De-Coupling membrane would you insist

[peckers]

Hi there, Hope i have put this in the right place?

I was wondering if you would insist for a De-Coupling membrane to be used in this situation..

The floors have been recently screeded 6 weeks ago with sand and cement and the floor has under floor heating in stalled,
I have tested the floor with a damp meter and it is dry, so no worries there, the under floor heating is also not been turned on yet. the tiles to be laid on the floor are 300x300mm to be fixed with a suitable flexible adhesive and grout due to there being underfloor heating installed.
There are 3 floors to be tiled in 3 seperate rooms approx 20M2 each but the whole floor area which has been screeded is approx 450M2

At the moment there is no evidence of any shrinking or cracking in the sand cement screed which sometimes accurs while drying out,

My concerns are that due to the floor being new and the underfloor heating has not been turned on yet, that shrinkage or cracking may occur in the near future, so i have reccomended the use of a De-Coupling membrane to be installed so as if this does happen it will not affect the tiles,
The builder has said I have never had this done before and will not pay for it to be done!

So the question is this.
Would you insist on it being used ? and maybe loose the job because another tiler might not be quoting to install it..
Or would you tile strait onto the finished screeded floor and not worry ?

Many thanks for your comments and replies in advance:smilewinkgrin:

 

[DHTiling]

The heating needs to be turned on before tiling can commence....then cooled down ready for tiling....IMO a decoupling membrane will be the best option with new floors and ufh..

 

[DHTiling]

Read this>>> http://www.tilersforums.com/tiling-forum/14730-understanding-tiling-shift.html it will help you decide when and where..

 

[CJ]

Or use Bal Green screed adhesive, which is flexible.

As mentioned......the floor needs to be turned on and left on for 3 days.....then turned off and cooled right down.

 

[Ajax123]

Agree totally with Dave - Underfloor heating must be comissioned before tiling commences. This is to stabilise the screed which being cement based will shrink and possibly crack on heating.
Also there should be joints in the screed over that sort of area. The NHBC guidelines for sand cement screed bays is 15m2 or room size although I guess you would get away with 20m2 as long as the aspect ratio (length to width ratio) is not too great - look for no more than 2:1 with cement based screeds. There should be joints across the door thresholds as well. Additionally the underfloor heating guides usually say that there should be an isolation joint at the interface between independent heating zones. This is to take account of the potential for different thermal expansion and contraction in the screed due to different temperatures. If you tile before this is taken care of and the cracks occurr then the tiles will at best crack as well and at worst delaminate completely. A decoupling mat is one option but if you are worried about losing the job why not quote the customer two options - one with and one without and make sure he is aware of the implications of each. He can then make an informed decision as to which way he wants to go. Make sure you put the offers in writing.

 

[Ajax123]

Or use Bal Green screed adhesive, which is flexible.

As mentioned......the floor needs to be turned on and left on for 3 days.....then turned off and cooled right down.

Usual comissioning procedure for underfloor heating would be start flow at ambient (approx 25 degrees) for 3 days then increase temperature by 5 degrees per day up to its maximum temperature (often around 45 degrees) and then reduce by same 5 degrees per day to normal operating temperature - leave there for as long as you like to dry the screed (in this case appears already dry) then switch it off for a minimum of 72hours before tiling. - minimum total of 14 days (temperatures are water flow temperature not surface temperature) - If it is switched on too high then the screed will crack due to thermal shock so the gradual heat up is important.

 

[DHTiling]

Or use Bal Green screed adhesive, which is flexible.

As mentioned......the floor needs to be turned on and left on for 3 days.....then turned off and cooled right down.

Thats for green screeds col..not for preventing delamination of tiles due to stress.

 

[CJ]

Thats for green screeds col..not for preventing delamination of tiles due to stress.

Its wot i would be tempted to use as long as the heating has been run properly and cooled

 

[peckers]

Thanks all for your replies,
Which make or type of De coupling mat would you recommend ?

 

[diamondtiling]

A decoupling mat is one option but if you are worried about losing the job why not quote the customer two options - one with and one without and make sure he is aware of the implications of each. He can then make an informed decision as to which way he wants to go. Make sure you put the offers in writing.[/quote]

If he gives the customer these two options and the customer goes for the cheapest option is he not leaving himself open to problems if anything goes wrong? The customer could argue that he should have insisted on fixing the membrane because that was the correct path to follow, I am only saying this because of a similar thread warning of what might happen if things go to a small (or big) claims court.
I layed 400x400 trav over a screed containing water fed heating and there have been no problems, I did however fit room perimeter expansion joints that are hidden under the skirts and cupboards. The screed had been down for about 4 months but did have hairline cracks in it