Hi all
sorry about the long post but this should explain why a cement based adhesive should be used for porcelain tiles.
Ready mixed ceramic wall tile adhesives require moisture to be lost from the adhesive in order to allow the polymer binder to dry and forma ‘FILM’ capable of bonding both to the substrate and the tile.
A High proportion of large format tiles, typically 30cm x 30cm or greater are typically porcelain and as such, by definition the tiles have a water absorption of 0.5% or less. Therefore this would slow down the hard formation between a ready mixed ceramic wall tile adhesives and a porcelain tile. If the background is also of a low porosity or is in fact impervious to moisture, the ability of the adhesive to “dry out” would be severely hampered, bearing in mind that the only rational escape route available to this moisture would be via the open grout joints. The larger the tile, the fewer the joints, thus reducing the amount of open areas where moisture may escape. For this reason, Building Adhesives Ltd would recommend the use of cementitious based adhesives as a general rule to ensure the adhesive is capable of drying and setting beneath the tiles.
hope this helps bal tas 2