
The surface should be divided by expansions joints (see details above under indoor and outdoor fixing respectively).
Expansion joints existing in the main building structure must be continued through the screed and the tiling. The expansion joints dividing the tiling area are only inserted in the adhesive and the tiles. The peripheral joints are 5 mm for a heated floor, 3 mm for interior or exterior floors.
According to French regulations the maximum surface area of a tile fixed by adhesive is limited to 3600 cm2 (e.g. 600 x 600mm) with the length limited to 3 x the width. The maximum length is 800 mm for interior floors and 600 mm for exterior floors. The thickness can vary according to the average bending strength of the stone concerned, from 10 to 40mm.