Priming an old surface is sadly neglected before the start of your tiling projects. This is often overlooked due to the urgency of getting the tiling works underway. De-bonding of the adhesives from concrete sheets or concrete slabs easily occurs over time when there is some movement, heavy traffic, weighted items which causes pressure on the floor. If the sub floor is primed well, issues pertaining to de-bonding is never mentioned. We recommend the use of Mapei Primer G.