ᐅ Leave the concrete slab exposed over the winter months

nasenmann schrieb:

Even with a prefabricated house, the interior finishing takes time (screed drying, etc.)

There are also options like dry screed, etc.

The winter does not affect the foundation slab as long as the concrete has had enough thaw-free time to reach its initial strength (21 days). So it is better to pour concrete in October rather than January. (Although with additives, work in freezing conditions is also possible.)

Drying out a building in winter is not related to the lower air humidity, but is a special property of water. It changes directly from solid to gas, drying out the building (sublimation). The story about cold air drying better is based on a different physical principle: relative humidity. The warmer the air, the more water vapor it can hold. When cold air is brought inside a building and warmed by the ground temperature, it can hold more moisture. That’s why a closed, heated building dries faster in winter than in summer. You can easily test this by placing a hygrometer in an airtight box inside a freezer. The humidity will steadily rise... then remove the box and the humidity will decrease again.

By the way, this is a well-known problem for mold forming on thermal bridges. The wall surface is colder, warm air passes by, cools down, and reduces its ability to hold moisture—leading to condensation on the wall and mold growth.

Thank you for your responses

Tom1607 schrieb:
The winter does not affect the foundation slab as long as the concrete has had enough frost-free time to reach its initial strength (21 days). So it’s better to pour concrete in October rather than January. (Although with additives, work can also be done in freezing conditions).

By the way, drying during winter has nothing to do with lower humidity but is a special property of water: it changes directly from solid to gas, drying the building in the process (sublimation). The idea that cold air is better at drying relates to a different physical principle—the relative humidity. The warmer the air, the more moisture it can hold. If cold air is brought into a building and heated, it can hold more moisture, which is why a closed, heated building dries faster in winter than in summer. This can be easily tested. Put a hygrometer in an airtight box and place it in a freezer. The humidity will steadily rise… then take it out again, and the humidity will drop.

By the way, this is a well-known cause of mold at thermal bridges. The wall surface is colder, warm air passes by and cools down, reducing its capacity to hold moisture → condensation forms on the wall and mold grows.

Initial strength achieved after 21 days? I have never heard of 21 days for initial strength.

Maybe the original poster and you should check out betontechnische-minus-daten.de to avoid spreading such half-truths.

Phantom schrieb:
Our goal/plan is to move in by March or at the latest April.

Do you have that in writing? That’s going to be very tight, if not impossible: the interior finishing takes just as long as with solid construction.
Or will everything (including the screed) be dried on site?

@costa : thanks for the hint. Quote: "For assessing concrete strength and frost resistance, the 28-day compressive strength is generally decisive."