Cement screed with underfloor heating does not dry further?!

Hello,

I am a female builder from S-H and absolutely desperate. Apart from the fact that I hardly know anything about screed, I would like to turn to you with my problem:

We have been building a small single-family house (135 sqm, solid) since summer. On 17.10.17 our cement screed (6 cm thick) was laid. We have underfloor heating throughout the house. After 2 days we were allowed to walk on the screed and after one week we started ventilating (every morning and every evening 10 minutes of shock ventilation).

Since 15.11.17 the drying program of the underfloor heating has been running and we have always wiped the moisture on the windows, concrete ceiling, and doors with towels during ventilation.

Since 16.11.17 a large construction dryer has been running. And since 23.11. a second smaller construction dryer (one downstairs, one upstairs).

On 04.12.17 a residual moisture of 2.8% was measured in the screed (unfortunately only at one spot). It was a CM measurement. After that we started painting and plastering the walls (probably bringing moisture back in?).

On 11.12.17 another measurement was taken, same measurement technique: in several rooms and upstairs and downstairs: different values between 2.7% and 3%.

We are so desperate! We have to move out of our apartment at the end of December and have already had to postpone our kitchen installation and staircase installation to early January. That means we will probably move in on 31.12.17 without stairs and kitchen and flooring.

Carpet (with adhesive/fixation) is to be laid upstairs and vinyl (with leveling compound / adhesive) downstairs, we will do it ourselves.

But we will never reach 1.8%!!!!? Many say it should have been dry long ago... The screed installer told us that this is strange and we should sometime soon close everything for 3 days, run the construction dryer and heating and not enter the house.

Has the screed suffered the so-called "capillary break"? We are so scared of that!

What did you do, how did you dry, and what were the moisture measurements like?

I am thankful for any smallest help or advice!

Kind regards,

Cara

Dehumidifiers only help if there is one in every room. Spackling and painting are absolutely not possible during this time.

Hello,
so for me it took about 6 weeks until the screed had 2%. And the only thing that helps is ventilating, ventilating, ventilating. The normal construction dryers simply do not remove enough moisture from the house. I placed humidity meters in every room and whenever I had over 60% humidity, I opened the windows. After ventilating, I briefly had 40%. You can really see how everything dries out.

You can only get the water out when the air is nice and dry. And at the moment, conditions are optimal because it is nicely cold outside.

But not in SH. I can’t remember such a wet autumn. Rain rain rain. Honestly, it’s not easy to get the screed dry now. Which doesn’t help you either....

See it like Nordlys. It’s probably due to the weather. The longer duration just clashes with your way too tight schedule.

There’s really no helping you there. Just reassure you that it will get better.

Is there a possibility to take a temporary room and store the furniture for a month?

Moving in and then partially moving out again for follow-up work is very inconvenient.

Hello,

as long as it is <= 5 degrees outside and 20 degrees inside, rain is no problem. That is why it is called relative humidity. If I take 5-degree cold air and assume it has 100%, then the same air at 20 degrees only has 40% relative humidity. This is because air can hold more water the warmer it is.

5-degree warm air binds a maximum of 6.9g/m³ water = 100%, 20-degree warm air can hold 17.3 g/m³ = 100%. So if I bring cold air into the house (even if it is raining, more than 100% is not possible), I dry out the house.

A small calculation: a 25sqm room has a volume of 62m³. At 20 degrees and 100% humidity, that is about 1 liter of water. Now I completely exchange the air once with 5-degree cold air (100%). Then I still have 0.43l water in the air. Now I earth-heat this air to 20 degrees. Then it can take up another half liter and takes it from the surroundings, such as walls, floor, etc.

That is why it is important to ventilate even when it is raining, as long as the outside air is colder than inside. In summer, it would be much worse because the effect is reversed.

Many people do this wrong. I have this discussion every year again with my tenants. They think they have to ventilate the basement in summer and wonder why it becomes damp.

Even better, of course, is if there is frost, i.e., under 0 degrees, then the effect is even greater.

This is how a building dryer works. It is basically an inverted refrigerator. It has a 'cooling plate' over which warm air is blown. By cooling the air, the storage capacity of the air for water is reduced, the water condenses on the plate and drips into a cup. Then the air is reheated, takes up moisture again, etc....

The cold air from outside has the advantage that I get it for free and do not have to cool it down first using a building dryer.

Therefore ventilate, ventilate, ventilate....