All valid points above........ just make sure the grout is suitable for 1mm grout lines. Most only go down to 2 or 3mm. I've used the one by Mapie a few times and it works a treat.
Tiles turned out to be 300x50 slate. I only had to tile just over 5sqm, but due to other trades onsite it took 2 days. Also, due to the size of the tile I had to make about 300cuts!!! Very slow (but enjoyable) process. As requested by the customer I did not put in a grout joint. Strangely enough I was on the platform of Paddington station at the weekend, I walked passed McDonalds and saw the very same tile (no grout). It goes without saying that I did advise about having no grout, but as they say ‘The customer is always right’ Cheers for your help. Sean