maxit floor Moisture Environment Concepts  
   
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Humidity Measurement
Questions

CM Method

CM-method for moisture measurement of maxit Floor products 
 

Content

Principle
Sampling
Testing
Maximum humidity in maxit floor products
Critical issues
Conversion Table (gas pressure - water content)
 
Principle


The CM tester works according to the carbide method using the well-known destruction of calcium carbide in water. During this reaction acetylene gas is formed, which causes an increase in pressure in the steel cylinder.

From the measured pressure and the test portion of the material to be tested, the water content of the sample is read from a table, or directly from the manometer.

Sampling                                                                                                            To Top
  • A representative sample has to be taken from the product to be tested.
  • This should cover the whole thickness of the floor material (levelling/screed).
  • For parquet the sample is taken from the lower to middle area of the screed.
  • Before filling the steel tube, the material has to be crushed and slightly milled in a mortar. The larger pieces of mineral aggregates should be removed.
Testing                                                                                                                To Top
  1. The material is weighed by using a hand scale and put into the CM pressure cylinder.
    • Measure out 100g for screeds based on calcium sulphate.
    • For other screeds, for example based on cement, magnesia, the weight of the sample depends on the water content.
    • With less water more weight of material is required. For example use 50g of material for 3% water content, and 10g of material for 15% water content.
  2. Place the weighed sample in the CM cylinder without losing any. Next, place steel balls in the cylinder. One ampoule of calcium carbide is slid carefully into the cylinder, which is then closed using the manometer head. The ampoule can be broken by shaking the cylinder vigorously. The sample is completely crushed in the CM cylinder by vigorously moving the sample backwards and forwards, and by making circling movements. Take care that the sample does not touch the manometer. Duration: 2 minutes.
  3. 5 minutes after the CM device has been closed, the sample is shaken as above for another minute.
  4. 10 minutes after the CM device has been closed, the sample is again shaken for approximately 10 seconds. The resulting value is read.
The % water content can be worked out from the conversion chart below.
  • Note: On calcium sulphate based screeds, after 10 minutes, there may be a further increase of pressure. Ignore it, as it indicates chemically bonded water.
  • If the displayed pressure is greater than 1.5 bar, a smaller sample should be used.
Maximum humidity in maxit floor products for floor coverings                             To Top

  Type of floor covering material

Cement-based
Floor product

Calcium Sulphate-based Floor product

Unheated Floors
Floor 4150/4310/4360
  • tiles, carpet, PVC
  • parquet, laminates



3,5%
3,0%



0,5%
0,5%

Heated Floors
Floor 4150/4310/4360
  • tiles, carpet, PVC
  • parquet, laminates



3,3%
2,8%



0,3%
0,3%

Self-drying products
Floor 4160/4320/4360
  • Tiles after 1 day,
  • PVC and carpet after 3 days
  • Parquet and laminates after 7 days
 

Critical Issues                                                                                                         To Top


Although the test can be carried out on construction site, there are some critical points to watch out for:
  • Representative sampling
  • Temperature during preparation and testing (avoid cold temperatures < 5° C because of condensation)
  • Crushing and milling grade (not too fine, because of temperature effect)
  • Temperature on site which influences the measurement.

However the method is still often used on site and gives reliable results.

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