We would recommend that you use a 25-35mm wet mortar bed on 100mm of well compacted hardcore for most paving situations.
There seems to be some confusion about the way you lay natural stone! The larger surface area is the side of the slab you see when it is laid which means that the joints between the slabs are smaller at the top then they are at the bottom, which also helps the pointing to get a better hold.
We recommend that whenever laying natural stone you should mix your paving from 3-4 different packs (if laying a large area) as this will allow the colours to blend and help to improve any shade variations that may occur between packs, giving your patio a more natural look.
Due to the variations in thickness we recommend you start with a thick slab and tap it down into the mortar until you find the correct level (use a rubber mallet to tap the slab down as it will avoid cracking it). Once you lay the first slab, lay the five spots of mortar for the next slab. You could also lay a strip of mortar where the next joint will be, this will minimise pointing afterwards. Ensure that you check all of the levels and falls during the laying process, you should do this by using a spirit level. This will help you to create a patio with a slight fall on it to ensure it drains properly.
Should you seal natural stone?
We don’t recommend that you have to seal natural stone that is being used outside, however it might help to maintain the colour and keep the paving clean. There are several different sealing products on the market, all producing the same end result.
We recommend that your paved area is kept free of leaves and general garden debris as this will keep it clean for longer. For best results clean your paved area with a small pressure washer (available in hardware stores i.e.Woodies) every six to twelve months, alternatively there are patio cleaning products available which may be easier to use but not quite as effective.