Can release mold without active moisture

Fritz Lucke Bauaustrocknungs GmbH

Molds are not left dry!

Molds are a natural part of our living environment. Your spores can be found almost everywhere, including indoors. They are usually harmless. However, if the mold concentration exceeds a certain level, it can lead to health problems for the residents. Molds need a lot of moisture to grow. Causes of increased humidity inside buildings can be:

a) direct entry of moisture, for example via:

- defective roofs (especially flat roofs), gutters and downpipes;
- cracks in the masonry;
- insufficient drying out after construction work;
- Water ingress due to burst pipes, flood disasters, etc.

b) Inadequate removal of increased room air humidity due to:

- improper heating and ventilation, especially in "airtight" buildings.
- Condensation (condensation) of air humidity in the area of ​​"cold" walls, which is a problem in some old buildings due to insufficient thermal insulation. Construction defects such as thermal bridges also lead to water vapor condensation along the damaged areas in new and old buildings.

The list shows that in addition to structural and physical defects, the residents also contribute to increased humidity in the building. Improper ventilation in connection with activities that generate a lot of moisture (showering, cooking, drying clothes, operating large aquariums, etc.) can increase the moisture in the building beyond the tolerable level. This becomes a problem especially when the buildings have been laboriously sealed to save energy.

Everyone can check the humidity in their home themselves. Even simple humidity measuring devices (hygrometers) give an orientation about the relative humidity in the room. In the long term, it should not exceed 65 - 70% in the room air (less in winter) and 80% directly along wall surfaces in order to reduce the risk of mold growth.

The natural exchange of air with the surrounding air is reduced due to the increased tightness of the windows etc. in complex renovated buildings. The moisture generated in the building must then be removed by increased ventilation. Only at the beginning is the installation of mechanical ventilation systems, i.e. technical systems, which are supposed to guarantee an adequate exchange of air at all times without increasing the loss of heating energy through ventilation during the heating season.

Molds - what is it?

“Mold” is a collective term for fungi that can develop typical fungal threads and spores. Molds form cell threads in the growth phase. These are usually colorless, so that the mold cannot normally be seen with the naked eye during this phase. Molds form “spores” to multiply and spread. These are often colored so that the mold infestation at this stage can also be seen with the naked eye (for example as black or yellow mold stains).

Indoor mold growth is mainly determined by three factors: humidity, nutrient supply and temperature.

Molds can use a variety of materials as breeding grounds, such as:

- various types of wood, chipboard
- paper, cardboard, cardboard (including plasterboard)
- Wallpaper, wallpaper paste
- Plastics, rubber, silicone
- carpets, adhesives for floor coverings

Mold growth can also occur in and on cement and concrete. Molds can also grow on materials that do not release any nutrients themselves if organic particles and dusts from the air have settled on them (for example on glass).

Mold can only grow on materials if a certain minimum moisture content is present. It is not the total moisture content of the material that is decisive, but only the “free” water available to the mushrooms. Mold can also grow on and in materials that are not visibly wet. A relative humidity of around 80% on the surface of the material is sufficient. Particularly good growth conditions are always found when condensation forms on or in the material.

Molds - only annoying or also harmful?

Numerous studies on the health effects of mold have found a connection between exposure to mold and respiratory problems. Spores and metabolic products of mold fungi, if inhaled through the air, can trigger allergic and irritating reactions in humans. However, none of these studies has so far been able to determine the concentration of molds in the air from which negative health effects can be expected.

It is assumed that basically all molds are able to trigger allergic reactions in susceptible people. In the case of allergies, the body's immune system does not defend itself against dangerous foreign substances (for example pathogens), but instead falsely defends itself against harmful foreign substances (such as pollen, components of food).

The first contact with the foreign substance (antigen) does not cause an allergic reaction, but the body prepares itself to fight the supposed pest by producing defense substances (antibodies). Such a person is said to be "sensitized".

