SLATE on uhf and trav on fibre screed help!

[timlee77]

Hi just got a job need some advice just deciding weather i need ditra or something similar, im fixing slate to a fiber screed which has ufh pipes, should i use a ucoupling membrane or can i do without the screed will be bout 9 weeks old when i do the job? also i have another room to do on same screed type with 10mm trav do i need to use a membrane there ?? advice please fellas! ta :smilewinkgrin:

 

[White Room]

How thick is the screed......

 

[bugs183]

There is mixed views on this topic.
I always explain to the customer the benefits of an uncoupling membrane, and in a perfect world i'd Ditra both, especially the limestone floor, then leave it them to decide.
You'll get good deals on Ditra from Lilley Tile and Stone. Lilley Tile and Stone |.
Speak to Stu, he'll sort you out, worth getting a price for the adhesive off him too!

 

[Del W]

Id say ditra for both.

 

[timlee77]

Screed for slate is about 2 inch fiber screed ufh. its been down 7 weeks and will be 10 weeks when i tile. trav room not ufh. i forgot to mention the house is extension so im carrying existing slate opus from kitchen area (already tiled slate) on through extension kitchen not heated and seperate substraight so im putting movement joint in. what about hight of existing kitchen floor to hight of extension with ditra? there is another membrane called norcross permalayer Permalayer (1.2m width) its only 1.8mm thick ?

 

[Concrete guy]

I once had a very long conversation with Schluter systems technical department about Ditra matting and underfloor heating.

In summary these are the points made by Schluter themselves.

1. Whilst an uncoupling membrane is ideal with UFH it unfortunately acts as an insulation and makes the UFH less effective.

2. Due to the nature of UFH flexible adhesives are required, using flexible adhesive negates the purpose of Ditra matting as it goes quite a long way to actually stop the "uncoupling" mechanism itself.

Schluter Tech dept are extremely helpful people and will always make an effort to answer any queries.

Fundamentally Ditra matting was designed to deal with green screeds so contractors could fast track installations. It can also be used to negate or reduce expansion joints.

Most other applications have been made on the fly once people have been introduced to it.

In the early 90's I spent a lot of time pulling up floors that had been mistakenly tiled using this product as opposed to ply or panel reinforcement. I have no idea where retailers got the idea this stuff was a replacement for reinforcing floors, but they did and in huge numbers.

 

[bugs183]

Sorry ATS, i'm going to have to disagree there on Schluters advise.
I do believe that the mat plays a better role than flexible adhesives in the case of underfloor heating, and i'm surprised at Schluter for not saying 'we think it's better to have it'. I'll always recommend it in these cases as i know it works, i've seen enough jobs where 'flexible adhesives' fail.
It's a grey area if we're all honest, and i personally don't agree with their comments.

 

[Concrete guy]

Give them a call and put your case, I've always found them very open for discussion. Unlike some other manufacturers they are open to suggestions and will discuss the merits or possible problems of any use of their product.

 

[bugs183]

I always give anyone a ring if i have a problem or a query, and 9 out of ten times i find Schluter great, but i've had a couple of odd conversations, normally about underfloor heating, especially with wooden substrates and i felt that they weren't that on the ball.
Anyway, i'm still surprised at their answer and i'm still going to use Ditra!

 

[timlee77]

now very confused can someone advise i have hieght issues as extending existing kitchen floor (opus slate into extension ditra or no ditra that is the question??) :mad2::smilewinkgrin:

 

[bugs183]

Has the new screed been bought up to the exact height of the screed that is in the kitchen???
I'd certainly bridge those two floors with a strip of Ditra about 400mm wide, which would as Schluters comments above negate or reduce the joint you have between them. Then it's up to you if you want to Ditra. all of the new floor.
Ditra will bring it up about 5mm including the adhesive underneath, bear in mind the Norcross needs to be adhered to the floor as well.

 

[Concrete guy]

If I'm reading correctly this is 50mm sand/cement fibre reinforced screed with water UFH?

9 weeks curing is fine.

The heating should have been commissioned and run for a period of 28 days.

I'd then fit with a two part flexible adhesive directly to the (primed) screed.

As an aside, I wish firms would stop selling 10mm travertine for flooring, it's a wall tile at that thickness. Should be a minimum of 12mm for flooring.

 

[Concrete guy]

I always give anyone a ring if i have a problem or a query, and 9 out of ten times i find Schluter great, but i've had a couple of odd conversations, normally about underfloor heating, especially with wooden substrates and i felt that they weren't that on the ball.
Anyway, i'm still surprised at their answer and i'm still going to use Ditra!

The reason some of these conversations would come across as odd is due to the behavior of admixes in Flexi adhesives and their interaction with Ditra matting.

Ditra matting is designed to be used with a cement based adhesive (back in the day this was Ardex X7 or S16 if you needed rapid set). The flexible polymer admixed effectively stop the "uncoupling" or substantially reduces it. Therefore the purpose of fitting the Matting (to create an uncoupling) is actually negated by the materials you're using during the process. QED.

 

[bugs183]

The conversations were about an entirely different situation.
I'm just saying that sometimes, us guys on the our hands and knees using the products have a practical understand of the products in a way that the technical guys wouldn't see.
I'll agree to differ on this matter, but i will always recommend Ditra under tiles on any under floor heated screed, be it Anhydrite or Cement based, i've seen both of these screeds crack, ive seen stone floor fixed with flexible adhesive crack, but hand on heart (que phone call), i've not seen a crack in any of my uncoupled floor tiling jobs.

 

[Tony73]

agree with bugs183, we work with it every day. In my experience can say-ditra everywhere. Never had problem.