tiing on green screed

[Ajax123]

imo you never tile on a screed until it is fully dry. ditra is just hiding the problem that may occur.
The fluting as you say may allow a small amount of air flow but with the condensation that will
accur under the matting the screed will never dry properly.

Ditra matting as with most other plastics is not opaque to the passage of moisture. Also the fabric of the building will allow the passage of moisture. Ditra helps to control the rate at which moisture migrates to the surface. This will happen very slowly and the screed will eventually dry regardless of what is on top. The entrapment of moisture is not its primary function. It is designed to allow for differential movement between the screed and the adhesive such that the interfaces between the elements are not disrupted.

i do agree that the screed should be properly dry prior to tiling. However if it is not properly dried there are mechanisms to cope with the situation.

 

[cam_low]

cracking thread this [MENTION=12267]Ajax123[/MENTION] 😉

 

[Ajax123]

I get frustrated when I see people making statements. Know t be wrong. I can't help myself ... I must type .... 🙂

 

[wakes]

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.

 

[White Room]

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.

Trouble is most customer want it done now and don't want the wait, theres allways Bal green screed adhesive as well.

 

[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.