Tiling over clay tiles.

[MalcyB]

Hi all.
I hope you will be able to give me some advice on this .
A friend has asked me to tile her kitchen floor. They already have ceramic tiles down which her husband laid many years ago. One or two have come loose so they are all going to be taken up.
I am concerned about tiling on top due to the possibility of damp/moisture getting trapped. As far as they know there is no DPM. They haven't noticed any signs of damp.
Would laying a porous tile be best if so, which adhesive and preparation would be best?
Thanks in advance for any information
Malc

 

[Albert]

Hi all.
I hope you will be able to give me some advice on this .
A friend has asked me to tile her kitchen floor. They already have ceramic tiles down which her husband laid many years ago. One or two have come loose so they are all going to be taken up.
I am concerned about tiling on top due to the possibility of damp/moisture getting trapped. As far as they know there is no DPM. They haven't noticed any signs of damp.
Would laying a porous tile be best if so, which adhesive and preparation would be best?
Thanks in advance for any information
Malc

If there isnt a dpm then you need to install one, you can do this in several ways
the easiest one i have used was an epoxy, just apply with a roller and leave
to dry

 

[MalcyB]

Can you recommend one?
What will happen if there is moisture under/in the clay tiles?

 

[Bond]

If you use a porous tile, trapped moisture will move slowly and evaporate from the surface, possibly causing discolouration due to moisture and salts. As noted above, tank/waterproof floor, may be advisable to apply anti-sulphate first to prevent the migration of salts to the surface. And check position of dpc to any abutting walls, as trapped moisture may transfer there also.

 

[MalcyB]

Right, looks like it's not going to be straight forward then.
Can you recommend which products would be best to do this?
Thanks for the advice.
Malc

 

[Bond]

There are so many products on the market that will deal with rising damp in a concrete slab and qualify as a damp proof membrane. Brush or roller applied liquid -epoxy resin or cementitious coatings are among the easiest to apply .
If you system requires a anti-sulphate have a look at Hey di antisulphate from Sovereign Chemicals.

 

[MalcyB]

Sorry, I think we might be on different lines here? Correct me if I am wrong.
The building is over 100 years old.
They have ceramic tiles laid on top of original clay tiles, under that we don't know what there is?
Do I still need to treat with antisulphate stuff and tank with epoxy?
Sorry if how I put it down sounded different.

 

[Bond]

Sorry, I think we might be on different lines here? Correct me if I am wrong.
The building is over 100 years old.
They have ceramic tiles laid on top of original clay tiles, under that we don't know what there is?
Do I still need to treat with antisulphate stuff and tank with epoxy?
Sorry if how I put it down sounded different.

When you remove all the tiles, on inspection the concrete slab does not have a insitu damp proof membrane, then continue,as above.

 

[MalcyB]

The idea was to leave the clay tiles down as they are solid and tile over, but if it would be better to remove them all and see what is underneath then that is what will have to happen.

 

[Bond]

You can check the moisture content of the concrete slab, by drilling into the slab at various depths through the grout line, using probes connected to a conductance type moisture meter. If the readings are in the high- red zone that may indicate the absence off or an ineffective damp proof membrane. ( you should be able to hire moisture meter etc.). If you do this use a new masonry drill bit -at low speed. Take readings in various places especially close to external walls. You could also try, taping small sections of polythene to the clay tiled floor, observe over a couple of days, if visible moisture is present then you have a damp problem.