We have a concrete slab of 10 cm that was cast in December, indoors. The slab has about 20 cm ground insulation underneath, and between the slab and the foundation wall, there is a strip that looks like thick paper.
To the point:
Part of the slab is in the laundry room, and therefore it needs to have waterproofing. Three days ago, the builder measured that it was dry enough for waterproofing. At the time, an electric heater was in the space, keeping it at around 20 degrees in the air. The floor was colder near the walls and corners.
Now, three days later, the builder measures that it is more humid. The heater is no longer in the space (used in a new bathroom being tiled). It is now colder in the laundry room space, down to about +10 in some corners.
The builder doesn't quite understand why.
Question:
Is this solely related to the temperature? I mean, does concrete behave like air, which has higher relative humidity (RH) if it is cooled without simultaneously being dried/dehumidified?
What should he do? Use a dehumidifier to dry out the concrete more? Keep it warm for a while for further drying before the waterproofing is applied?
To the point:
Part of the slab is in the laundry room, and therefore it needs to have waterproofing. Three days ago, the builder measured that it was dry enough for waterproofing. At the time, an electric heater was in the space, keeping it at around 20 degrees in the air. The floor was colder near the walls and corners.
Now, three days later, the builder measures that it is more humid. The heater is no longer in the space (used in a new bathroom being tiled). It is now colder in the laundry room space, down to about +10 in some corners.
The builder doesn't quite understand why.
Question:
Is this solely related to the temperature? I mean, does concrete behave like air, which has higher relative humidity (RH) if it is cooled without simultaneously being dried/dehumidified?
What should he do? Use a dehumidifier to dry out the concrete more? Keep it warm for a while for further drying before the waterproofing is applied?
I don't have knowledge about newly poured slabs. However, I recently had a water leak in a basement shower area. The slab was obviously damp. We tore everything down and after drying out with a dehumidifier and heat plates, the "drying guy" drilled two holes in the slab to measure the moisture content. Since that apparently wasn't sufficient, we had to dry for a while longer and drill new holes. The holes were about 2cm deep.
The message here is that you can't measure on the surface. How did your craftsman do it?
The message here is that you can't measure on the surface. How did your craftsman do it?
Yes, I have read something about the correct way being to measure in drilled holes and that is surely correct.PASwe said:
The builder uses a moisture indicator (I think that's what it's called), something like this: http://www.mycoteam.no/bilder/1665/1743?size=extramedium
Apparently, such a device does not necessarily provide a correct absolute value, but if I understand it correctly, it can be used to detect differences. In my case, there are two corners that are now giving too high a reading, even though they were OK on the instrument earlier.
Yes, that's the case.Prosit said:
Relative humidity is the ratio between the current amount of moisture and the maximum amount of moisture that the air can carry at that specific temperature.
I want to argue that the builder is measuring incorrectly. Or at least using a method unsuitable for the purpose.
When the rH in the newly cast slab drops below 100%, the rH will be the same as the rH in the air in the concrete pores.
If there is free water in the pores, the rH is 100%, and when the rH drops below 100%, the water will be in vapor phase in the concrete pores.
I think the builder is measuring a bit foolishly.
If you heat and dry a newly cast concrete slab very hard - a lot of heat, air exchange over the surface, and together with a dehumidifier, you can probably get the surface dry enough in just a day, while a cm down in the concrete the rH might still be 100%.
The diffusion rate is slow in concrete, and the moisture content through the cross-section often holds some kind of exponential value with one-sided drying.
That the rH rises when you remove the heat supply may indicate that there is significantly more moisture a bit below the surface.
But the temperature change itself is also a major culprit in the drama.
What rH did you measure at 20° vs 10°?
There's a lot to read here:
http://www.rbk.nu/Fuktmatningsmanual.asp
When the rH in the newly cast slab drops below 100%, the rH will be the same as the rH in the air in the concrete pores.
If there is free water in the pores, the rH is 100%, and when the rH drops below 100%, the water will be in vapor phase in the concrete pores.
I think the builder is measuring a bit foolishly.
If you heat and dry a newly cast concrete slab very hard - a lot of heat, air exchange over the surface, and together with a dehumidifier, you can probably get the surface dry enough in just a day, while a cm down in the concrete the rH might still be 100%.
The diffusion rate is slow in concrete, and the moisture content through the cross-section often holds some kind of exponential value with one-sided drying.
That the rH rises when you remove the heat supply may indicate that there is significantly more moisture a bit below the surface.
But the temperature change itself is also a major culprit in the drama.
What rH did you measure at 20° vs 10°?
There's a lot to read here:
http://www.rbk.nu/Fuktmatningsmanual.asp
RH has probably not been measured "for real" as it has only been measured with an indicator on the surface. At least he hasn't mentioned any value, he just checks if the gauge needle is in the correct or incorrect area.
The slab was cast almost exactly 2 months ago, and self-leveled a couple of weeks ago. It wasn't very warm before the self-leveling and the first few days after the leveling.
There are only two areas that are not dry according to the instrument now, but they were apparently dry last week - although the dehumidifier had been running there for a few days.
Now there will be no full surface waterproofing in the laundry room, just around the edges and slopes around the floor drains. I note that it is OK during renovation according to BKR, as the house does not have insulated foundation walls.
The slab was cast almost exactly 2 months ago, and self-leveled a couple of weeks ago. It wasn't very warm before the self-leveling and the first few days after the leveling.
There are only two areas that are not dry according to the instrument now, but they were apparently dry last week - although the dehumidifier had been running there for a few days.
Now there will be no full surface waterproofing in the laundry room, just around the edges and slopes around the floor drains. I note that it is OK during renovation according to BKR, as the house does not have insulated foundation walls.