ᐅ Cement screed without chemical additives does not properly dry.
Created on: 25 Nov 2025 13:00
B
BrnZck91
Hello everyone!
On September 3rd, we had 65mm (2.6 inches) of cement screed installed (without chemical additives).
The heating protocol was followed, and we ventilated the house three times daily for 10-20 minutes each time. Several calcium carbide (CM) measurements have already been taken, and even after following the heating schedule, we consistently maintained heating up to 30°C (86°F).
During this time, plasterers and painters were also present. However, that was almost three weeks ago now.
Tomorrow the screed will have been laid for 12 weeks, and the last CM measurement taken last Monday still showed 2.6%.
On the recommendation of the screed company, we have since increased the heating to 45-50°C (113-122°F) up to today and also set up a construction dryer and a smaller room dehumidifier. Someone from the screed company visited today and couldn’t explain the situation. Inside the house, there is no noticeable moisture. It does not smell damp. There is no condensation on the windows, and the humidity levels on three hygrometers placed throughout the house range between 35-44%.
Still, the electronic moisture meter shows values between 1.7 and 2.2, and when the meter is placed in the hole left by earlier CM measurements, it even rises up to 2.7. I am at a loss.
The screed installer contacted another floor installer who recommended lowering the heating to 25°C (77°F), so that the air temperature stabilizes around 20°C (68°F). The reasoning was that the devices do not work correctly at higher temperatures (currently the air temperature is over 35°C (95°F)). The electronic moisture meter even showed 3.0% on the concrete stairs, which seems unlikely. But the CM measurements were done by the tiler and flooring installer, often together using two different devices alternately.
We only have one more measuring point left, and the furniture is arriving on December 9th.
The flooring installer also suggested applying an epoxy resin coating to prevent moisture from rising. To allow space for any ascending moisture, he plans to leave out the baseboards for now. This is not possible in the bathrooms, of course, since there will be tiles on the floor and walls.
I really hope someone here can help. I am getting desperate.
On September 3rd, we had 65mm (2.6 inches) of cement screed installed (without chemical additives).
The heating protocol was followed, and we ventilated the house three times daily for 10-20 minutes each time. Several calcium carbide (CM) measurements have already been taken, and even after following the heating schedule, we consistently maintained heating up to 30°C (86°F).
During this time, plasterers and painters were also present. However, that was almost three weeks ago now.
Tomorrow the screed will have been laid for 12 weeks, and the last CM measurement taken last Monday still showed 2.6%.
On the recommendation of the screed company, we have since increased the heating to 45-50°C (113-122°F) up to today and also set up a construction dryer and a smaller room dehumidifier. Someone from the screed company visited today and couldn’t explain the situation. Inside the house, there is no noticeable moisture. It does not smell damp. There is no condensation on the windows, and the humidity levels on three hygrometers placed throughout the house range between 35-44%.
Still, the electronic moisture meter shows values between 1.7 and 2.2, and when the meter is placed in the hole left by earlier CM measurements, it even rises up to 2.7. I am at a loss.
The screed installer contacted another floor installer who recommended lowering the heating to 25°C (77°F), so that the air temperature stabilizes around 20°C (68°F). The reasoning was that the devices do not work correctly at higher temperatures (currently the air temperature is over 35°C (95°F)). The electronic moisture meter even showed 3.0% on the concrete stairs, which seems unlikely. But the CM measurements were done by the tiler and flooring installer, often together using two different devices alternately.
We only have one more measuring point left, and the furniture is arriving on December 9th.
The flooring installer also suggested applying an epoxy resin coating to prevent moisture from rising. To allow space for any ascending moisture, he plans to leave out the baseboards for now. This is not possible in the bathrooms, of course, since there will be tiles on the floor and walls.
I really hope someone here can help. I am getting desperate.
Okay. What is your final recommendation for me? Is the described approach—heating up until next Wednesday plus using a construction dryer and dehumidifier—the right one?
Honestly, I have no desire or energy for trouble or a legal dispute with the screed company in the current situation... I also think that the phrase "on average" allows for some flexibility...
Honestly, I have no desire or energy for trouble or a legal dispute with the screed company in the current situation... I also think that the phrase "on average" allows for some flexibility...
First, do the vapor barrier test properly. Set the flow temperature for the underfloor heating to a normal level, approximately 26-28°C (79-82°F). Open the window where the vapor barrier is located.
Did you mention that the screed was ground down? I couldn’t find that information when checking back, but I remember it. If not, it should be done. It’s possible that a weak layer of laitance has formed. Otherwise, continue with the surface readiness heating (flow temperature) and use a dehumidifier. After 14 weeks, I would simply proceed with the floor covering. However, it might be better to leave out the skirting boards initially and install them later yourself (in case the vapor barrier test still shows moisture slightly above 70% but below 80%). If there is too much moisture beneath the vapor barrier, unfortunately wait and repeat the test after another week.
Did you mention that the screed was ground down? I couldn’t find that information when checking back, but I remember it. If not, it should be done. It’s possible that a weak layer of laitance has formed. Otherwise, continue with the surface readiness heating (flow temperature) and use a dehumidifier. After 14 weeks, I would simply proceed with the floor covering. However, it might be better to leave out the skirting boards initially and install them later yourself (in case the vapor barrier test still shows moisture slightly above 70% but below 80%). If there is too much moisture beneath the vapor barrier, unfortunately wait and repeat the test after another week.
Tolentino schrieb:
Did you mention that the screed was ground? I couldn’t find it when I scrolled back but I remembered it.
If not, it should be done again. It’s possible that a sinter layer has formed. Sorry, Tolentino, you seem to be confusing something here.
This concerns a cement screed, not a calcium sulfate screed.
The so-called “sinter layers” used to be notorious with calcium sulfate self-leveling screeds (and only with those), as additives would settle on the surface as hard shells during curing.
However, with cement screeds, such negative phenomena do not occur and have never occurred!
Tolentino schrieb:
First, do the vapor barrier test correctly. Use the normal flow temperature for the underfloor heating, estimated around 26-28°C (79-82°F). Open the window in the room where the vapor barrier is placed. What does "AT" mean? The plumber set it to 50 degrees again around 3 p.m. I will be on site again around 10 p.m. today. Should I put the vapor barrier back on and leave the window in that room slightly open overnight for about 12 hours while keeping all other windows closed, or can I just leave yesterday’s vapor barrier in place until tomorrow?
Tolentino schrieb:
Did you say the screed was ground down? I couldn’t find it by scrolling back but I remember it.
If not, do that again. It’s possible that a sintering layer has formed. The screed was completely ground down yesterday. I actually thought the floor installer had done this last week, but at least he did it yesterday.
Tolentino schrieb:
Otherwise, continue heating up the floor for readiness (flow temperature) and use dehumidifiers. After about 14 weeks, I would just install the flooring. But maybe leave out the baseboards for now and install them later yourself (if the vapor barrier test still shows moisture slightly above 70% but below 80%). If the floor installer pours the leveling compound next Sunday, that will be almost 14 weeks. Leaving out the baseboards is an option.
One more question about using the construction dryer: I have set it to remove any moisture from the air (including moisture below 30%). Is this a reasonable setting, or would a higher level be more appropriate?
I want to do everything right over the next few days because we are running out of time, and of course, I want to avoid any moisture problems in the future...
I want to do everything right over the next few days because we are running out of time, and of course, I want to avoid any moisture problems in the future...
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