Vaisala SHM40 - Manual (Page 18)

USER'S GUIDE____________________________________________________________________
16 __________________________________________________________________ M211423EN-B
Measurement Depth
The borehole must reach deep enough into the concrete structure to
provide a representative humidity condition. The correct depth of the
borehole is affected by the drying conditions of the concrete structure:
- When drying occurs from one side only, the measurement depth (d) is
40 % of the depth of a slab. See Figure 2 on page 17.
- For a concrete slab that is exposed to air on both sides, the minimum
depth of measurement (d) is 20 % of the depth of the slab. See Figure
3 on page 17.
The minimum measurement depth using standard SHM40 accessories is
30 mm, maximum is 90 mm.
Humidity Profile
The humidity profile of the slab depends on the drying conditions of the
concrete: whether the concrete dries in one or in two directions. In
concrete slabs that dry in two directions, the humidity is highest in the
middle. If a floor coating is applied, the humidity spreads evenly
throughout the slab until it corresponds to readings measured at the depth
of approximately 20% of the slab.
In concrete slabs that dry in one direction only, the humidity is highest at
the bottom. If a floor coating is applied, the humidity spreads evenly
throughout the slab until it corresponds to readings measured at the depth
of approximately 40% of the slab.