Anhydride screed

[Wolfie9878]

Morning guys

Quick one, I am starting a job next week, floor tiling a block of apartments, lafarge gyvlon screed. Can I avoid sanding and priming by using ditra stuck with a non cement based adhesive? If so which adhesive would you recommend?

If I can't avoid sanding what method should I use? Carbide sanding discs?

Thanks in advance

 

[Ajax123]

Sand it with a rotary STR sander and 60 grit paper followed by vacuuming. You can still stick ditra down with non cement adhesive but this is nothing to do with sanding. You are sanding to remove surface contamination and loose friable materials from the screed surface.

Floor Scarifier 110v

This is the type of machine

 

[Wolfie9878]

Cheers for clearing that up.

Next question-

I'm being asked to tile the screeds before they are fully cured to meet deadlines (it's a national builder) is it possible to ditra and will this allow the screed to dry without affecting tiles, grout etc?

 

[Ajax123]

The screed should be below 75%relative humidity when measured with a hair hygrometer in order to tile successfully with a cement based adhesive. Schluter do say that you can lay the uncoupling membranes at 2% moisture which would be around 95 to 98 % rh but they do not I've any firm guidance on how this might be acheived as the adhesive manufacturers all say 75% or less.

The alternative is to use a gypsum based adhesive. Most of these can be used primerless at below 85% relative humidity although you need to be careful not to abuse this. Bare in mind also that the screed can be aggressively force dried after just seven days so you can get it dry pretty quickly. The only issue with gypsum is that there is some extra cost up front but to be fair of all the nationals I have dealt with they have felt that this is a small price to pay in the overall scheme of things compar to cost of delays or of failures. Bae in mind that evenif itis more expensive they will still try and squeeze your prices so stand firm.

 

[Wolfie9878]

Nice one Ajax, every day is a school day!