Mildew stains and saltpetre on walls: Causes, moisture and permanent solutions

Introduction

If you live in an older building or have damp cellars, you may have already been confronted with two common problems: Mould stains on walls and so-called saltpetre on walls. These phenomena are not only unattractive to look at, but can also have serious consequences for the masonry and your health. In this article, you will learn all about the causes of these problems, the dangers of damp and how you can permanently eliminate them. A moisture meter can help to detect moisture in walls at an early stage and thus prevent mold.

What are mold stains on walls?

Mould stains - also known as mildew stains - are dark, usually greenish-black or brownish discolorations that appear on damp walls. This is mold infestation that forms and spreads on damp surfaces. The initial stage of mould stains can often be recognized by small spots of discolouration, which can develop into larger areas over time.

In the initial stages, mildew stains are sometimes difficult to distinguish from ordinary dirt. However, a typical characteristic is that they return again and again despite cleaning, as long as the cause - the moisture - is not removed. Contact with these substances can cause health problems, especially for allergy sufferers and people with respiratory diseases. To accurately determine the moisture in the walls, the use of a moisture meter is essential.

What is saltpetre on walls?

What is commonly referred to as "saltpetre on walls" is actually salt efflorescence or, more precisely, lime efflorescence. These white, powdery deposits form on walls that are affected by rising damp. Nitrates, which enter the masonry through the oxidation of organic substances, can also contribute to this efflorescence and cause damage even in small concentrations.

As explained in the Isofin manual, the term "saltpetre" originated historically through a mix-up: the white efflorescence on walls looks similar to the saltpetre used to make black powder. In reality, however, it is usually lime deposits that occur when water moves through the masonry, dissolving lime from the mortar and transporting it to the surface, where it remains after the water has evaporated. It is important to use a moisture meter to identify the exact problem areas in order to effectively combat the damaging effects of moisture.

Causes of mildew stains and saltpetre on walls

Causes of mildew stains on walls

The main cause of mildew stains on walls and mold infestation is always moisture. This can have various sources:

  • Rising damp from the ground if the horizontal barrier in the masonry is missing or defective
  • Transverse moisture penetration with inadequate vertical external sealing of the walls
  • Condensation due to insufficient thermal insulation or inadequate ventilation in the living space
  • Water damage caused by leaking pipes or roofs that soak the masonry
  • Building moisture in new buildings that have not yet completely dried out

In addition to moisture, molds need nutrients for their growth, which they find in the form of organic materials such as wallpaper, paint, wood or even house dust. The optimum growth conditions for mold are at temperatures between 20°C and 30°C and a relative humidity of over 70% on the walls.

Causes of saltpetre on walls

Saltpetre efflorescence is mainly caused by:

  • Capillary moisture: As explained in detail in the Isofin manual, water rises from the ground through the capillaries of the masonry. In doing so, it dissolves minerals (especially lime) from the mortar. This efflorescence often occurs in conjunction with existing moisture damage.
  • Missing horizontal barriers: Especially in older buildings built before around 1930, effective horizontal barriers are often missing, which leads to permanent damp in the walls.
  • High salt content in the masonry: This can be caused by road salt, natural soil salts or historical use of the building (e.g. as a stable). Sulphates that get into the masonry through rain can also cause damage, especially if they occur in high concentrations.

The Isofin manual describes the process very clearly: "The water penetrating the wall dissolves small amounts of lime from the masonry mortar, which consists of a mixture of lime and sand, during its capillary transport. The capillaries transport the lime water to the wall surface, where the water evaporates and leaves the lime behind as a fine, white deposit." Nitrate salts can be activated by moisture, particularly in cellars, and lead to plaster damage. A precise measuring range is crucial for the accuracy of moisture measurements, especially when diagnosing damp walls.

Measure and detect moisture

Moisture in walls can be caused by various factors. Common causes are cold bridges, which lead to condensation, and problems with air circulation, which do not remove the moisture sufficiently. Incorrect heating and ventilation or structural damage such as leaking roofs or pipes can also lead to damp problems. In order to determine the exact cause of the moisture, the use of a moisture meter is essential. This tool helps to measure the moisture content in the wall and identify the source of the problem.

Measuring moisture - methods and devices

Moisture can be measured in different ways, depending on the type of moisture meter used. Capacitive moisture meters work with electric fields to determine the moisture content, while resistive moisture meters measure the electrical resistance in the material. It is important to select the right moisture meter for the application in order to achieve accurate measurement results.

A moisture meter has been specially developed for measuring moisture in building materials. With this device, you can regularly check whether your measures against moisture are successful or whether further steps are necessary. Moisture meters provide a reliable method of monitoring the moisture content in masonry and detecting potential problems at an early stage.

