Large format tiles must be solid bed fixed in accordance with BS 5385. To ensure you’re achieving solid bed fixing on large format floor tiles, use a semi-pourable or pourable tile adhesive such as ARDEX X 325 PTB, ARDEX MICROTEC X 78 or ARDEX MICROTEC X 7001. To ensure you’re achieving solid bed fixing with a slump-free adhesive, ARDEX X 7or ARDEX MICROTEC X 77 for example, back buttering is usually required.