Salt Efflorescence’s Effects on Damp Meters

Salt effuesence on a building

While the signs of a damp issue are usually closely related (surfaces damp to the touch, water spots, condensation), there's one that stands out from others – salt efflorescence.

Dry, but damaging and unsightly, salt efflorescence can be as tricky a problem for property owners as it is for building surveyors. With the ability to interfere with a damp meter's measurements as well as be confused with another damp issue, salt efflorescence can be difficult to diagnose accurately.

In this article, we'll take a complete look at salt efflorescence in building inspections, covering:

  • A look at salt efflorescence
  • Salt efflorescence's effects on damp meters
  • Avoiding false-positive tests
  • Inspecting for salt efflorescence
  • & more


A Look At Salt Efflorescence

Salt Efflorescence on floorSalt efflorescence occurs when salts present in building materials of structures or the ground they're in direct contact with (think: basement floors) are drawn to a surface by moisture.

These salts can be naturally occurring, or they may have been added during the construction process. When damp evaporates, it leaves behind crystallized salt deposits on the surface of the material. Commonly found on brick walls and stone masonry, salt efflorescence can also affect other porous building materials:

  • Concrete
  • Cement-based stucco
  • Mortar
  • Wood
  • Plaster


How Problematic is Salt Efflorescence?

In the sense of, “is efflorescence harmful to human health?” not really. Touching the substance will not hurt a person.

However, salt efflorescence affects both the aesthetics and structural integrity of buildings. The white powdery streaks created by this process make surfaces appear stained or discolored, detracting from the overall appearance of a building's facade. In addition to its unattractive appearance, salt efflorescence can adversely affect mortar joints and brickwork by weakening them as salts accumulate in these areas over time.

Moreover, if left unchecked, salt efflorescence can corrode steel components and other building materials.



Salt Efflorescence's Effects on Damp Meters

Salt efflorescence can have a significant effect on the accuracy of moisture meters.

When salt efflorescence is present in these materials, it can skew the readings of a pin-type damp meter. As salts accumulate in a material's surface, they attract water molecules from the surrounding environment. Not only does this increase a material’s water retention, but it also makes water molecules present more conductive. 

During a reading with a pin-type meter (which measures moisture by measuring the electrical resistance between its probes), the presence of salt makes a material seem more inundated by moisture than it is. 

The problem of salt efflorescence affecting moisture meters is compounded by two factors: accumulation and masonry mortar

First, as more salts accumulate on a material's surface over time, their ability to attract water molecules also increases – resulting in even more inaccurate readings from a damp meter

Second, the mortar used in masonry construction often contains higher levels of sodium than other building materials – meaning that areas with masonry are particularly prone to high levels of salt efflorescence.

How to Measure Moisture in Buildings - Protimeter


Similar, Yet Different | Rising Damp

Salt graphic Salt efflorescence and rising damp are two common forms of moisture damage that can occur in buildings. Closely related, they have a near identical presentation on building materials. They're often confused for one another, similar to how rising damp is sometimes mistaken for condensation.

Like salt efflorescence, rising damp occurs when moisture rises up through a wall from the ground below via capillary action. This phenomenon is caused by porous materials such as brickwork or plaster allowing moisture to penetrate into the building fabric. This often leads to visible signs of dampness and deterioration on internal walls – including salts left behind when the moisture evaporates. 

Rising damp usually manifests itself as a white discoloration & salt efflorescence near the floor or base of a wall. It can also cause wallpaper to peel, woodwork to decay, and paint to bubble and blister.

The key distinguishing factor between the two is height. Rising damp will never present itself higher than 1 meter from the floor in a space because of vapor pressure. 


Avoiding False-Positive Tests

Given its impact on moisture survey readings, the best way to avoid issues with salt efflorescence during a moisture survey is to accurately identify its location in a space or structure.

A moisture survey should include careful visual inspection of external walls and interior masonry, paying particular attention to any signs of discoloration or other surface damage caused by moisture penetration.

It’s also important to take into account factors such as the age of the building and local environmental conditions that may contribute to the presence of salt efflorescence. 

In areas where there is a high concentration of saline in the soil or atmosphere (think coastal communities), or where buildings are located near a body of water, there is an increased risk for salt efflorescence. This should be taken into consideration when performing a survey.

If your pin damp test meter comes in contact with salt efflorescence, it is important to take measures to protect the device and ensure future accurate readings. First and foremost, it is imperative to clean off any salt residue on the device before continuing use. Thoroughly wiping probes with a water-dampened cloth or paper towel is sufficient for cleaning.

Beyond causing inaccurate damp meter readings at the point of contact, efflorescence resin left on a meter can spell other issues. Salt crystals on electrical contacts and components within the device can cause corrosion – damage that's irreversible.


Material Breakdown: Inspecting for Salt Efflorescence

Identifying efflorescence on internal walls is a straightforward process and can easily be incorporated into an initial visual inspection of a space.

  • Salt efflorescence on plastering manifests itself as a white, powdery substance that accumulates on the surface of the material. It looks like an accumulation of fine salt particles that have crystallized over time due to the presence of moisture. The powdery substance is often found in high concentrations around windows and doors, where dampness has become trapped in the walls or where water vapor has been able to penetrate through cracks in the plaster.  In more extreme cases, salt efflorescence can cause delamination, or it can cause areas of discoloration and staining on the surface of the plaster.

  • Salt efflorescence on painted walls looks like an accumulation of fine grains of sand. In more severe cases, it can cause delamination or other discoloration of the paint surface. These deposits may become more visible when viewed under certain lighting conditions, such as with a flashlight or during a sunny day when light reflects off the wall at various angles.

  • Salt efflorescence in brickwork and concrete looks much the same as other materials – a white or slightly off-white, powdery deposit.
    Left untreated, it becomes particularly problematic in brickwork as the breakdown of salt crystals causes mortar to become weaker and more porous, leading to structural damage over time. The same goes for concrete. In addition, the presence of these salts can decrease brick's internal cohesion and adhesion properties, making it more prone to spalling (flaking off) or crumbling.


Effervescence Against Efflorescence

A common and potentially damaging issue in buildings, salt efflorescence provides a unique set of challenges for building materials and damp meters – none of which should be overlooked.

With the ability to distort moisture readings and cause damage over time, it is important to identify and understand the signs of salt efflorescence in order to complete accurate surveys.


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