Masonry and moisture

Moisture in masonry is particularly problematic, as it acts like a sponge and can absorb and store water over a long period of time. The pore structure of the masonry favors the capillary transport of moisture. With a high-quality moisture meter, the actual moisture content in the masonry can be determined precisely, which is crucial for planning renovation measures. Modern moisture meters can distinguish between surface and deeper moisture in the masonry.

Are mold stains dangerous? The health risks of damp and mold

The question "Are mildew stains dangerous?" must be answered with a clear yes. Mildew stains or mold can cause serious health problems:

  • Respiratory problems: Mold spores can trigger or aggravate allergies, asthma and chronic bronchitis.
  • Allergic reactions: Skin rashes, irritated eyes and sneezing attacks are common allergic reactions to mold spores.
  • Infections: Certain types of mold can cause infections in people with weakened immune systems.
  • Toxic reactions: Some mold species produce mycotoxins that can cause neurological problems and other health complaints with long-term exposure.

Particularly at risk:

  • Young children and the elderly
  • People with a weakened immune system
  • Allergy sufferers
  • People with chronic respiratory diseases

The health risks are still comparatively low in the early stages of mildew stains, but increase as the infestation spreads. It is therefore important to remove mildew stains on damp walls as soon as they are discovered and, above all, to eliminate the cause of the damp.

Dangers of saltpetre for masonry

While saltpetre is less of a problem for human health than mold, it poses a serious threat to masonry. The Isofin manual describes this process in great detail and points out that untreated efflorescence of saltpetre can result in plaster flaking and ultimately the destruction of the building material:

"The lime efflorescence trickling onto the cellar floor is not only annoying because you have to constantly sweep it up, but also shows the expert that the masonry is subject to slow but constant decay. This is because the lime comes from the mortar, in which it serves as a binding agent for the sand. If lime is constantly dissolved from the mortar and transported away, the mortar becomes increasingly poorer in binding agents and loses strength." Various building materials such as concrete, bricks or plasterboard can be affected by saltpetre, which illustrates the versatility and extent of the problem.

This process can be self-reinforcing:

  1. The loss of lime leads to larger pores in the mortar
  2. Larger pores enable higher water transport
  3. The higher water transport dissolves even more limescale
  4. The pores become even larger and so on

The end result is what experts call "structural decay due to mortar compression": The mortar can no longer support the weight of the house. The joints are compressed and the bricks lose their hold. This damage can jeopardize the stability of the entire building in the long term. Special moisture meters are used to measure this damage, which can also measure the salt content in the masonry.

Effective solutions: Removing mildew stains from damp walls

How can you remove mildew stains from walls?

There are various approaches to removing mildew stains from walls:

  1. Superficial treatment: In the case of light infestation, mildew stains can be treated with special mold removers. However, this is only a temporary solution if the actual cause of the damp is not eliminated. Before remediation, measuring the moisture with a moisture meter is crucial in order to assess the level of moisture in the walls and plan suitable measures.
  2. Eliminating the cause of the damp: For a permanent solution, the cause of the damp must be eliminated:
    • In the event of rising damp, a horizontal barrier can be created using products such as Isofin
    • If there is no vertical external waterproofing, either an external waterproofing or an Isofin surface barrier can be installed
    • If there are condensation problems, the insulation should be improved and the ventilation behavior adjusted
  3. Restoration of infested walls: Heavily infested materials such as wallpaper, plasterboard or plaster should be removed and replaced. It is important that the new materials are only applied after complete drying.

The right approach to refurbishment

The following procedure is recommended for the successful renovation of damp walls:

  1. Moisture analysis: First of all, the exact cause of the moisture should be determined. This can be done by measuring with moisture meters as described in the Isofin manual. It is important to obtain correct readings in order to precisely localize the problem areas in the masonry.
  2. Eliminating the source of moisture: Depending on the situation, various measures can be taken:
    • Installation of a horizontal barrier against rising damp in the masonry
    • Creation of a vertical external seal or Isofin surface barrier
    • Improve room ventilation and thermal insulation to avoid condensation moisture
  3. Drying out: After waterproofing, the wall must be allowed to dry out completely. As emphasized in the Isofin manual, this process can take several months depending on the wall thickness and environmental conditions. Measuring the moisture with a moisture meter helps to monitor the progress of drying.
  4. Remediation of infested surfaces: Only after complete drying should infested surfaces be remediated, for example by:
    • Removal of the old, affected plaster
    • Application of new, open-pored plaster
    • Use of diffusion-open paints and wallpapers

Remediation of saltpetre on walls

A systematic approach is required to remediate saltpetre on walls:

