Question for Ajax

[Gazzer]

Quote " traditional cement based screeds dry from the surface downwards, this means that you can monitor the drying out process over time as the RH value reduces week by week. Screeds normal drying rate is day per mm of depth as a general rule. Anhydrite screeds dry from the base upwards"


Question ...Why ?

 

[Peter]

Because the UFH is usually switched on by then. :lol:

 

[Ajax123]

Quote " traditional cement based screeds dry from the surface downwards, this means that you can monitor the drying out process over time as the RH value reduces week by week. Screeds normal drying rate is day per mm of depth as a general rule. Anhydrite screeds dry from the base upwards"


Question ...Why ?

where is the quote from.... Did I say it... Eek!! Must have been a wobbly moment.... It's not correct. All screeds dry by evaporation of moisture from the surface with the additional drying effect of cement hydration in the sand cement version. I hear the drying from the bottom upwards thing a lot. I think it is because of some of the misunderstandings that go on with screeds and how people measure and interpret results. In general what happens is that the surface of the screed begins to dry and this effect reduces the moisture in the top part of the screed. The body of the screed then wants to equilibrate as nature does not like unevenness. Thus " drawing moisture from the body of the screed. More moisture evaporates and more moisture is pulled through the screed in a bid to equilibrate. And so on... It's much easier to explain I pictures but I can't get them uploaded on here..... I do explain it in my tiling to anhydrite screeds course....

the relative rates of drying in a sand cement screed are much more linear than you see with anhydrite primarily because of surface texture and porosity. It is not however possible to measure either accurately along it's drying phase using anything other than direct moisture measurement eg oven dried sample or carbide bomb because all the other methods are affected by the moisture levels in the screed in relation to the atmospheric humidity.

 

[Mr Tiler]

so is the moisture drawn outward in all directions from the body of the screed or does it just go up to the surface? thanks

 

[Gazzer]

where is the quote from.... Did I say it... Eek!! Must have been a wobbly moment.... It's not correct. All screeds dry by evaporation of moisture from the surface with the additional drying effect of cement hydration in the sand cement version. I hear the drying from the bottom upwards thing a lot. I think it is because of some of the misunderstandings that go on with screeds and how people measure and interpret results. In general what happens is that the surface of the screed begins to dry and this effect reduces the moisture in the top part of the screed. The body of the screed then wants to equilibrate as nature does not like unevenness. Thus " drawing moisture from the body of the screed. More moisture evaporates and more moisture is pulled through the screed in a bid to equilibrate. And so on... It's much easier to explain I pictures but I can't get them uploaded on here..... I do explain it in my tiling to anhydrite screeds course....

the relative rates of drying in a sand cement screed are much more linear than you see with anhydrite primarily because of surface texture and porosity. It is not however possible to measure either accurately along it's drying phase using anything other than direct moisture measurement eg oven dried sample or carbide bomb because all the other methods are affected by the moisture levels in the screed in relation to the atmospheric humidity.

Screed Moisture Testing. | Churchill Flooring Blog

 

[Ajax123]

Well... Churchill flooring are no more...

 

[Ajax123]

so is the moisture drawn outward in all directions from the body of the screed or does it just go up to the surface? thanks

Essentially the moisture can onl escape from the surface of most screeds due to the presence of DPM's and edging strips. In some circumstances there can be tw way drying if no DPM is present under the screed e.g. First floor level. Some parts may dry more quickly due to uneven porosity which means the moisture will spread to a certain extent but as the part losing most moisture is the top the general direction of moisture is upwards.

 

[White Room]

where is the quote from.... Did I say it... Eek!! Must have been a wobbly moment.... It's not correct. All screeds dry by evaporation of moisture from the surface with the additional drying effect of cement hydration in the sand cement version. I hear the drying from the bottom upwards thing a lot. I think it is because of some of the misunderstandings that go on with screeds and how people measure and interpret results. In general what happens is that the surface of the screed begins to dry and this effect reduces the moisture in the top part of the screed. The body of the screed then wants to equilibrate as nature does not like unevenness. Thus " drawing moisture from the body of the screed. More moisture evaporates and more moisture is pulled through the screed in a bid to equilibrate. And so on... It's much easier to explain I pictures but I can't get them uploaded on here..... I do explain it in my tiling to anhydrite screeds course....

the relative rates of drying in a sand cement screed are much more linear than you see with anhydrite primarily because of surface texture and porosity. It is not however possible to measure either accurately along it's drying phase using anything other than direct moisture measurement eg oven dried sample or carbide bomb because all the other methods are affected by the moisture levels in the screed in relation to the atmospheric humidity.

Where does that happen....

 

[Ajax123]

haven't done one for a while. Looks like i might be doing one for kerakoll soon. Used to do them for BAL but not done one for a while. Did one for the forums up in Newcastle some time ago as well. If you want to organise a venue and send out invites I would be happy to do more.