Only after renewed contact with the foreign substance can allergic symptoms occur, in which a whole chain of reactions takes place in the body, at the end of which the typical symptoms of allergic reactions such as runny nose, sneezing, red eyes, skin rash, etc. appear. The symptoms most frequently described for mold exposure in the interior are unspecific, for example conjunctival, throat and nose irritation as well as cough, headache or fatigue. Infections by mold (mycoses) occur only very rarely and only in particularly susceptible, severely immunocompromised people. Allergic and irritant effects can come from both living and dead molds, while only living molds are capable of triggering infections.

Molds - The Hidden Problem

Molds often develop in secret. A musty, musty smell or the first dark spots on walls, ceilings or furniture indicate the existing problem. If there is a suspicion of hidden mold infestation, the affected rooms must be examined more closely. If necessary, cavities behind cladding, ceilings or walls must be exposed in order to reach the source of mold. Specially trained mold detection dogs are increasingly being used to identify hidden mold contamination or, better yet, to “sniff out” it. Because almost all molds release volatile organic substances into the room air, which a specially trained dog can smell. When using mold detection dogs, it should be borne in mind that although the dog marks a hidden mold infestation, this does not yet allow any statement to be made about the actual extent of the mold load and any possible health risk for the residents.

Another method is to determine hidden mold damage by measuring certain volatile metabolic substances released into the room air by mold. These so-called "MVOC" measurements are, however, controversial with regard to the informative value of the results. It is not always clear whether the volatile organic compounds measured are really all of microbial origin. The evidence of increased MVOC concentrations in the room air also says nothing about the health risk for the residents: Neither should a renovation decision be derived from the measurement.

The situation is clearer in the case of mold infestation that is already visible on the surface with the naked eye (for example behind cupboards, in wall niches, etc.). In the case of a larger infestation (with more than approx. 20-50 cm2 of the affected area, it is not necessary to first analyze how high the mold load is in the apartment and what types of mold are present in the individual case. Action should be taken immediately. If mold sources are discovered, the The causes of the mold infestation should be investigated. Only then should the infested area be properly renovated, whereby the causes must be combated in each case. First of all, it must be clarified whether a source of mold is present and what causes it may have (structural defects, incorrect behavior the user etc.).

Such an examination requires a high level of expertise and should be carried out by a qualified specialist. A simple schematic approach is highly problematic. The specific individual case is to be assessed in each case using all available information. Before carrying out complex microbiological examinations, an on-site inspection should take place. During this site inspection, the possible causes of mold exposure should be clarified and recorded in an inspection report. In addition, the inspection should clarify whether one or more sources of mold are present indoors. The exact extent of the damage and the health risk can be assessed by analyzing the room air, possibly house dust and / or contaminated materials. The analyzes should only be carried out by competent laboratories, as otherwise incorrect procedures in the measurements and misinterpretations of the results cannot be ruled out.

Important: When placing orders for mold measurements, make sure that the laboratories operate quality assurance measures and, for example, regularly and successfully take part in round robin tests. If you have any doubts about the “quality” of the laboratory, get help from the local health department or get advice from local consumer associations.

If you fear that there is a source of mold in your home that could affect your health, then you should definitely seek advice from your local health department or consumer protection center.

If you already suffer from health problems that you fear may be related to the growth of mold in your apartment, contact your family doctor, an environmental medicine center or the state medical association.

What to do if the mold is discovered

Finding a source of mold in the interior is not to be equated with an acute health risk for the room users. The extent of the health hazard depends on the intensity and type of damage as well as the sensitivity of the room users and can often not be precisely quantified. Mold growth in the interior is viewed as a hygienic problem - even without these precise dose-effect relationships - and should therefore not be accepted. The precautionary principle applies, according to which the stresses must be minimized (minimization requirement) before illnesses occur.

If the assessment shows that there is mold contamination in the interior, renovation should be carried out. Even small sources of mold in the interior must be removed for preventive health protection. A mold remediation without eliminating the causes does not make sense, however, since sooner or later a renewed mold growth is to be expected. It is therefore essential to clarify the causes of mold growth, in particular the question of increased ingress of moisture.

