Calcium Carbide Moisture Testing

Understanding Calcium Carbide Tests: Purpose and Procedure

As RICS Chartered Surveyors, we utilise Calcium carbide testing to provide an understanding of the potential Total Moisture Content of a particular aggregate or material.

This straightforward and effective testing method can be a useful tool in telling you whether part of a property is potentially “wet” or indeed, dry.

What is Calcium Carbide?

Calcium carbide (CaC₂) is a chemical compound that reacts with water to produce acetylene gas and calcium hydroxide.

The reaction is the fundamental basis for the calcium carbide test.

The amount of gas produced is directly related to the moisture content in the material being tested, making it a relatively reliable indicator.

How to Perform a Calcium Carbide Test

Materials Needed:

  • Calcium carbide powder.
  • Moisture testing vessel.
  • Scale for measuring the sample.
  • Protective gloves and goggles.

Procedure:

  1. Sample Preparation:
    • Collect a sample of the material you wish to test: in most cases, our RICS Chartered Surveyors will be using a drill to slowly collect a sample of masonry or plaster.
  2. Weighing the Sample:
    • Weigh the sample in accordance with your particular vessel.
  3. Adding Calcium Carbide:
    • Place the sample into the moisture testing jar lid, paying particular attention to not allowing the agent to come into contact with the sample.
  4. Sealing the Jar:
    • Seal the vessel and then allow the sample and reagent to mix.
  5. Waiting for Reaction:
    • Allow the reaction to proceed for a few minutes and await results.
  6. Reading the Results:
    • After the reaction stabilises, the pressure gauge to the front of the vessel will present a reading of Total Moisture Content.
  7. Calculating Moisture Content:
    • It is important to remember that calcium carbide testing presents a reading for the Total Moisture Content and is, therefore, more reliable at telling you something is dry, as opposed to it being wet.
    • If you encounter a high Total Moisture Content reading (let us say a reading of 14% wet weight on the pressure vessel) then the next stage of assessment would be to collect a further sample for Gravimetric Testing.
    • If the reading is low, then you can opine that the sample is dry.

Conclusion

Calcium carbide tests are an essential diagnostic tool for any Surveyor seeking to identify and diagnose structural moisture.  It is impossible to determine the moisture content (wet and dry) of building fabric without doing so.  Our RICS Chartered Surveyors utilise Calcium Carbide Tests to support Part 35 Expert Witness Reports.

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