Ditra and anhyfix

[thickbed]

Hi all

Have a anhydrite floor starting next week and normally use ditra which I lay with cement based addy - Would it be possible to lay the ditra with a gypsum based addy instead? Obviously after sanding priming etc

Many thanks
Mike

 

[Just Rizzle]

thats the way i do it reduces your risk of ditra lifting makes sence its a no brainer m8

 

[thickbed]

does anyone else use this method as it makes sense to me but do schluter recommend this

 

[Just Rizzle]

read there tec page

 

[Ajax123]

Schluter can neither recomend nor otherwise as they have no test data to support one or the other. It would be up to the addy manufacturer to say if their gear sticks the mat down. My experience says yes...Anhyfix sticks down ditra

 

[Lee@emctiles]

With Alan on that, sold plenty of Anhyfix straight onto anhydrite screeds then used a decoupler, no issues.

 

[thickbed]

thanks for the replies and have just spoken to schluters technical and they say no to this and stick down with cement based saying it has a better bond this way-doesn't make sense - oh well thanks again

Mike

 

[thickbed]

as long as mc is below 2% which equates to approx. 82%rh on the box

 

[Ajax123]

as long as mc is below 2% which equates to approx. 82%rh on the box

And if you do that with a cement based addy at that moisture level it will fail within weeks... The sulphate laden moisture will react with the calcium aluminates in the cement forming ettringite which will cause the bond to break. An acrylic primer will not help because at this moisture level it will emulsify and further weaken the bond between the adhesive and the screed. There are NO cement based adhesives that I am aware of that can be used on anhydrite at moisture levels in excess of 75% rh or 0.5% moisture. 82% rh is way below 2% probably around 0.8%. 1.5% will give you an rh reading of 92%. In this instance schluter are offering bad advice. If you follow it... well...its up to you.

 

[thickbed]

Thanks ajax

Very interesting and makes sense.Really don't know how schluter can advise like this will give them another call tomorrow but in the meantime will use anhyfix to stick down with as long as rh is 85% or below on the hood and cement based on top

Thanks again ajax