  1. Remove saltpetre: First, the salt efflorescence should be brushed off dry. A damp wipe would only transport the salts deeper into the masonry. These crystalline deposits on the wall surface are an indication of moisture problems. It is important to use a moisture meter to accurately determine the moisture content in the masonry and to check the effectiveness of the remedial measures.
  2. Prevention of capillary water transport: As the Isofin manual explains in detail, it is crucial to prevent capillary water transport. This can be achieved with a horizontal barrier in the base area of the masonry.
  3. Isofin application: The manual describes in detail how to create an Isofin lock:
    • Drill holes with a diameter of 10-12 mm are drilled into the wall at intervals of 25 cm
    • Isofin bottles with injection caps are inserted into the drill holes
    • The masonry absorbs the Isofin automatically
    • A water-repellent zone forms in the masonry within about a week
  4. Wait for it to dry out: After treatment, the wall must dry out completely. As the manual emphasizes: "You therefore do not need any additional agents or measures to support the waterproofing effect." You can objectively check the drying progress with a moisture meter.
  5. Application of suitable materials: After drying out, only materials that are open to diffusion should be used. The manual recommends lime plaster in particular, which is "naturally mold-repellent".

Preventive measures against mildew stains and saltpetre on walls

Prevention of mildew stains on walls

The following measures should be taken to prevent mildew stains from forming on walls and to avoid a poor indoor climate:

  • Regular ventilation: airing out rooms several times a day reduces the humidity indoors.
  • Constant room temperature: Avoid large temperature fluctuations, which can lead to condensation on the walls.
  • Furniture at a distance from the wall: A distance of at least 5-10 cm from the wall allows air to circulate and prevents moisture build-up.
  • Monitoring humidity: A hygrometer can be used to check the relative humidity, which should ideally be between 40% and 60%.
  • Professional waterproofing: In older buildings, professional waterproofing against rising damp in the masonry can be useful.
  • Regularly measure the moisture: With a moisture meter, you can monitor critical areas on the walls and intervene at an early stage.

Prevention of saltpetre on walls

The following measures are recommended to prevent saltpetre efflorescence:

  • Professional waterproofing: In new buildings, attention should be paid to professional horizontal and vertical waterproofing. In the case of old buildings, a horizontal barrier can be retrofitted to the masonry.
  • Use of suitable building materials: Salt-resistant plasters should be used for renovation work.
  • Regular inspection: Inspect the cellar walls for the first signs of efflorescence or moisture.
  • Drainage systems: If the groundwater table is high, a drainage system around the building can be useful to keep moisture away from the masonry.

FAQ about moisture in walls

Here are some common questions about moisture meters and moisture in walls:

  • What is a moisture meter? A moisture meter is a device that measures the moisture content in various materials such as walls, wood and concrete.
  • How does a moisture meter work? Moisture meters work either capacitively, by using electric fields, or resistively, by measuring the electrical resistance in the material.
  • What types of moisture meters are there? There are capacitive and resistive moisture meters as well as special moisture meters for different applications.
  • How can I measure the moisture in a wall? Moisture can be measured with a moisture meter by holding the device against the wall or inserting it into the material.
  • What are the typical causes of damp in walls? Typical causes can be cold bridges, air circulation problems, incorrect heating and ventilation and structural damage.
  • How can I dry damp walls? Damp walls can be dried by improving ventilation, using dehumidifiers and removing the source of moisture.
  • What are the consequences of damp in walls if left untreated? Untreated damp can lead to mold, structural damage to masonry and health problems.

Conclusion: Sustainable solutions for permanent dryness on walls

Mould stains and saltpetre on walls are not just aesthetic problems, but serious indicators of moisture problems in the masonry. If they are ignored, they can lead to health problems and considerable damage to the building fabric.

The sustainable solution is not to treat the symptoms superficially, but to eliminate the causes - the moisture in the masonry. As the Isofin handbook emphasizes: "Important: Never hide moisture in the masonry by blocking the evaporation surface, but always block the entry of water into the material."

With modern sealing systems such as Isofin and regular measurement of moisture with moisture meters, permanent solutions against moisture can also be implemented in older buildings, which both protect the masonry and promote a healthy living climate.

If you are unsure whether the stains on your wall are mould stains or mildew or whether the white efflorescence is actually saltpetre, you should consult a specialist who can make an accurate diagnosis and recommend suitable remedial measures. If saltpetre efflorescence is discovered, urgent action is required to prevent long-term damage to the masonry.

Investing in professional refurbishment pays off in the long term - by preserving the building fabric, increasing the value of the property and, last but not least, creating a healthier living environment without damp and mold.