Rising Damp or Condensation a Common Misdiagnosis?

I've written before about the incorrect diagnosis of rising damp, for problems such as salt contamination. It's a common mistake made by surveyors even those considered experienced. Its often because to determine exactly what is happening requires some element of intrusive investigation and analytical diagnosis. Most surveyors normally stop at this point providing only a non-invasive survey or simply don't have the expertise and equipment to undertake the necessary diagnostics.?

Here you can read my article about just how easy it is for salt contamination to be misdiagnosed as rising damp.

There are however other common damp problems which are also misdiagnosed as rising damp. Yes, I'm talking about condensation.

Condensation is also a form of dampness which particularly at this time of year is misdiagnosed as rising damp. Why, well to the untrained and inexperienced symptoms can be similar.

Condensation symptoms often confused as rising damp are:

1: Dampness to the base of the wall.

2: High moisture levels in the skirting boards.

3: Damage to the plaster and decorations (in extreme cases).

Contrary to the belief in many cases where condensation is a severe problem mould isn't always visible, this is because the walls are simply too wet.

If the problem is caused by condensation then moisture will 'normally' only be found in or on the surface plaster, the masonry behind the surface will 'normally' be dry. There are however some exceptions; 1: where condensation is a severe problem or 2: where condensation forms upon sub-floor walls above the damp proof course causing rising damp symptoms.

If you're using an electronic moisture meter to assess the surface for dampness, in either scenario you may obtain high readings. If condensation is or has recently been a problem but the surface isn't wet to the touch, you may still obtain high readings if the plaster has been dampened . The profile may also appear similar too, as in most cases, it is the base of the wall which is cooler and therefore most susceptible to condensation thus, falsely creating the illusion of rising damp.

Illustration drawing highlighting the effects of surface moisture condensation dampening the plaster.

Airborne moisture is attracted towards the surface of the material by vapour pressure and temperature.

Elevated readings taken from both the surface plaster and skirting boards, so is it rising damp or condensation?....

Struggling to tell the difference?

There are a few basic observations which can help establish the difference between a rising damp and condensation problem. Even to the most novice surveyors, these should be obvious with just a little knowledge and equipment.

1: Moisture on the surface of the material is not a symptom of rising damp.

2: Mould is not a symptom of rising damp.

3: Providing the building has no history of structural dampness with a condensation problem there should be no salts.

4: With a condensation problem there should be no distinguishable salt band (this can usually be found using an electronic moisture meter).

5: If condensation is the result of sustained high humidity there will likely be symptoms else where in the property too.

6: If condensation is the result of temperature or restricted air movement there will usually be obvious indications such as;

a: imprints on the floor coverings where furniture has been positioned against the surface.

b: The orientation of the building can be established to determine the risk (north is cold and vulnerable)

c: The temperature of the surface can be established (using a thermometer / thermal imaging camera)

d: The presence of insulation can be established (cavity wall or surface insulation)

Furthermore, a unique difference between the two is the profile that can be obtained from the wall using an electronic moisture meter. A condensation profile will gradually diminish rather than a sharp cut off which occurs in a rising damp scenario.

Typical condensation profile determined with an electronic moisture meter

Typical condensation profile determined with an electronic moisture meter

Typical rising damp profile determined with an electronic moisture meter

Following on from the above observation stage, your next step to establishing the difference between a condensation and rising damp problem should be to establish the walls risk to condensation.

To do this you'll need to understand the relationship between the wall and the air. You can do this using a simple diagnostic App like the 'Colemanator' .

The Colemanator is a very simple yet clever Application which will provide an assessment of the Indoor Air Quality and calculate the psychrometric properties of the air, as well as the 'risk to surface moisture condensation' and 'mould growth'.

Using a hygrometer obtain the temperature and humidity of the air, then using a surface thermometer measure the temperature of the surface of concern. Enter these parameters into the Colemanator App and the App will automatically determine the risk of condensation and mould.

The App will also establish the dew point temperature of the air and together with knowing the surface temperature of the material evaluate the risk of condensation.

Psychrometric properties of the air calculated by the Colemanator App

Dew Point Explained

When the air reaches its maximum holding capacity of water vapour at a specific temperature, we refer to the air as ‘saturated’. Cooling the air causes the excess water vapour to be dropped as liquid water; this process is referred to as condensation. By evaluating the relationship between the air temperature and the surrounding surface temperatures we can establish when condensation might occur. The temperature at which condensation is determined is variable to the atmospheric conditions and is referred to as the ‘dew point’.

Using the Colemanator App will help you establish if indeed there is a risk of surface moisture condensation although some interpretation of the results maybe needed if the conditions weren't favourable at the time of inspection however, could be at other periods of the day particularly at night when it's usually colder.

Intrusive investigations

Another way to distinguish between possible condensation and rising damp is to undertake some minor invasive investigations (you should always seek permission from the homeowner prior).

As mentioned above, "If the problem is caused by condensation then moisture will 'normally' only be found in or on the surface plaster, the masonry behind the surface will 'normally' be dry."

Therefore using deep wall probes provided with most moisture meters will allow you to assess the material beneath the plastered surface. To do this simply drill two small 5.5mm holes about 30mm apart through the plaster and into the masonry. The probes are insulated along their length as such, they will only take a reading from the exposed tip. Place the probes into the holes and take a reading from structure behind the plaster. If the readings are low and lower than those obtained directly from the plaster material itself, the structure behind is dry. The cause of the surface readings was likely surface moisture condensation.

Low readings obtained from the structure behind the damp surface plaster indicating the wall is dry.

Illustration detail highlighting the use of deep wall probes to measure behind the surface material

If necessary you could also remove a sample of material from the wall and analyse this chemically for its moisture content using a calcium carbide / speedy meter. This process involves mixing a known weight of sample material with a reagent which reacts with the moisture present in the sample. The reaction produces acetylene gas proportionate to the amount moisture and a sealed vessel is used to measure the build-up of gas thus, providing the moisture content of the sample material. Again, if the problem were surface moisture condensation, expect a low reading.

Example of a low calcium carbide reading indicating the sample taken from the structure is dry.

I hope this article has gone some way in explaining just how easy it is for surface moisture condensation to be confused with rising damp however, when armed with just a little knowledge and equipment it is easy to differentiate between the two.

Finally, if you've made it this far, I hope you found this article useful.

Thanks for taking the time to read it and if you have any questions or queries please don't hesitate to get in touch.

Happy surveying

Russ

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If you would like to learn more about damp diagnosis or surveying you may?also find the following articles useful:

Rising Damp Explained, everything you thought you knew, a little bit more and a few of my opinions!

Independent damp surveyor vs Contractor damp surveyor, which is best?

The truth about Moisture meters (Protimeter / Tramex / Flir)

Russell Rafton - Dryfix Preservation Ltd Senior Surveyor

Dryfix Yorkshires Leading Damp & Timber Specialists

A 6 x Industry Award Winning Company with the Property Care Association.