ᐅ From what point is it no longer possible for a screed to cup?
Created on: 23 Sep 2016 11:03
A
andimann
Hello everyone,
Our screed (fiber-reinforced cement screed) has been installed for 4 weeks now, and since yesterday the heating is finally running and gradually warming up.
From when is there no longer a risk that the screed will crack during drying? After 4 weeks it is considered cured. Can we now use dehumidifiers to support the drying process?
Background:
We have two basement rooms without windows (they will later be ventilated via controlled residential ventilation, which is not running yet). Naturally, drying through ventilation is difficult there (currently constantly 90% humidity), and I would like to assist the process a bit.
Our site manager is constantly holding me back and would prefer to leave the screed for at least 12 weeks...
Thanks and best regards,
Andreas
Our screed (fiber-reinforced cement screed) has been installed for 4 weeks now, and since yesterday the heating is finally running and gradually warming up.
From when is there no longer a risk that the screed will crack during drying? After 4 weeks it is considered cured. Can we now use dehumidifiers to support the drying process?
Background:
We have two basement rooms without windows (they will later be ventilated via controlled residential ventilation, which is not running yet). Naturally, drying through ventilation is difficult there (currently constantly 90% humidity), and I would like to assist the process a bit.
Our site manager is constantly holding me back and would prefer to leave the screed for at least 12 weeks...
Thanks and best regards,
Andreas
Hello "andimann".
Cupping tends to occur more frequently in cement screeds during the drying phase.
The question of how long a cement screed can cup cannot be answered satisfactorily on its own. Why? Because it depends on the surrounding drying conditions.
For example, if the screed is kept for over one year at 90% relative humidity, it would not dry and therefore would not cup.
In fact, cupping occurs to a greater or lesser extent with every cement screed as soon as it begins to dry.
This issue should not be overemphasized.
Screeds (if it is a cement-based heated screed) should be gradually heated after 21 days. This process is known as "functional heating." Intensive ventilation by opening windows partially for several hours is absolutely necessary (otherwise, where should the water go?).
If the cement screed cannot be heated due to the building design, then after the third day, intensive ventilation should also be used to promote drying.
In the case you described, there are no window openings.
Then forced drying must be used instead. For several rooms with only one condensate dehumidifier, but with many fans (to ensure good air circulation inside and between rooms).
---------------------------------------
Regards, KlaRa
Cupping tends to occur more frequently in cement screeds during the drying phase.
The question of how long a cement screed can cup cannot be answered satisfactorily on its own. Why? Because it depends on the surrounding drying conditions.
For example, if the screed is kept for over one year at 90% relative humidity, it would not dry and therefore would not cup.
In fact, cupping occurs to a greater or lesser extent with every cement screed as soon as it begins to dry.
This issue should not be overemphasized.
Screeds (if it is a cement-based heated screed) should be gradually heated after 21 days. This process is known as "functional heating." Intensive ventilation by opening windows partially for several hours is absolutely necessary (otherwise, where should the water go?).
If the cement screed cannot be heated due to the building design, then after the third day, intensive ventilation should also be used to promote drying.
In the case you described, there are no window openings.
Then forced drying must be used instead. For several rooms with only one condensate dehumidifier, but with many fans (to ensure good air circulation inside and between rooms).
---------------------------------------
Regards, KlaRa
Hello KlaTa,
thank you for your reply. We have underfloor heating almost throughout the basement, so the screed in one of the two windowless basement rooms is now being heated. The second windowless basement room is the utility room, which has no heating.
In both rooms, there are dehumidifiers running, and the humidity level hovers around 65-75% at about 22°C (72°F). The dehumidifiers do not run continuously (their tanks fill up after about 5-6 hours), so I think the drying process is not too fast.
Best regards,
Andreas
thank you for your reply. We have underfloor heating almost throughout the basement, so the screed in one of the two windowless basement rooms is now being heated. The second windowless basement room is the utility room, which has no heating.
In both rooms, there are dehumidifiers running, and the humidity level hovers around 65-75% at about 22°C (72°F). The dehumidifiers do not run continuously (their tanks fill up after about 5-6 hours), so I think the drying process is not too fast.
Best regards,
Andreas
Hello "andimann".
