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Damp Diagnosis: Calcium Carbide Meter – ‘Speedy Meter’

June 11th, 2012

All posts, Damp / Rising Damp / Damp Proofing /, Surveying

Calcium Carbide Meter – ‘Speedy Meter’

A calcium carbide meter is another moisture testing device used to aid surveyors in damp investigations and diagnosis.  Performing a calcium carbide test is however disruptive and for this reason these test are usually avoided in damage limitation surveys such as, pre-purchase inspections unless permission is granted prior. This does not mean the use of these meters in a pre-purchase scenario is avoided totally. The surveyor will often report his finding using an non destructive form of testing  such as an electronic moisture meter for the purpose of the report and then recommend a further intrusive investigation is undertaken using either a calcium carbide meter or laboratory analysis prior to concluding their findings.

So What is a calcium carbide meter?

A calcium carbide meter is a sealed vessel which is used to mix measured samples of masonry with calcium carbide.  Calcium carbide will react with moisture present within the material and produce acetylene gas. The proportion of gas released is directly proportionate to the amount of moisture present in the material therefore by measuring amount of gas we can derive the total Moisture Content (MC) of the material tested.  The flask has a calibrated gauge which is used to measure the pressure excreted in the cylinder by the accumulation acetylene gas which is read as moisture content.

Does this mean the results of a calcium carbide meter are conclusive?

Although unlike an electronic moisture meter a calcium carbide meter does give a quantitive result of the amount of moisture present, it can only measure the total volume of moisture and cannot distinguish between hygroscopic moisture and free moisture.

The British Research Establishment Digest BRE 245 ‘Rising damp in walls; diagnosis and treatment’ recommends “To obtain conclusive proof of the presence of rising damp” by comparing the hygroscopic moisture content (HMC) with the Moisture Content (MC) of a material sample as found.

Hygroscopic means the ability of a substance to attract and hold water molecules from the surrounding environment , this is achieved through absorption. Hygroscopic materials will naturally achieve equilibrium moisture with the surrounding environment, the more saturated the air, the more moisture absorbed by the material. The hygroscopic moisture content can however, also be influenced by contaminates within the material which are also hygroscopic such as salts which can lead to erroneous results.

The Moisture Content (MC) of a material is the combination of hygroscopic moisture in addition to additional free moisture from other sources such as rising damp, penetrating damp or water leaks.

By knowing a materials natural hygroscopic moisture content in a dry state we can conclude additional moisture contributing to it’s overall moisture must have arrived from another source.

As previously mentioned however, a calcium carbide meter will not differentiate between fee and hygroscopic moisture it will only determine the materials total volume of moisture.

In this scenario readings taken using this instrument can also be misleading to the untrained. It is however possible to achieve more accurate results using a calcium carbide meter by taking multiple samples from the same material. This can be performed by profiling a wall taking readings at intervals upwards measuring the total volume of moisture distributed through the wall (see picture). In combination with salt analysis tests, allowances can be made for hygroscopic salt contamination.


Building materials do however vary in porosity and their ability to hold moisture, therefore it is not possible to take comparative readings using a calcium carbide meter from different materials. The BRE mention in digest 245 “if the found moisture content (MC) is less than 5% at the base, it is unlikely that the wall is severely affected by rising damp” This 5% figure is merely a guide and refers to the base of the wall above damp proof course level. It does not suggest readings recorded above 5% are an indication of rising damp, it emphasises the importance of testing HMC and MC, as some materials especially when contaminated with salt can hold above 5% MC even when in a dry condition.

Overall the calcium carbide meter is an excellent tool to aid surveyors in damp investigation and diagnosis,  It will however not provide conclusive results or determine the origin / cause of the problem. Again this tool when used on site should also be accompanied by salt analysis to determine the presence of hygroscopic salt contaminates, and must never be used to compare two different materials for comparison. For conclusive results between a materials hygroscopic moisture content and its free moisture laboratory analysis should be used.

Provided calcium carbide meters are used by a trained and qualified surveyor who knows how to use them properly they do provide in depth investigation tool for moisture profiling and determining quantitive moisture levels in masonry.

Our damp and timber reports are only undertaken by experienced and fully qualified surveyors who hold the National Qualification for remedial surveying C.S.R.T. awarded by the BWPDA / PCA, our industry body. This proves that our surveyors have been independently examined and tested, proving their extensive knowledge and expertise.

All of our surveys are carried out in accordance with The British Standards Code of Practice.

Our surveyors carry all the necessary diagnostic and inspection equipment onsite, including thermal imaging and fibre-optic cameras to examine hidden cavities, highlighting blockages and bridged damp proof courses. Salt analysis testing and equipment for in-depth moisture analysis of masonry walls and plaster is also available. Photographic evidence of our findings is recorded and included within our report, so you can be sure of correct diagnosis.

Our reports contain comprehensive advice of any problems identified and include our recommendations, specifications and costs for repairs, if necessary. Edited pictures along with category damage ratings are also included to assist your understanding about the urgency of any repairs needed.

Our reports are available in both printed media and/or converted into secure electronic Portable Documents (PDF) for email.

Suspect a Problem?

If you suspect a problem and require a survey, or need advice please Contact us.




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