We are in the middle of renovating our 1400s cottage and need to make a decision on how we are going to lay our limestone slabs. The existing floors differ across the house, one area is 4 inches of concrete straight onto earth, another area is deeper concrete and the other area is 60s build concrete floor. There are no DPMs anywhere. A water based latex has been used across the floors in an attempt to level areas ready for tiling.
When we originally moved into house there were ceramic tiles across the whole ground floor and when we lifted them they didn’t come up easily (SDS drill needed!) and there were no signs of moisture.
During our renovation we have ensured that breathable materials have been installed, removing cement tanking on ground floor that was trapping in moisture, and installing thermal lime plaster to external walls. The 60s part of the house is mostly dot and dab.
Our tiler wants to lay ditra mat across the concrete floors and then tile with their normal Ultra adhesive. He says the mat has grooves in the bottom which allows moisture to escape by sending it out to the walls. Because the house has a number of generations of concrete slabs, there is a greater chance of movement and consequent damage to the limestone we lay on top, so the ditra mat will protect from this. However I am concerned about laying a totally impermeable material when everything we have learnt about old houses says materials should be allowed to breathe. I always thought concrete was impermeable but have learnt this isn’t the case and it does allow moisture through. In fact in the room with the 4 inches of concrete on earth, there are visible patches where materials have been stored on the floor. Moisture meter confirms these are areas of higher moisture content.
Moisture content varies from 8-20% across the floors, with the highest readings at the room edges.
The alternative as I see it is using a breathable adhesive like Kerakoll H40 and accompanying breathable grout, straight onto the concrete (which kerakoll says is suitable substrate), and not sealing the tiles. This brings the risk of cracking and also salts coming through stone?
Am I over-worrying about the need for breathability when the old ceramic tiles were there for years without any obvious issue?
We have spent a fortune on the limestone and will be another small fortune to have it laid, so don’t want to make the wrong decision.
Any guidance would be gratefully received.
When we originally moved into house there were ceramic tiles across the whole ground floor and when we lifted them they didn’t come up easily (SDS drill needed!) and there were no signs of moisture.
During our renovation we have ensured that breathable materials have been installed, removing cement tanking on ground floor that was trapping in moisture, and installing thermal lime plaster to external walls. The 60s part of the house is mostly dot and dab.
Our tiler wants to lay ditra mat across the concrete floors and then tile with their normal Ultra adhesive. He says the mat has grooves in the bottom which allows moisture to escape by sending it out to the walls. Because the house has a number of generations of concrete slabs, there is a greater chance of movement and consequent damage to the limestone we lay on top, so the ditra mat will protect from this. However I am concerned about laying a totally impermeable material when everything we have learnt about old houses says materials should be allowed to breathe. I always thought concrete was impermeable but have learnt this isn’t the case and it does allow moisture through. In fact in the room with the 4 inches of concrete on earth, there are visible patches where materials have been stored on the floor. Moisture meter confirms these are areas of higher moisture content.
Moisture content varies from 8-20% across the floors, with the highest readings at the room edges.
The alternative as I see it is using a breathable adhesive like Kerakoll H40 and accompanying breathable grout, straight onto the concrete (which kerakoll says is suitable substrate), and not sealing the tiles. This brings the risk of cracking and also salts coming through stone?
Am I over-worrying about the need for breathability when the old ceramic tiles were there for years without any obvious issue?
We have spent a fortune on the limestone and will be another small fortune to have it laid, so don’t want to make the wrong decision.
Any guidance would be gratefully received.
