To Ditra or not to Ditra...

[HimediA]

The main point is assessing the deflection that is there.

If deflection is the issue that is something I can assess and make a judgement on (pint glass or no pint glass.)

But if that's the case why do people say that with a room my size (7/5m x 5.5m) I should consider using matting? What difference does the size make, assuming supporting brick piers are in every 1.5m or so under most floors surely the vertical deflection is going to be similar whether 2m, 20m or 200m?

 

[HimediA]

i think the ditra matting transfers the downward stresses to whatever is below it, and reduces the stress on the tiles somehow. it's not just lateral movement it counteracts, but vertical too. at least that's how i thought it worked.

Thanks John, but the engineer in me can't really see how a flexible 3mm membrane can really add much in the way of vertical shear strength. If the floor's solid then it's solid (well, within reason, you know what I mean), if it's really not solid then no thin plastic membrane in the world is going to add any significant deflection-preventing strength.

Of course I could just be a numpty.

 

[doug boardley]

dural or ditra is not there to take up the deflection, it's installed to combat lateral stresses.

 

[Aston]

hi himedia,

1, the delection (up and down movement) needs to be sorted. get this wrong and the height you've saved will seem irrelevant to the extra outlay of a newly tiled floor!!
2. the de-coupling membrane is to help prevent lateral movement (side to side) unfortunatey, all buildings move due to expansion and contraction through out the year, so if the floor is solid (no up and down movement) then id still put down a de-coupling membrane to counter balance the expansion and contraction.

the larger the area, the move need for a decoupling membrane.....

 

[HimediA]

dural or ditra is not there to take up the deflection, it's installed to combat lateral stresses.

Thanks Doug, that I can understand. But on a long-standing floor that has been significantly strengthened and really does feel darned solid, and with no underfloor heating or any significant underfloor moisture levels that are likely to bring about any lateral movement, I'm guessing that matting ain't really going to do a lot, except add to my bill and floor height...

Of course those cynics out there may now think I've just ignored all the advice and have gone with the answer I liked the sound of and could make fit. That really isn't the case. Promise.

If anyone out there can tell me why matting is going to make any significant difference to my floor then I'll lay it.

 

[rk ceramics]

You could use a AD1 additive to make the adhesive more flexible so no Ditra. cheers Richard

 

[HimediA]

Thanks AstonTiling, your 'everything moves throughout the year' point does make sense.

 

[Gazzer]

Probably a quicker way would be to chat with our Sponsor Dural Welcome

My point about deflection is just one issue. If the floor were free from deflection then I would still want a backer baord laid at least...I dont like tiling to wood...it will move. Seeing as you are laying stone then I would want a decoupler but the floor has to be solid. The size of the floor is quite large and as such will have more movent both ways than a similar constructed floor of a smaller size.
You may want to consider movement joints too....all that is discussed by clicking the Dural links on the side of the page here.

 

[Gazzer]

You could use a AD1 additive to make the adhesive more flexible so no Ditra. cheers Richard

Not if the adhesive is already polymer modified !!

 

[HimediA]

By that I'm assuming you mean labelled as a flexible adhesive (such as the Larsen one I have)?