Can you advise exactly how I should lay my riven slate tiles outdoors?
If you are referring to our natural riven 10mm thickness slate tiles then these should to be laid onto a solid concrete base, as you would indoors.
It is recommended that you have a fully working DPM damp proof membrane (it is worth consulting your builder to get this part right), as your aim is to prevent the rising of moisture from the ground below which over time will break cement bonds and create damp (darker) patches within the tiles themselves. Once your concrete is prepared (again consult a professional builder if you are not 100% sure as every installation is different) you are ready to start tiling. It is advised that once the base is fully dry that you acrylic bond the floor, this product improves adhesion and reduces the porosity of the base you intend to tile onto.
You should lay our slate tiles onto a flexible tile adhesive (preferably an S2 type) applied with a notched trowel thus creating a full bed of adhesive (this ensures that every part of the slate tile is supported). Natural slate tiles of this thickness will break if 'dot and dabbed' or laid upon a fully tempered concrete base, maybe not initially but over time the floor is proven to fail if installed in this way.
Next step once tile adhesive is dry is to give the slate tiles a good clean, making sure that the surface of the tile is free of any residual cutting dust or adhesive product.
Once the tiles are 'completely dry' it is time to apply the first coat of sealer, (please see our 'How to...' guides) this takes no time at all to do but is a very important step in the installation process. It is recommended that customers seal slate before grouting to ensure that grout cannot penetrate the natural pores of the slate and subsequently staining them, it also aides the easy cleaning of excess grout from the surface of the tile during grouting.
Now you are ready to grout. We would recommend a flexible grout suitable for an external application. When grouting it is advisable to ensure that the grout is firmly pushed into the grout joints, this will make for a stronger, water tight slate floor.