Can you lay lay porcelain tiles on top of high density plaster board floor?

hi. I heard of people do that but personally i would add a 9mm ply screwed down to solid surface every 10cm2. that will be sound solution. Regards Pat.

absolutely not recommended, either 9mm ply or hardibacker on a wooden sub-floor is recommended then a flexible adhesive and grout must be used, to go slightly further and go belt and braces by using a decoupling membrane such as Ditra matting will help prolong the life of the flooring by helping to reduce the natural movement of the property from your tiles and adhesives.