Moisture meters for concrete, screed and construction are specialised instruments for measuring the moisture content of building materials: structural concrete, cement and anhydrite screeds, plaster, bricks, blocks and construction materials. Checking moisture before laying a floor covering (parquet, porcelain stoneware, resins, paints) is essential to avoid delamination, lifting and trapped moisture that compromises the durability of the covering. The technologies used are varied and complementary: capacitive and resistive electronic meters, F2170 RH probes (the equilibrium method) and thermogravimetric balances (the CM or gravimetric method).
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Electronic moisture meters for construction
Capacitive electronic meters for construction use plate or ball sensors placed on the concrete surface: the electric field penetrates up to 30-50 mm and measures a change in dielectric constant proportional to the moisture. They are quick and non-destructive, ideal for scanning large areas and identifying locally wetter zones. They give values on a dimensionless scale (0-100, 0-200 depending on the model) or convert to moisture % by mass using calibration curves specific to the material. They are indicative: for formal quantitative measurements, standardised methods such as F2170 or CM are used.
F2170 RH probes
The in-situ RH (Relative Humidity) probe method, governed by ASTM F2170, is the international reference for accurately measuring concrete moisture before laying floor coverings. A hole is drilled in the concrete (to a depth of 40% of the slab thickness), a protective sleeve is inserted, and a capacitive humidity probe is placed inside. After 24-72 hours of stabilisation, the probe measures the relative humidity of the air inside the hole, in equilibrium with the surrounding concrete. The RH value obtained is compared with the covering manufacturer’s limits (typically ≤ 75-80% RH for parquet; ≤ 90% RH for epoxy resins).
CM (carbide) method
The CM (Calcium Carbide Method) is the traditional reference method in Europe for measuring the moisture of cement and anhydrite screeds. A sample of screed is taken and mixed with calcium carbide powder (CaC2) in a sealed metal bottle fitted with a pressure gauge: the water in the screed reacts with the CaC2 to produce acetylene gas (C2H2), whose measured pressure corresponds to the quantity of water in the sample. Modern CM kits are compact and portable, with conversion tables for calculating the moisture % by mass. The typical specifications for laying parquet are ≤ 2% for cement and ≤ 0.5% for anhydrite (expressed as total moisture, not to be confused with the F2170 figures, which are expressed as equilibrium RH).
Thermogravimetric balances
Laboratory thermogravimetric balances determine moisture by drying: the concrete or screed sample is weighed before and after oven drying at 105 °C to constant weight. The percentage difference gives the moisture by mass with excellent accuracy. The method is destructive and slow (24-48 hours) but is the reference for absolute precision. In construction it is used to validate electronic instruments and for formal analysis in the event of a dispute.
Applications
The applications include: quality control before laying parquet, porcelain stoneware, resins and floor paints (every covering requires properly dried screeds); checking structural concrete for durability and mechanical performance; inspection of rising damp in walls; monitoring the curing of concrete pours on site; checking moisture in plaster mortars before painting; and expert assessments and disputes over moisture problems in buildings.
Reference standards
The main standards are: ASTM F2170 (in-situ RH probe, the US reference); UNI 10329 (calcium carbide CM method); ASTM D4263 (plastic sheet test for surface moisture); UNI EN 13892 (screeds, test measurements); BS 8203 (UK, substrate preparation for floor coverings); EN 14157 (concrete); ASTM E1907 (USA). The acceptance specifications are set by the manufacturers of the coverings and must be verified before laying.
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The Tramex impedance moisture meters distributed by RODER for this quantity: technical data sheets on roder.it, availability and quotations on innovacheck.com.
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