Ditra Matting On Part Of A Floor

[James Green]

Hi,

We have a 55 square metre kitchen that we want to tile with 80cm x 50cm limestone tiles. We have NO UFH.

80% of the room is a newly screeded floor (extension) which is perfectly level (to within the tolerance of an 8 foot level placed in various places). The screed is dry having been down for 3 months.

Our challenge is the existing screeded area (20% of the floor and in one “strip”) is not level and runs out to approximately 6mm higher at one end of the room and 2mm lower at the other end when compared to the new screed.

We want to avoid having to pour self levelling compound over the whole area so one solution we have is to lay ditra matting on the new screeded area on a 6mm adhesive bed to raise the level by approximately 6mm. We can then use self levelling compound on the old screeded area to bring it up to the level of the ditra – and end up with a level surface.

What are the opinions out there on this solution? Is self levelling the whole area the only way to go? I looked at the ditra and it seems to have very little vertical flex.

Thanks for taking the time to read this.

James

 

[One Day]

The correct way (and safest/best use of funds) would be to ditra the lot but build up the adhesive bed a little on the new part. I have to say, an 8mm deviation on that area is tiny. Most of us would be overjoyed to have a floor so good! You can safely build up to 10mm on ditra btw.

 

[One Day]

You should really install a fixed expansion joint at the junction of the two floors AND use ditra.

 

[James Green]

You should really install a fixed expansion joint at the junction of the two floors AND use ditra.

Thank you for the quick reply. The approach you suggest makes perfect sense. My only reservation is how easy it is to build up the level using adhesive. Could I apply a 6mm bed of adhesive on the new floor (where the floor is out by 6mm), let this adhesive go off, and then lay the ditra on this (filling in the grooves of the gone off bed). This way using different notched trowels I can get a broadly level base before applying the ditra.

Could I ask what your thoughts are to the method of part ditra on the new screed and self level old screed to meet the the ditra? Would you be concerned about the tiles that are part on the ditra and part on the self levelled? Perhaps the flexible adhesive (webers) would cater for this movement?

 

[James Green]

The correct way (and safest/best use of funds) would be to ditra the lot but build up the adhesive bed a little on the new part. I have to say, an 8mm deviation on that area is tiny. Most of us would be overjoyed to have a floor so good! You can safely build up to 10mm on ditra btw.

Just to confirm - would you build up the adhesive bed underneath or on top of the Ditra?

 

[Flintstone]

6mm is nothing! Just build up a little where needed.

 

[One Day]

Just to confirm - would you build up the adhesive bed underneath or on top of the Ditra?

If you can do it underneath, it would be preferable (technically speaking). As a pro though, for speed and simplicity I'd just bed up on top - no more than 10mm or the ditra fails to work as designed.

The reason for covering the whole floor is to reduce the risk of lateral movement causing fractures. That risk is massively increased when 2 substrates meet. Flexible adhesive and slc will not accommodate this.
For example- ditra will accommodate a massive amount of movement - we're talking >10mm. Adhesive etc when it says "flexible" will be <0.5mm before failure (depending on manufacturer + spec etc)

Watch the following for a good grasp of what's involved: Schlüter®-DITRA 25 | Video | Schlüter-Systems
(bottom video especially)

 

[SJPurdy]

Hi,


We want to avoid having to pour self levelling compound over the whole area so one solution we have is to lay ditra matting on the new screeded area on a 6mm adhesive bed to raise the level by approximately 6mm. We can then use self levelling compound on the old screeded area to bring it up to the level of the ditra – and end up with a level surface.

 

[SJPurdy]

We want to avoid having to pour self levelling compound over the whole area so one solution we have is to lay ditra matting on the new screeded area on a 6mm adhesive bed to raise the level by approximately 6mm. We can then use self levelling compound on the old screeded area to bring it up to the level of the ditra – and end up with a level surface.

Why not SLC all the low area? You seem to be looking at options to raise the floor by that amount anyway.

You should not bed up under Ditra (as I understand it! - that is certainly an instruction with the Dural matting which is similar fleeced backed decoupling membrane (they recommend max. 4mm notched trowel)). I therefore recommend you confirm this with Schluter web site instructions (or tech help line). If you want to use Ditra then SLC under it leaving sufficient depth for the DItra on a thin adhesive bed.

 

[James Green]

Hi,

My only reservation with SLC is we've not done it before so a bit unsure how difficult this is on an area so large. But this with ditra on top is my preferred option based on the comments so far.

Would you mix a 25kg bag of SLC at a time and pour /spread with a spiked roller? Also would you cover the whole area say 3mm and then top up with another 3mm or lay 6mm of it in sections? My danger is the SLC dries before we have time to mix and pour the 12 bags needed.