Mold in rental apartments

Mold growth in a rented apartment is considered a lack of rent. In practice, there is often a dispute about the causes and the question of who has to pay for the repair of the damage, which in the end often has to be decided by the court - after hearing an expert.

Since mold pollution in indoor areas is a hygienic problem and health problems cannot be ruled out, the damage should be repaired as quickly as possible for reasons of health care, if possible by mutual agreement between tenant and landlord. In the case of medical certificates of health complaints due to mold exposure, it is important that the diagnosis shows a plausible connection between the complaints and mold exposure.

Important: Our information cannot replace specific legal advice in individual cases. If there are any doubts about the legal situation and the existing rights and obligations, tenants and landlords should seek legal advice at an early stage. Advice centers such as tenants 'associations or house and landowners' associations can provide assistance here.

Fight the mold

If remedial measures cannot be started immediately, it must be checked whether the affected areas can be temporarily cleaned and disinfected - if possible without swirling dust, for example with 70% ethyl alcohol (ethanol) for dry surfaces and 80% ethyl alcohol damp surfaces.

Targeted ventilation and heating can reduce the humidity in the room and limit further mold growth. However, this measure only makes sense if mold spores that were already present have been removed in order to avoid high concentrations in the room air and the formation of secondary sources.

Increased ventilation and heating as well as moving the furniture away from outside walls (approx. 10 cm distance) can reduce the risk of falling below the dew point in hard-to-reach areas and thus prevent further mold growth. This measure also only makes sense if mold spores that were already present have been removed beforehand. The basic prerequisite for the success of a renovation is the removal of the causes that led to the occurrence of the mold growth. On-site damage must be repaired and the room users informed about how mold growth can be avoided in the future.

The renovation effort should be adapted to the extent of the damage and the type of use of the space. The following aspects, among others, play a role:

- size of the infested area
- Strength of the infestation (individual spots or "thick" mold coating)
- Depth of the infestation (superficially or also in deeper layers)
- Types of mold that occur (important for the risk of allergies and infection, some types of mold form toxic toxins)
- Type of contaminated materials (on room-side, quickly expandable materials or in the masonry)
- Type of use (storage room, living room, kindergarten, hospital)

With the help of these criteria, an overall assessment must be carried out with expert knowledge. The protective measures to be derived from this must then be formulated during the renovation.

Small-scale renovation work (for example only superficial infestation, infested area no larger than about half a square meter, no structural defects), which are not expected to pose a risk to healthy people, can generally be carried out without the involvement of specialist personnel, whereby professional advice must be obtained . Smooth surfaces (metal, ceramic, glass) can be removed with water and normal household cleaning agents. Infested porous materials (wallpaper, plasterboard, porous masonry, porous ceiling cladding) can be cleaned with difficulty or not at all, as the mold growth can also have penetrated deeper layers of the material. Infested plasterboard or light partition walls should therefore preferably be removed. On non-removable building materials, it must be ensured that molds are completely removed (i.e. also in deeper layers).

In the case of wood, a basic distinction must be made between so-called wood blue stain (superficial infestation) and active mold growth due to acute moisture damage with strong mold spore formation. With normal wood stain there is usually no need for renovation. Actively infected wood, on the other hand, is very difficult to renovate and usually has to be disposed of. In exceptional cases, a superficial infestation can be removed by grinding - special protective measures must be observed.

Infested furniture with a closed surface (chairs, cupboards) must be cleaned with a damp cloth, dried and, if necessary, disinfected with 70 - 80% ethyl alcohol (Caution: Wipe alcohol over surfaces with a cloth and do not spray. There is a risk of fire and explosion ! Also use respiratory protection!). Heavily infested furnishings with upholstery (armchairs, sofas) can only rarely be cleaned with reasonable effort and should therefore normally be disposed of. Infested household textiles (carpets, curtains) can usually only be cleaned properly with great effort, so that, depending on the purchase costs, disposal is preferable.

