...is suitable for 500 x 500 porcelain onto solid floor, 80% sand/cement 20% existing ceramics? I was thinking Keraquick or Adesilex P4 but nor sure if either of these are ok onto the existing ceramics.

Hi Rich..

Keraquick is suitable... are the existing tiles well secured..?

Thanks. Yes they are well secured. Do they need abrading first or can I go straight onto them, once I've cleaned the surface? Is the Keraquick ok with a large format trowel and if so, what sort of coverage can I expect?

I'd go with the keraquick too,the S1 properties stick really well.You'll need to make sure you have the surface degreased well and if its a glazed ceramic i'd be tempted to graze the surface too.any loose tiles get em out and fill hole or re stick the tile down

trowel wise i'd be comfortable with a 10 or 12mm,if your floors is not level you may need to level it .

I like Keraflex for Porcelain - especially for tiling onto old ceramic tiles and with 500x500 'large' format.

its use keraquick with the latex liquid u get for it and also 10mm trowel

Having spoke to mapei regarding this in the past I can say that for floors it is recomeded that you use the latex plus admix but kerraquick alone should be sufficient for walls.

Just be sure to degrease the existing tile surface, perhaps use some sugar soap or something. If you are happy to spend a little extra on prep you could use 'grimex' an intensive cleaning solution by LTP.