Having acquired a floor hygrometer (foam box with temp / humdity sensor in it & butyl tape) i've started checking the humidity of a ~ 50 year old ground floor slab. Construction i think is 50mm screed above DPC. not sure what's below the DPC, but i guess another 100mm of concrete.
I have only done one measurement so far, in a hall cupboard - reset sensor; sealed box to slab left for 24 hrs then measured for 6hr - and got a relative humidity of 76% Rh @ 18.5C.
This seems quite high to me. I need to do more measurements in the same and other locations, and intend to do a spot calibration check (https://www.vernier.com/til/4337) with water and table salt (NaCl) to confirm the sensor is reading right.
What sort of surface humidity values should i be expecting ?
I have only done one measurement so far, in a hall cupboard - reset sensor; sealed box to slab left for 24 hrs then measured for 6hr - and got a relative humidity of 76% Rh @ 18.5C.
This seems quite high to me. I need to do more measurements in the same and other locations, and intend to do a spot calibration check (https://www.vernier.com/til/4337) with water and table salt (NaCl) to confirm the sensor is reading right.
What sort of surface humidity values should i be expecting ?