Infested wallpaper orSilicone joints should be removed, the surface affected areas should be wiped with a damp cloth or vacuumed with a vacuum cleaner with a fine dust filter (HEPA filter) and then with 70 - 80% ethyl alcohol taking into account the risk of fire and explosion (use only small amounts, ventilate well, do not smoke, no open fire) and the requirements of occupational safety (protective gloves, face mask, protective goggles) are dealt with.

After the renovation, intensive cleaning must be carried out in the vicinity of the renovated areas. The mold-contaminated waste produced during the renovation can be packed in plastic bags and disposed of with household waste.

Protective measures for the remediation of mold infestation:

Do not touch mold with bare hands - wear protective gloves. Do not breathe mold spores - wear a face mask. Do not allow mold spores to get into eyes - dust - wear protective goggles. After finishing the renovation, shower and wash clothes.

Important: It is often recommended to use a vinegar solution to combat mold. However, this is usually not sensible, since many building materials and in particular lime neutralize the vinegar and, in addition, organic nutrients get onto the material with the vinegar, which can even promote fungal growth.

We also advise against the use of chemical fungicides (solutions with fungicides) in the interior, as it cannot be ruled out that these active substances remain in the interior for a long time and endanger the health of the residents.

The remediation of mold-infested materials must have the aim of completely removing the mold. Simply killing molds is not enough, as killed molds can also have allergic and irritating effects.

During the remediation of mold infestation on materials, very high concentrations of spores can be released. A renovation should therefore only be carried out under suitable safety and occupational health and safety conditions.

It should also be noted that a health risk cannot be ruled out for allergy sufferers or previously injured persons with chronic respiratory diseases as well as for persons with a weakened immune system, so that this group of people should not carry out any renovation work “on their own”.

More extensive renovation work should be carried out by commercial firms. For this purpose, companies are to be commissioned who are familiar with such renovation work, the dangers involved, the necessary protective measures and the regulations and recommendations to be observed.

Prevention is better than cure

The most important prerequisite for mold growth is the presence of moisture, which can mostly be attributed to structural defects and / or incorrect user behavior. Professional on-site measures and sensible room usage behavior must work together to keep an apartment free from mold growth.

The basic requirement for an apartment without mold growth is, on the one hand, the construction of the building according to the state of the art. The following serve to avoid mold growth due to moisture damage:

- minimum thermal insulation (DIN 4108-2: 2001-03),
- Protection against driving rain (DIN 4108-3),
- Sealing against rising soil moisture (DIN 18195),
- Regular roof construction (craft guidelines),
- Waterproof installations.

Particular attention must be paid to places in the outer wall, ceiling and roof area that are inadequately or incorrectly insulated or have other leaks where condensation increases.

In the case of newly built or renovated living space, significantly increased ventilation is required over a certain period of time due to the associated residual building moisture. When rooms are used with high levels of moisture and the building envelope is highly airtight, it is sometimes not possible to reduce the humidity to the necessary level by reasonable manual ventilation. In these cases mechanical ventilation can help.

Two systems in particular come into consideration for mechanical ventilation:

- Demand ventilation with exhaust fans in living areas with high levels of moisture, e.g. kitchens and sanitary rooms. The fans are expediently regulated by humidity sensors.

- Supply and exhaust air systems with heat recovery. In these systems, which are often operated in such a way that the windows remain unopened during the heating season, the air exchange should be adapted to the moisture loads that arise and the air extracted from where the sources of moisture are concentrated.

In the case of central ventilation systems, it must be ensured that these are regularly serviced and checked. Otherwise they can become a source of germs themselves. Recently, geothermal heat exchangers have also been used on the air intake side in larger systems to supply entire buildings. They can lead to a microbial problem in spring / summer when high relative humidity or even condensation occurs on the walls of the heat exchangers.