The forced drying currently being carried out is the only proper approach given the described building conditions. The fact that the relative indoor humidity has stabilized at 65-70% shows two things:
Firstly, that the drying measure is working (otherwise the value would be even higher), and secondly, that this measure is necessary (otherwise the value would settle lower than currently measured).
All in all, this approach is the right one!
Regards, KlaRa
The forced drying currently being carried out is the only proper approach given the described building conditions. The fact that the relative indoor humidity has stabilized at 65-70% shows two things:
Firstly, that the drying measure is working (otherwise the value would be even higher), and secondly, that this measure is necessary (otherwise the value would settle lower than currently measured).
All in all, this approach is the right one!
Regards, KlaRa
Hello KlaRa,
Current status:
We currently have a large construction dehumidifier (Trotec 170 Eco) running in the 45 m² (480 sq ft) basement room and a household appliance (Comfee something) operating in the utility room.
Two more Trotec TTK 105 units are on their way.
The large construction dehumidifier seems to be very effective; last night the humidity in the basement dropped below 50%, although the temperature was also 27°C (81°F). The heating is now running with a flow temperature of 38°C (100°F). The dehumidifier is currently extracting a bit more than one liter (about 34 fluid ounces) of water per hour from the air, and the 6-liter (about 1.6 gallons) tank fills up every 5 hours.
Interestingly, the small household dehumidifier only manages about one-fifth of the water volume compared to the large one, even though it consumes about half the electricity. The efficiency seems rather moderate…
Now I’m curious whether we’ll be able to dry the screed in time. We want to start with the parquet flooring on October 31. That gives us a good 4 weeks to go…
Best regards,
Andreas
Current status:
We currently have a large construction dehumidifier (Trotec 170 Eco) running in the 45 m² (480 sq ft) basement room and a household appliance (Comfee something) operating in the utility room.
Two more Trotec TTK 105 units are on their way.
The large construction dehumidifier seems to be very effective; last night the humidity in the basement dropped below 50%, although the temperature was also 27°C (81°F). The heating is now running with a flow temperature of 38°C (100°F). The dehumidifier is currently extracting a bit more than one liter (about 34 fluid ounces) of water per hour from the air, and the 6-liter (about 1.6 gallons) tank fills up every 5 hours.
Interestingly, the small household dehumidifier only manages about one-fifth of the water volume compared to the large one, even though it consumes about half the electricity. The efficiency seems rather moderate…
Now I’m curious whether we’ll be able to dry the screed in time. We want to start with the parquet flooring on October 31. That gives us a good 4 weeks to go…
Best regards,
Andreas
Note on the further use of a drying device:
Be careful not to dry too quickly!!
Drying (especially of screed) requires time.
If you dry too fast by using several condensation dryers, the capillaries in the upper screed edge zones will break after initial progress. They dry out.
At that point, even though there is still enough moisture in the screed structure for capillary moisture release, the further drying can only take place through diffusion.
No matter how hard the drying devices work then, the additional drying results will be limited.
This means:
The confident homeowner looks at the collecting container of the dryer, is pleased with the low yield, and wrongly assumes that the drying process is now complete. Until the floor layer installer (in this case, the parquet installer) brings them back to reality with the unexpectedly high result of their CM residual moisture measurement.
This shows that “more is better” can be true in many everyday situations.
However, from a drying perspective and especially regarding cement screed, this can be completely wrong!
--------------------
KlaRa
Be careful not to dry too quickly!!
Drying (especially of screed) requires time.
If you dry too fast by using several condensation dryers, the capillaries in the upper screed edge zones will break after initial progress. They dry out.
At that point, even though there is still enough moisture in the screed structure for capillary moisture release, the further drying can only take place through diffusion.
No matter how hard the drying devices work then, the additional drying results will be limited.
This means:
The confident homeowner looks at the collecting container of the dryer, is pleased with the low yield, and wrongly assumes that the drying process is now complete. Until the floor layer installer (in this case, the parquet installer) brings them back to reality with the unexpectedly high result of their CM residual moisture measurement.
This shows that “more is better” can be true in many everyday situations.
However, from a drying perspective and especially regarding cement screed, this can be completely wrong!
--------------------
KlaRa
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