ᐅ The screed will not be fully dry after 10 weeks, even with a heating schedule.

Hello,

On July 12th, we had 7 cm (3 inches) of cement screed installed throughout the entire house.
Since there was no rush, we only started the heating program on September 24th. So the screed had actually been drying for about 11 weeks.

The majority of the water should be out by now; the floor coverings are next, which is why the hot air blower was turned on.

We heated according to the "program" provided by my heating technician, in coordination with the screed installer, until October 11th. I understand this is not the usual "standard program," which I personally think is preferable, since no new build needs a 55-degree Celsius (131°F) supply temperature nowadays. The screed will never see that with our heat pump. The maximum supply temperature according to calculations is 35 degrees Celsius (95°F).

Our heating schedule was as follows:

1: 30°C (86°F)
2: 35°C (95°F)
3-5: 45°C (113°F) (so the screed experienced a higher temperature)
6-12: 35°C (95°F)
13-17: 40°C (104°F) (after the first quick test, it was still too damp, so the supply temperature was raised again)
18: 35°C (95°F)
19: 30°C (86°F)

But hopefully, that’s not the main issue. I am still puzzled that after such a long time, my tiler still finds a CM (calcium carbide) moisture test unnecessary because his moisture meter (from GANN) still shows 65 digits. I understand the intention behind preliminary testing, but I don’t understand why everything still seems so damp?

Yes, I ventilate 3-4 times daily with cross-ventilation. I have two hygrometers in the house, and I ventilate as long as the humidity inside decreases, which is usually around 10 minutes. I do not want to connect multiple industrial dehumidifiers to the hot air blower because that would drive the cost through the roof.

My questions:
Should I keep the windows tilted open in principle? Even at night? Or keep them tilted open plus ventilate quickly during the day and close them at night? Or only ventilate quickly?
Should I avoid ventilation altogether in rainy weather? Warm and saturated air with moisture should be removed anyway, right?
Is there a minimum supply temperature that should be maintained?

Apart from the “special program,” what else could be causing this?

Thank you all.

joschua_85 schrieb:

Apart from the "special program," what else could be the reason?

Only the special program. This is roughly what the normal program looks like (3–4 weeks after screed installation).
At that point, you are far from those temperatures, but especially also from the required time. No heat pump installed yet that you could simply run at 35°C (95°F)? Just wait another 1–2 weeks.

It’s a brine pump, and the heating engineer keeps telling me the same story about frozen collectors, the ground being “dead” during winter, and so on. He only wants/would run it with the Hotboy. Not to mention that he hardly finds the time to adjust it...

Does the “dwell time” already count when you extract the heating program, or why does it start on day 21?
As I said, I won’t be running 55°C (131°F) into the screed either! So, I guess waiting is the only option?

joschua_85 schrieb:

No, it's a brine pump.

Then it’s better not to heat up via the heat pump – but 30 degrees Celsius (86°F) should be achievable, like in winter.

joschua_85 schrieb:

Does the "lying time" already count when your heating program ends, or is that why it starts on day 21?

Yep – wait at least three weeks. So day 21 is the starting point.

Thank you. But as I said, it won’t be installed anytime soon anyway, so the hot water circulator stays.

I just read in another thread about what’s going on with the hot water circulator here. Today alone, I used about 100 kWh in 24 hours with a supply temperature of 30°C (86°F). Does it make sense to reduce the output from 21 kW at a supply temperature of 30-35°C (86-95°F)? Or is it actually helpful for faster and more efficient heating?

Hello "joschua_85"

For heated screeds, the regulations require functional heating followed by the readiness-for-cover heating.
Basically, the purpose of readiness-for-cover heating is to remove the excess mixing water from the screed mortar so that after installing any type of floor covering (textile, elastic, or wood), no damage occurs.
The responsibility to verify the readiness for covering lies solely with the floor installer.
With 65 digits according to GANN, practical experience shows that a CM (calcium carbide) moisture test should definitely be carried out. This digital value is by no means in a range where it would be unreasonable to perform a CM measurement.
At this point, carrying out forced drying seems excessive and unnecessary given the 65 digits reading.
Have a CM measurement done, even if the second test involves additional costs (only the first measurement is generally included in the quoted price).

Whether to keep windows tilted open for continuous ventilation or not—no one can give you a clear answer.
This is because the nights are getting cold at the moment, the outdoor air cools down, and the relative humidity outside inevitably increases.
Allowing damp outside air to enter through tilted windows would not lead to successful (drying) results.
Well, cement screed only noticeably absorbs moisture at around 65-70% relative humidity.
But the conditions are not really favorable for drying the screed, although they will not cause any harm.

Please do the following:
If you don’t already have one, buy a hygrometer.
Place the hygrometer in a representative room, centrally located, close all windows, and check the reading after about 5-8 hours to see if and how it changes.
For example, if you read a relative humidity of around 65%, the floor installer with his 65 digits reading would already have a solid basis.
The screed is definitely ready for a CM test. Without a doubt.

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Best of luck with your project: KlaRa