Tips for correct ventilation:


In the kitchen, a lot of moisture can be removed from the room by means of an extractor hood with exhaust air discharged into the open air. Such a deduction is also useful from the point of view of the removal of cooking vapors and - when cooking with gas - of combustion gases. Extractor hoods with air circulation are not suitable for reducing the humidity in the kitchen.


In the bathroom, the water should be removed from the walls and floor after showering. After showering, you should briefly open the window in the bathroom (if available) wide. In the case of windowless bathrooms, make sure that the built-in shaft ventilation works properly. The installation of a mechanical exhaust ventilation system - if possible controlled by humidity sensors - is recommended. Wet towels and walls in the bathroom can still contain a lot of water - despite brief ventilation; Towels are therefore best dried on the radiator and the windows open until the towels feel reasonably dry (the heating in the bathroom should not be switched off in winter, this speeds up the drying of the towels considerably; a few minutes are often enough ).

To reduce the humidity in the room, brief ventilation should be carried out several times a day (5 - 10 minutes with the window wide open).

Unheated or little heated rooms

Less heated rooms (e.g. bedrooms) should not be warmed up using warm air from other rooms (in the evening). Otherwise condensation can form on walls or window panes in colder rooms. When using the - little heated - bedroom, good ventilation should be ensured in the morning after getting up to remove moisture (every sleeper gives off water vapor). In rooms that are not used and heated for a long time, more ventilation should be provided before being used.

Correct ventilation prevents mold

The behavior of the apartment users can also help prevent mold from finding favorable growth conditions in the apartment: Correct ventilation and heating can limit the humidity in the building.

It is important that the moisture generated by activities in the room (loss of moisture from people, showering, cooking, washing, etc.) is removed to the outside through regular ventilation.

The possibility of removing moisture from the room by ventilation is based on the fact that air can absorb different amounts of water vapor depending on the temperature. With the same relative humidity, warm air contains much more water than cold air. Cold outside air in winter contains little water, even if its relative humidity is high.

Cold outside air that gets into the interior when it is ventilated absorbs moisture when it is heated, which is then discharged to the outside with the heated air. If the outside air is very cold, ventilation can be used in the interior - even in rainy weather. The colder the air, the more water it can absorb when heated. Therefore, ventilation with cold outside air can remove more moisture from a room in winter than in summer.

In a three-person household, around 6 to 14 kg of water are released daily through the release of water vapor by people (30 to 100 g / h per person) through showering, washing, drying clothes, cooking and through plants, aquariums and other sources of moisture. Several cubic meters of air have to be moved in order to remove 10 kg of water from indoor spaces. This means that the air in the interior has to be changed about 7 times a day on average in order to remove the unwanted moisture. For comparison: with closed windows and doors, air exchange rates between approx. 0.2 - 2 per hour (depending on the window type and construction situation), with wide open windows the air exchange rate increases to 10 - 20 per hour.

The poorer the thermal insulation of the external walls or the more structural mistakes have been made in the building construction (for example in the form of thermal bridges) and the worse external walls are heated by circulating room air (for example behind cupboards or behind wall cladding), the lower it is in winter the surface temperature of these outer walls. This increases the relative humidity on the inner wall surface and the risk of condensation forming accordingly.

In basement rooms in old buildings, the wall temperature on the side of the room is often low, even in summer. However, since the absolute humidity of the outside air is often high in summer, frequent ventilation with outside air to "dry off" would be wrong, because more and more humidity is brought into the room and condenses on the cold walls. Ventilation should then be postponed until the early hours of the morning.

In basement rooms that are only used as storage and are not intended for long-term use by people, mold infestation is sometimes accepted. The only remedy would be better thermal insulation, heating or drying the room air. Basements, in which mold growth cannot be prevented, should not have a direct connection to the rest of the building, for example through stairs, shafts or unsealed openings in the basement ceiling.

Important: On outside walls, especially with "cold" walls, no pieces of furniture, pictures or heavy curtains should be placed directly on the wall or hung on it. A minimum distance of approx. 10 cm can be used as a guideline.


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Source: Advisor 'Mold in the House' from the Federal Environment Agency