Natural stone is subject to considerable variations in tone and vein.  It is therefore advisable to purchase enough for your entire project at the same time and to lay the tiles out before fixing to ensure that a satisfactory mix is obtained.
The best substrate for fixing stone is a solid bed.  Where fixing onto any other substrate care should be taken to ensure that it will not deflect more than half a millimetre when a heavy load is placed on it.  Failure to do this will lead to cracking of the stone tiles.
Fast setting cement based tile adhesives are most appropriate for stone installations using the solid bed method.  Light coloured stones should be fixed with white adhesives to prevent discolouration of the stone.  Where fixing on wood or under floor and under tile heating a flexible adhesive should be used.
Before grouting it is advisable to apply an anti-stain impregnator treatment to ensure that any grout residue is easy to remove and avoid any possible staining by the grout.  Use a cement based grout and add a flexible additive where flexible adhesive has been used.  If fixing tumbled or unfilled stone use a slurry grout to ensure that all cavities are filled.

For exterior stone project we recommend the following installation method.

Whilst preparing the exterior paving slab, ensure clean, dry and seal with appropriate sealant. This prevents any foreign ingress of dirt into the paving during installation. For this we recommend in most external cases LTP Mattstone. This can be provided and delivered at the same time as your Exterior Stone tiles or paving.
The sub-base for which you will be laying your paving should have little (<1.0mm) or no deflection. The sub-base should have a construction of a minimum of 150mm type 1 MOT compacted to your chosen level or even a level base of concrete if you wish.
Paving should then be laid upon a solid layer of mortar, 4:1 with a strong addition of pva, Butt jointing provides the better finish with the 1 – 2 mm seams filled with KDS prior to sealing the finished project with a LTP product

Our installation team leader will assist with all enquiries regarding the finer details of installation

Exterior Stone recommends that in all cases you consult the adhesive and grout manufacturers’ instructions to ensure that a satisfactory job is done and future problems are avoided.