# Measuring Moisture Content of 75mm Sand:Cement Screed



## BMD (9 Aug 2011)

Hi,

I am looking for some advice on how to measure the moisture content of floors before laying tiles or engineered floors.

I want to know how to measure the moisture content and what figures I should be looking for?

Also what are typical recommended drying times for 75mm sand:cement screeds (with UFH)

Any advice would be appreciated


----------



## Docarch (9 Aug 2011)

All I can offer is a rule of thumb of a drying time of 1mm per day - so 75mm - allow 75 days.  

To clients, I always suggest getting the (written) advice of the tile/timber flooring supplier as to the appropriate moisture content required for the selected product.  

Any good tiler or timber floor installer/layer should have a good moisture meter for checking the moisture content.  Alternatively, afaik, they can be hired.


----------



## BMD (9 Aug 2011)

Thanks, what should the moisture level in the screed be? Is it measured as % RH?


----------



## Docarch (10 Aug 2011)

'Fraid I cant really answer that one BMD - sorry.  That's why I would suggest getting recommended moisture (max) levels from tile or timber flooring suppliers.


----------



## Leo (10 Aug 2011)

BMD said:


> I want to know how to measure the moisture content and what figures I should be looking for?


 
Buy or rent a moisture meter. Refer to the specs of your chosen flooring to see what's acceptable.
Leo


----------



## onq (10 Aug 2011)

Some interesting and relevant information here.

http://www.pci.uk.com/en/Tilingadvice/HowToGuides/TilingOntoConcrete/Pages/default.aspx


ONQ.  

[broken link removed]  

All advice on AAM is remote from the situation and cannot be relied upon        as a defence or support - in and of itself - should legal action   be      taken.
Competent legal and building professionals should be asked to advise in        Real Life with rights to inspect and issue reports on the matters   at      hand.


----------



## BMD (18 Aug 2011)

Does the 1mm a day change if you have the UFH on?


----------



## onq (18 Aug 2011)

Drying out floors too quickly can result in crazing and cracking. Most concrete screeds generate some level of heat, the more cement in the mix, the more heat IIRC - the challenge is to keep it cool.
However other screeds may not rely on cement chemical reactions and you need to address this with your supplier of screeds as mentioned by Leo and Docarch above.

Don't confuse moisture content of flooring with "allowing the screed to dry out" when you're talking to people.
Be careful of tilers who do not install tiles on full bed tiles. Leaving  hollows can cause tiles to crack and water to lodge there if there's a  spill.

Be aware of problems with dusting of surfaces prior to laying tiles, because if not your tiles will lift and you'll have to re-do the whole floor.

Did you read the link I posted?



*Allow  at least 6 weeks for new concrete to cure with air drying before  applying a screed or directly bedded materials.This time may have to be  extended in wet weather (refer to BS 5385: Part 3: 14.2.3 for curing  standards). If this is not followed then when the concrete shrinks, the  bond between the adhesive and the concrete will be broken. *
If  early fixing is required for fast-track projects, use an external  reinforced decoupling matting system such as a Shlüter system, along  with a polymer modified adhesive such as PCI’s Tilefast 6 RapidFlex.
For  vinyl sheeting, where a 150mm-thick concrete slab is laid on to a  suitable DPM (Damp Proof Membrane) is used, it can take up to a year to  dry.
With new build projects, there  is usually a damp proof membrane below the concrete which will prevent  the moisture rising but if not, consider using a surface membrane such  as SDPM (Surface Damp Proof Membrane).
Use a primer, such as PCI’s Primer G, if the concrete is dusting or the porosity is high.

There is a sense that you don't want to accept the advice being posted, which appears to offer best practice.
Concrete takes time to complete its process and you'll have to go with the flow on this.


ONQ.  

[broken link removed]  

All advice on AAM is remote from the situation and cannot be relied upon         as a defence or support - in and of itself - should legal action    be      taken.
Competent legal and building professionals should be asked to advise in         Real Life with rights to inspect and issue reports on the matters    at      hand.


----------



## BMD (18 Aug 2011)

No problem accepting advice...none of the posts I read dealt with UFH so I just wanted to confirm. Most the research I have done on screed drying times have also neglected the impact of UFH (good or bad).

I read the link that you posted but didn't find it great unfortunately. To be honest, I think 6 weeks to cure new concrete is not sufficient and isn't something that I would recommend. 

All the same I appreciate your advice and as usual I accept that this is only your opinion and is non-binding


----------



## onq (18 Aug 2011)

I'll assume you noticed the third point -

_"For  vinyl sheeting, where *a 150mm-thick concrete slab is laid on to a   suitable DPM (Damp Proof Membrane) is used, it can take up to a year to   dry*."_

Also that the first point was not suggesting "6 weeks" as a maximum drying period, or even a standard period, but as a *minimum period*.

ONQ.  

[broken link removed]  

All advice on AAM is remote from the situation and cannot be relied upon          as a defence or support - in and of itself - should legal  action    be      taken.
Competent legal and building professionals should be asked to advise in          Real Life with rights to inspect and issue reports on the  matters    at      hand.


----------



## BMD (19 Aug 2011)

My post didn't concern vinyl sheeting, therefore although I did note the third point, it is not relevant in this case.

I feel that a *minimum** of 6 weeks* is not long enough and is not good practice, therefore I would not encourage this.


----------



## onq (19 Aug 2011)

The third point is very relevant if you're interested in how long six inches of concrete takes to fully dry out.

Straw man argument - I didn't and don't encourage working to a minimum.

ONQ.  

[broken link removed]  

All advice on AAM is remote from the situation and cannot be relied upon           as a defence or support - in and of itself - should legal   action    be      taken.
Competent legal and building professionals should be asked to advise in           Real Life with rights to inspect and issue reports on the   matters    at      hand.


----------

