Sampling Buildings for Moisture and Salt Analysis

Earlier last week a Linkedin post queried the accuracy of results from a calcium carbide meter (speedy meter) when samples were taken from the DPC proof course location.

Well, rightfully this query had some legitimate concerns. Irrespective of the damp proof course referred to in this case being retrofit, taking samples directly from the damp proof course position is not advised. As you know a damp proof course is designed to protect the masonry above from moisture, as such moisture will be present in the masonry up to the location of the damp proof course. Taking a sample for analysis directly from this location will almost inevitably yield elevated results as material from both above and below the DPC will be extracted when the sample is taken. In addition, taking a sample from this location if the damp proof course is physical i.e bituminous or pvc will almost indefinitely damage / perforate the material. So, this is not advised.

THE REALITY OF INTRUSIVE INVESTIGATIONS

You’ll often see building reports advising that moisture / salt analysis samples should be undertaken for accurate and conclusive proof of a damp problem and its origins, however in reality this is something very rarely followed up. I believe this is due to combination of; a lack of people capable of undertaking sampling properly but also the lack of expertise in interpretating the results. In addition whist many companies / people market themselves as ‘damp specialists’ in reality there are very few that actually provide who provide evidence by means of sampling to support their diagnosis, most is based upon assumption, guesswork and often incorrect interpretation of electronic moisture meters.

THE CALCIUM CARBIDE METER vs GRAVIMETRICS

The calcium carbide meter is a great piece of equipment which unfortunately gets a lot of bad publicity due to it’s inability to differentiate between free and hygroscopic moisture. Whilst this is true and the carbide meter does have it’s disadvantages, the only quantitative alternative is gravimetic analysis, yet, despite the advantages of gravimetrics there are very few people in the industry with the equipment and knowledge to perform gravimetric or chemical salt analysis. The reason for this is simple, gravimetrics requires the use of a laboratory and expensive equipment, the the process is also time consuming, disruptive and requires an in depth knowledge along with a scientific and methodical approach which is not very well shared.

So, if you’re a surveyor and you don’t have access to a scientific laboratory or the skills to undertake gravimetric and chemical salt analysis then the speedy meter (calcium carbide meter) should really be your next best asset.

FORGET ABOUT WHAT YOU'VE BEEN TOLD, SPEEDY METERS ARE GREAT!

Before i became involved in gravimetrics, for over 15 years I used my speedy meter almost daily and I still do under many circumstances where I need results fast or where there is an absence of contamination thus, less risk of hygroscopic moisture. Remember there are many forms of dampness and hygroscopic contamination is usually only present in a few or in old buildings with a history of damp . We survey buildings for much more than just rising damp, so surveying problems in new builds, flood / water damage incidents and even distinguishing between structural moisture and condensation are often ideal circumstances to use a carbide meter.

HOW TO GET MORE FROM YOUR SPEEDY METER

Here are a few of my tips to help you utilise your carbide meter more and ensure your sampling regime is consistent and more reliable.

If however, you do find yourself in a position where you need more information and don’t have a gravimetric laboratory then don’t panic, as long as you have the ability to take the samples, please feel free to send them to me and i’ll happily undertake the analysis for you.

HOW TO GET THE MOST FROM YOUR CALCIUM CARBIDE METER (SPEEDY)

DISRUPTIVE SAMPLING FOR MOISTURE / SALT ANALYSIS

Before you start here’s what you need.

1.      Buy your self some sealed container pots to place the sample in (I like to use old 35mm film canisters as these are small and air tight)

2.      Ensure you have a percussion hammer drill and a fresh sharp drill bit 12mm.

3.      If you’re taking multiple samples in quick succession ensure you have a number of fresh new drill bits that you can rotate to prevent overheating and drying the samples during the process of extraction.

4.      You’ll also need something to catch the samples in, something non-moisture absorbent. I have gauge dish or use a laminated card.

THE SAMPLING PROCESS

5.      Before you start profile the wall using a non destructive device (electronic moisture meter) to establish your expected moisture profile.

6.      Establish the vertical increments that you’re taking the samples from usually anywhere between 100mm - 200mm is acceptable.

7.      Mark the profile and the readings taken either on the wall or use a ruler / gauge aside to ensure samples are taken from the correct location.

8.      Scan the wall for buried / hidden services

9.      Personally I proffer to chase the plaster from the wall first allowing me to identify the materials in the walls construction (brick, stone and mortar). I then sample from the same material consistently and sometimes i’ll sample the plaster separately too. The mortar is likely to be the most consistent material used in the walls construction as such, i mostly sample the mortar. The mortar is normally the conduit for moisture where hard /dense brick or stone is used in the walls construction.

10.  Slowly rotate the drill to extract the sample from the wall. Ideally your should be extracting material from around ? - ? way through the wall.

11.  Place the sample in a sealed container and either process on site with your carbide meter or send away for gravimetic analysis ASAP. 

If you're processing onsite using a carbide meter and you're worried about the influence of hygroscopic contamination affecting your results, then perform a simple onsite salt analysis test using left over sample and a protimeter salt analysis kit (link below). This won't provide you with quantitative measurement of how much contamination is present however, will allow you to identify the presence of ground water salts thus a risk of contamination and an understanding to the variations in your results.

https://www.yorksurvey.co.uk/protimeter-salts-analysis-kit-c2x22486749

Furthermore, as construction materials vary in their air dry moisture content thus making it difficult to put an exact figure on what moisture content percentage is considered dry, take a separate sample from an area unaffected and use this as baseline or established dry goal. You can then compare the results from your profiling regime to the considered dry reading.

I hope you found this article useful and informative and I hope atleast hope I now see many more posts on linkedin where calcium carbide meters are featured with less negativity.

If you have any questions or queries about these subjects please don't hesitate to get in touch.

Happy surveying

Russ

If you would like to learn more about moisture mapping or damp diagnosis you may find the following articles useful:

Moisture Content Analysis - https://www.dryfix.net/blog/explained-moisture-content-analysis-using-the-gravimetric-process/

Calcium carbide Meters Explained - https://www.dryfix.net/blog/damp-diagnosis-calcium-carbide-meter-speedy-meter/

Moisture Mapping Explained - https://www.dhirubhai.net/pulse/moisture-mapping-ideal-article-damp-specialists-water-russell-rafton-/

Russell Rafton - Dryfix Preservation Ltd Senior Surveyor

Dryfix Yorkshires Leading Damp & Timber Specialists

A 4 x Industry Award Winning Company with the Property Care Association.

www.dryfix.net