Fixing an exterior floor (other than on a concrete slab)
The ground should be stable and well compacted. The support should be absolutely flat and clean. The various layers of the foundation, the fixing screed and the tiling depend both on the nature of the material and the usage of the area: light traffic for pedestrians only, motor cars or occasional heavy duty lorries. For tiles <40mm thick, fixing should be done with a full mortar bed on well compacted sand or preferably on a concrete slab.
Install a damp-proof separation barrier with a non-woven film (geo-textile) between the support and the fixing screed, including a return around the perimeter.
Install drainage around the perimeter 150mm wide and 250mm high with a bed of gravel.
The fixing mortar consists of a cement or cement / hydraulic lime mortar with a dosage of 300 kg / m3. The cement must be exempt of alkaline salts which can cause the appearance of efflorescence. The sand (type 0/4) should be clean, with rejection at 63 micron not exceeding 15%. Fixing on mortar means that the tiles must be bound to the support to guarantee the permanence of the work.
The screed, levelled with a straight edge, should not be compacted before fixing. The area already laid must be protected from foot traffic for 24 hours and from any load for at least 7 days after fixing.
Never use wet slurry to pour into the joints, spreading with a rubber scraper. Although this technique is often used for ceramic or travertine tiles, when used on limestone it will darken the stone and leave it with a dull grey appearance. One will not be able to recover the initial colour and texture of the tiles.
The joints (5mm minimum width) should be pointed a minimum of 24 hours after fixing the tiles. A grouting mortar suitable for stone should be used (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. Never butt joint.
For surfaces over 20 m2 and for any length over 6 metres divide the surface with flexible joints a minimum width of 5 mm large. Expansion joints existing in the main structure must be continued through the screed and the tiling. The expansion joints dividing the tiling area are only inserted in the screed and the tiles.
A minimum 3 mm space should be left around the perimeter to allow for expansion and filled with a non-staining elastomer mastic.
To ensure water run-off, the slope of the support and the tiling should be a minimum of 15mm per metre (1,5%/m). Fixing should be executed during normal climatic conditions (between approx +5°C and +30°C). Do not fix during very hot weather or if there is a possibility of frost within 48 hours after fixing. Do not lay tiles that have been exposed to frost within the previous 48 hours.
Fixing directly onto waterproofing membrane is not permitted. Tiles should de fixed on raised flooring pedestals can be done complying with the recommendations regarding size and thickness of the stone. Check also with the pedestal manufacturer.