Choosing the right time for installing tiles, parquet, or vinyl flooring is crucial. If the substrate is still too damp, issues such as cracking, mould, or loss of adhesion can occur. Especially in new builds, renovations, or screed repairs, professional moisture testing is indispensable to identify the optimal moisture level for further processing.
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CM Meter Classic, Art. No. 40424
The robust classic for everyday job site use. The analogue pressure gauge is especially durable. The set includes all essential components such as ampoules, measuring container, scale, and manual. Ideal for tilers, floor layers, and surveyors.
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Digital CM Meter incl. Printer, Art. No. 40470
The digital system for those who value thorough documentation. With a digital pressure gauge, precise readouts, and direct reporting function. Ideal for handovers, inspections, or construction records.
Advantages of Karl Dahm’s CM measuring devices:
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Easy to use thanks to complete sets
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High measurement accuracy
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Includes carry case, scales, and ampoules
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Optional mobile printers for instant reports
Moisture Meters for Various Building Materials
CM testing is not always required. For quick pre-checks and surface moisture evaluations on walls, screed, or wood, we recommend our electronic moisture meters.
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Moisture Meter GM-200, Art. No. 40435
Versatile use with 9 material settings for screed, concrete, gypsum plaster, and wood. Compact, ergonomic, and ready to use with no recalibration required.
Tip: Electronic moisture meters are ideal for quick pre-checks but do not replace the mandatory CM measurement for screed work.
Step-by-Step Guide to the CM Measurement
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Sample extraction: A representative screed sample is taken from depth using a chisel or milling tool.
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Crushing and weighing: The sample is crushed into small pieces and weighed precisely.
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Reaction: In a sealed measuring vessel, the sample is mixed with a calcium carbide ampoule. The chemical reaction generates acetylene gas.
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Pressure measurement: The gas increases pressure, which is displayed via a gauge (analogue or digital).
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Reading the result: The display shows the percentage moisture content of the sample.
The result is available after approx. 10–20 minutes and provides a reliable basis for decision-making.
The Benefits of the CM Method at a Glance
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Officially recognised method according to DIN EN
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Accurate, reproducible results
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Easy to use on site
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High reliability for inspections and flooring readiness
FAQ – Frequently Asked Questions About CM and Moisture Testing
What exactly is CM measurement?
The calcium carbide method (CM method) is used to determine the residual moisture in mineral-based materials such as screed. Calcium carbide reacts with the water in the sample to produce acetylene gas. The resulting pressure is measured to determine the moisture content. This method is legally recognised in the construction industry and delivers reliable results.
When is a CM test necessary?
A CM test is required whenever the readiness for covering of screed must be reliably confirmed. It is especially important before laying flooring such as tiles, laminate, parquet, or carpet, to prevent future moisture damage.
What is the difference between a CM test and an electronic moisture test?
Electronic moisture meters provide quick, non-destructive readings of surface moisture, ideal for preliminary assessments. The CM test, however, determines the actual core moisture content and is the legally reliable method for confirming flooring readiness.
What is the maximum moisture content allowed in screed?
Permitted values vary by screed type and usage: For unheated cement screed, max. 2.0 CM-%; for heated variants, 1.8 CM-%. Anhydrite screed allows max. 0.5 CM-% (unheated) or 0.3 CM-% (heated). These limits are crucial to prevent damage.
How long does a CM test take?
The measurement takes approx. 10 to 20 minutes, depending on room temperature and sample consistency. Proper sampling and accurate crushing/weighing are essential for reliable results.
Are Karl Dahm measuring devices calibratable?
Yes, all CM meters from Karl Dahm can be regularly checked and calibrated if necessary. This ensures long-term measurement accuracy and compliance with industry standards.
What is included with the CM measuring kits?
Karl Dahm sets are fully equipped: Each kit contains the measuring device (analogue or digital gauge), precision scale, steel balls, calcium carbide ampoules, measuring cylinder, seals, work gloves, manual, and a robust transport case.
How is the result documented?
With the digital CM device (Art. No. 40470), documentation is automatic via the built-in or mobile printer. The result can be printed directly on-site and added to the project record. With the Classic model (Art. No. 40424), results are noted manually.
What should I do if the moisture level is too high?
If residual moisture is too high, the screed must continue drying. Recommended measures include cross-ventilation, dehumidifiers, or controlled heating. Repeat testing should be carried out after sufficient drying time.
Can these devices be used with other materials?
The CM test is designed specifically for screed and similar materials. For walls, concrete, gypsum, or wood, electronic moisture meters like the GM-200 (Art. No. 40435) are more suitable, offering non-destructive and quick results.
How often should moisture testing be done?
In new constructions or with fresh screed, the first test should be conducted after about 4 weeks of drying. Follow-up tests at regular intervals help monitor drying progress and identify the optimal time for installation.
Can I use the CM test for mixed or self-levelling screeds?
Yes, these types can also be tested using the CM method. However, ensure that the sample is homogeneous and representative. With self-levelling screeds, sufficient drying before sampling is essential.
How reliable is the CM test legally?
In Germany, the CM method is recognised as state-of-the-art and meets the requirements of various standards (e.g., DIN 18560). It serves as valid documentation during inspections or handovers and is recommended for legal and liability reasons.
Discover the premium moisture testing and CM measuring devices at the Karl Dahm online shop – precise, reliable, and built for real-world use on site.
