Can painting work begin during screed drying?

Our screed has now been in the house for almost 4 weeks and of course we have been ventilating properly all the time. Starting soon, hopefully at the beginning of September, we will begin the functional and maturity heating, which will release quite a bit of moisture again.

According to our site manager, we can already start with the filling and sanding work so that afterwards only wallpaper and paint need to be applied. Do you agree with that or should we at least wait 3-4 weeks of heating? We are a bit worried that the plaster might come off the ceiling when heating if we already fill everything now. The kitchen installer is coming on [2nd November]. Until then, painting and flooring work must be finished. Afterwards, we can move in. Therefore, we would like to use the drying time productively so that it doesn't become too stressful at the last minute.

After four weeks, the (I assume cement screed) is already dry enough that you can safely carry out all other work. No more large amounts of moisture will come out. It is said that under normal conditions and average thickness, a cement screed is often dry enough for floor covering after two months.

Just lay a 1x1m piece of plastic sheet on the floor, tape the edges, and check after one day how dry or wet the underside of the sheet is. This is a rough test for readiness for covering - but it helps you get a feel for the moisture in the screed.

After four weeks, the (I assume cement screed) is already dry enough that you can safely carry out all other work. No large amounts of moisture will come out anymore. It is said that under normal conditions and average thickness, a cement screed is often dry enough for floor covering after two months.

Just place a 1x1m sheet of foil on the floor, tape the edges, and check after one day how dry or damp the foil is from underneath. This is a rough test for readiness for covering - but it helps you get a feel for the moisture in the screed now.

Yes, cement screed. Until now, I thought that most of the moisture is only released during heating. Otherwise, why heat it for so long? Currently, the humidity after 24 hours with closed windows is around 80-90%, depending on the floor. By ventilating, we reach about 60%, which on most days corresponds to the humidity shown by the weather app. And yes, the temperature inside and outside is currently almost the same, with a ±1° difference. So we can't ventilate more than that.

What else would you heat for such a long time?

For two reasons.
1. At the beginning, a functional heating is performed. This is to check, according to DIN schlagmichtot, the correct function of the heating with screed (longitudinal expansion, etc.) to ensure during normal operation that nothing has gone wrong. It is also a proof for the heating installer that everything is okay and that he has delivered a proper trade. From the past, when there were no heat pumps with 30-degree supply temperature, most heating-up protocols specified 50-55 degrees supply temperature, as this corresponds to the maximum temperature in underfloor heating. Today, however, often only heating up to 35 degrees or to the maximum design temperature of the heating system is done, which also makes sense if higher temperatures are not operated. You have to see what is required in your case.
The process takes a few days.
2. After that, there is the readiness heating to drive out the last residual moisture from the almost dry screed. This is especially relevant for bonded floors like parquet, as the parquet adhesive acts almost like a moisture barrier. Tiles are less sensitive in this regard.

For explanation from the web:


The problem is that the screed seems dry after four weeks. But you don’t know whether everything is really okay or not. And even very low moisture levels can still cause significant damage. Therefore, as a craftsman, you always play it safe, whether necessary or not.

In my own properties with heat pumps, I have so far only heated up to supply temperature and then initially checked the moisture myself as described in #2. Then, for safety, I let it run for another two days and that’s it – but you can only do this at your own risk and if undertaking the work yourself.

Or you simply sacrifice a few euros at the beginning for a fast-drying screed. With this, parquet installation is possible after just one week – all other work anyway. With good coordination or again doing it yourself, this can be well-invested money if you can move into the house maybe two months earlier.

For two reasons. 1. At the beginning, functional heating is done. This way, according to DIN schlagmichtot, the correct function of the heating with screed (longitudinal expansion etc.) is tested, so that in normal operation it is ensured that nothing went wrong. It is also proof for the heating installer that everything is okay and that he delivered a proper trade. From the past, when there were no heat pumps with 30-degree flow temperature yet, most heating-up protocols specified 50-55 degrees flow temperature, since this matches the maximum temperature in underfloor heating. Today, however, heating is often done only up to 35 degrees or up to the maximum design temperature of the heating, which also makes sense if no higher temperatures are operated. You have to see what is required for you. The fun lasts a few days. 2. Afterwards, there is the readiness heating to drive out the last residual moisture from the almost dry screed. This is especially relevant for glued floors like parquet, since the parquet adhesive acts almost like a moisture barrier. Tiles are less sensitive in this regard.

Explanation from the internet:

The problem is that after four weeks the screed seems dry. But you do not really know whether everything is fine or not. And even very low moisture can still cause severe damage. Therefore, craftsmen always play it safe, whether necessary or not.

In my own properties with heat pump, I have so far only heated up to flow temperature and then first checked the moisture myself as in #2. Then I let it run for two more days for safety, and that's it – but you can only do this at your own risk and with your own work.

Or you simply sacrifice a few euros at the beginning for a fast-drying screed. This makes parquet installation possible after just one week – all other work anyway. With good coordination or also again your own work, this can be well-invested money if you can move into the house maybe two months earlier.

Thanks for all the information. Let me summarize: The worst of the moisture is probably almost gone, but the residual moisture is removed with the heating. In our case, it should be click vinyl, so we should get down to about CM-2% residual moisture, if I googled correctly. The tiler is also coming to us and he will do a CM measurement anyway, so then we will have an interim report. However, I would still not wallpaper yet, but spackling, etc. should already be possible. I do find it surprising, though, that our house was never really wet inside. We did have 99% humidity, but our neighbors in the development area told us about wet, dripping ceilings, etc. However, they all dried in winter/spring at low temperatures. This year, spring went straight from 10° to 30° in May/June. We had at most wet windows from the inside, but not really much of that.

We did have 99% humidity, but our neighbors in the building area told us about wet, dripping ceilings, etc.

That's obvious. Moisture condenses on cold surfaces. That will be difficult in summer ;-)