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

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..

Read this>>> http://www.tilersforums.co.uk/tiling...ing-shift.html it will help you decide when and where..

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.

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.

Originally Posted by 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.

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.

Originally Posted by 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.

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

Originally Posted by Dave

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

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

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

2 types that i recommend are Ditra or Durabase Ci....

Originally Posted by 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.

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[/quote]

You are quite correct in that if 2 options are offered and one is incorrect then the tiler could be deemed as negligent. In this instance however I don't beleive that situation exists because both options meet the requirements of the relevent standards. The option without the Ditra would be minimum standard and the offer including Ditra becomes an enhanced offer.

I think the thread you are talking about involves waivers of guarantee. This is a different situation because it involves asking a customer to waive their rights so that you can do the job knowing what you are doing is wrong e.g. Customer asks you to put the tiles down and the moisture test says screed is still too wet. You install the tiles at the customers request and say you won't guarantee the installation. If you do this you are negligent as you are deemed as being a supplier of a specialist product or service and as such should demonstrate due dilligence in you proffession. If this happens and you are sued through the courts you will lose. The laws on waiver are pretty damned complicated and basically encourage people to do the job right in the first place.

On the basis that the UFH has not been commissioned you must tell the customer that his screed is simply not ready for tiles as yet. Additionally joints in the screed are an important feature of the flooring mechanism. I guess the two options are Ditra and tile now or no ditra and tile later when its ready.

Your point is well made though

if I had a slightest doubt, I'd insist! (short and sweet lol!)

Originally Posted by doug boardley

if I had a slightest doubt, I'd insist! (short and sweet lol!)

Think I probably agree. If not and it goes wrong it will always bite you in the a*se. I think it is important if you are having to compete though to offer the two options but spin it in such a way that there is only one option.

sort of "yes mr customer. I could easily do it for that really cheap price but I don't do shoddy work and don't want to give you all these problems...list of problems.... followed by sales pitch as to the right way" and all that....

I have read everyones replys to this thread, and i agree that a proffesional tiler should submit the best procedure and products to allow him to do the tiling job in hand the correct way. This ensuring that the customer gets a long lasting proffesional finished product. And that the tiler can sleep at night knowing that he has done everything to the letter and dotted the Is and crossed the Ts or so to speak.
As previously mentioned i have tested the floor with a damp meter and it is dry, The customer has agreed to have the underfloor heating commisioned and run before tiling commences.
How ever the customer does not want the expense of a De-coupling membrane being installed.
My concern is that even though the underfloor heating is being run and commisioned and that it is dry, that it is still relatively new. And it could possibly crack in the not so distant future, My problem is that i am pricing against another tiler who is not offering the de coupling membrane installation and he is therefore cheaper, I have argued that my expertise and knowledge of this situation is worth taking into consideration.
But I suppose all the customer is concerned about is the expense now rather then the expense and problems that can accur later on.
If the floor had been down for a considerable time then i would not be concerned and would tile on it with out a de-coupling membrane as I have done this in the past and never ever had a problem. although i have always ensured that that there is addequate expansion around the floor pirimeters and in the doorways!
I also understand that if i give them the cheaper option of no de-coupling membrane and they sign a disclaimer that if a problem does accur then they could still win in court, if it went that far.
So i am now thinking that i should show them evidence of what could happen at a later date if a de-coupling membrane is not used.
Does anyone know where i can down load a picture of this???
And if this doesent change there mind then they are not worthy to recieve my expertise and knowledge, and Good luck to the other tiler

Many thanks for everyones replies....

2 threads you might get some info from...

http://www.tilersforums.co.uk/tiling...ing-shift.html


http://www.tilersforums.co.uk/tile-a...rol-joint.html

Does anyone know where i can down load a picture of this???


Many thanks for everyones replies....[/quote]

Not sure if this helps but this is a sand cement screed that did not have the UFH comissioned prior to floor covering being placed. If this happens under your tiles bang they go. If Ditra used the tiules are separate from the screed so reduce the risk very significantly. Not sure if I uploaded it right cos not a computer whiz - I know about screeds though....

That screed dos'nt look deep enough, the pipes are visible

Originally Posted by whitebeam

That screed dos'nt look deep enough, the pipes are visible

Pipes visible cos big hole in screed ...

seriously though the pic is a bit deceptive - was actually 40mm cover to the pipes which should be enough - 65mm overall depth reinforced class B screed.
Is quite an old pic - probably 10 years plus now. We repaired this one with an Epoxy resin after filling in the holes. (there were several failure sites like this one. Failure was due to thermal shock though. Vynil flooring was laid with primer and leveller (removed prior to pic) and then the heating was switched on at relatively high temp. Screed cracked - flooring failed. IMO if Ditra had been used and tile laid over the top then tiles separate from screed so screed movement not a major issue.

Ditra would have kept some moisture there.

Originally Posted by whitebeam

Ditra would have kept some moisture there.

It would also have acted as a vapour stbilisation layer allowing the screed to continue drying allbeit very slowly. The moisture would not have been disruptive to the tiles cos they would be separate. As it happens in this case I don't know if the screed was still damp or not.

me personally depends on the tile being fixed if it is ceramics i would use a flexible adhesive grout etc but id place an expansion joint round the perimetre of the room

if using natural stone trav or limestone i would insist on using an un coupling membrane