tiing on green screed

[wakes]

exposure over several years then some gypsum swelling can occur but it still remains hard. It does not like to be damp primarily because when itis damp it is almost impossible to get a cement based compound to stick to it

Read more: http://www.tilersforums.com/tiling-forum/64155-tiing-green-screed.html#ixzz2EDaXyTuS

Enough said on a green screed as above said by the technical expert!!

 

[Ajax123]

If a screed is fully dry as it should be prior to tiling the there is no need to use all
that expensive ditra. my statement is is not wrong!!! Tile on a fully dry screed and you should not have
a problem. and no extra cost to you or the customer.

Your statement about screed needing air to breath and it falling apart over time due to moisture is wrong.... Sorry but it simply is.

Some things to consider

the need for ditra or any other form of uncoupling depends on many factors other than the moisture content of the screed. You are right that the screed should be properly dry... I will not argue with that. Unfortunately time constraints on a project dictTe it might not be. technical constraints often mean it wont be properly tested so often the tiler wont know one way or theother. additionally the screed should also be sound, clean and free from other defects likely to cause a failure of adhesion. They should be fully compacted, correctly laid with joints at appropriate points and of the correct mix ratios and depth. Problem is they do not always (maybe read often instead of always) meet these requirements and uncoupling is a means of overcoming some of these issues. Also the need for uncoupling is dependent on the tile type and joint configuration and whether the screed is heated or unheated. BS 5385 says that natural stone tiles on heated screeds should be uncoupled. Ditra satisfies this requirement. Tile bay sizes can be effectively increased by using uncoupling. Cement screeds are notoriously unstable whether suitably dry or not....bear in mind they will never be totally dry .... And whilst moisture is present cement will continue to hydrate and hydration causes shrinkage. This places horizontal stresses on the screed matrix and in the long term causes cracking. Ditra will overcome this.

Where I do get very frustrated with the use of uncoupling membranes is the insistence that they are a requirement on anhydrite screeds. For various reasons there is far less of a need with these type of screeds especially if you use gypsum based tile adhesives....(awaits the fall out)

whichever way you look at it whilst they may not be essential in all cases they satisfy a need within the market to overcome the issues that are often beyond the control of the tiler and really let us say a client is building a 100m2 house. This is likely to cost well over a hundred grand ... The tiles alone can cost ten grand. Is an outlay of another 600quid for ditra really going to break the bank....

- - - Updated - - -

exposure over several years then some gypsum swelling can occur but it still remains hard. It does not like to be damp primarily because when itis damp it is almost impossible to get a cement based compound to stick to it

Read more: http://www.tilersforums.com/tiling-forum/64155-tiing-green-screed.html#ixzz2EDaXyTuS

Enough said on a green screed as above said by the technical expert!!

would not use green screed adhesive on anhydrite screed....

 

[Ajax123]

hi lads is there a adesive that can be used on a greed screed thats suitable for stone

Of course none of the debate answers the question..... The answer is yes there is but it may not tobe the most appropriate method of fixing.

 

[wakes]

Ajax i can't quite see where i said it would fall apart??? All i said was in a shell I dont agree
with tiling on a screed that isnt fully dry. thank you for your scientific side to the question.

At least we agree that tiling on a green(not fully dry) screed isnt the way forward but according
to your very indepth report it is possible.

May i say i wont't be using ditra on a screed floor just for the sake of a few days to tile
on a sound floor that doesnt require any extra work!!!

 

[Ajax123]

i disagree there wingn. if its a green screed and not fully dry then covering with ditra
the screed may never dry as screed needs air to breath and dry so will break up over time.

Just here mate.

 

[bugs183]

I've just been on the Schluter Substrates course and they certainly recommend the use of Ditra on green cement screeds, and say themselves that the amount of moisture trapped in the screed is not huge as the chemical reaction uses a good percentage up, and that the residual will escape through the flutings.
yes it does incuur extra cost but if on a limited time scale then this would save a project weeks of delay.

 

[huckin]

ok thanks for your comments i knew about bal green screed but thats no good with travatine as is only avaible in grey. i think i will tell the customer im not willing to do the job until is dry.

 

[Peter]

If its travertine you're better laying with Ditra anyway, regardless of how long the screed has been down.

 

[afright]

Have used Bal green screed a few times, but just a question would you use green screed adhesive to stick the ditra down if not what adhesive could you use on a green screed in conjunction with the ditra?