Black mold on windows

Because of condensation, windows are the main place of black mold in the house. If black mold has already appeared on your windows, then do not hesitate - it is necessary to declare a war against it and destroy it completely.

We tell you why mold appears, how to remove it with household chemicals and to prevent its reappearance.

The old wooden frames have been replaced with plastic ones. In addition to the long-awaited silence and absence of droughts, the happy owners of the new systems faced a new problem. On the soffits, frames and window sills, unpleasant black stains appeared, and it is not easy to remove them. Let’s find out where black mold on plastic windows comes from and how to get rid of it for good.

Why mold stains appear

To successfully cope with the unpleasant phenomenon, you need to know what it is. Black mold is a fungus with an unusual structure. Under a microscope, it looks like a thin thread, united with balls. These are the spores with which the organism reproduces, according to (1). It grows on top, that is, it is constantly stretching upward, scattering matured spores.

The biggest difficulty is that mold fungi never live singly, only in groups. They are called colonies. Each of them seeks to capture as much living space as possible, that is, to expand over as large an area as possible. They are especially good at this in a humid and warm environment. Wet and warm environments stimulate rapid colony growth.

Black mold is a very unpleasant neighbor. Sometimes it is believed that its appearance is only an aesthetic problem. In fact, everything is much more serious. Fungal spores are a strong allergen, provoking the appearance and further development of asthma, bronchitis, various manifestations of allergies, increasing the risk of cancer, states R.Mammadli. That is why you need to get rid of mold immediately. Especially while the colony is small, it is the easiest thing to do.

Mold fungus appears where high humidity and temperature above 60F are combined. These are the best conditions for its development.

Causes of occurrence:

  • Installation of the window system carried out with errors, as a result of which the double-glazed windows are depressurized.
  • Absence or inefficient operation of ventilation. Especially if the window sill and soffits are wide.
  • Heavy, dense curtains were chosen that do not let air in to the glass.
  • Lack of ventilation, which disturbs the natural air exchange.
  • Seasonal change in the microclimate of the room, associated with the active operation of heating and irregular ventilation.

Systems made of plastic are airtight, micro-ventilation, as was the case with wooden ones, is impossible with them. Therefore, all the reasons described above inevitably lead to condensation. It accumulates in the corners of frames, spreads along the window sill, rises along the window sill. If you do not take any measures, the next stage will be mold fungus.

How to remove black mold on windows

A variety of means are used to destroy mold colonies.

Information provided by

Chemical products

  • Fungicides. Chemical solutions that destroy microorganisms. They can be fast and prolonged action. The latter option involves the protection of the surface for up to five years.
  • Chlorine lime. An aqueous solution of this substance prevents the growth of the colony, quickly destroys it.
  • Sodium perchlorate. It is used in the form of a solution. It cannot be applied to porous bases, such as plasterboard. It destroys the structure of the material.
  • Grapefruit or tea tree oil. A powerful antiseptic. Diluted with water in the ratio of 1 tablespoon of the product for a glass of clean water. It is sprayed on the affected area. The composition is also used as a prophylactic. It is sprayed, left for a long time.

It is possible to get rid of mold microorganisms with the help of folk remedies. These are vinegar, hydrogen peroxide, copper sulfate, boric or citric acid, alcohol. They are used singly or combined in different proportions. For example, users recommend the following recipe: 100 ml of bleach and 0.4 oz of copper sulfate are diluted in a liter of water. The resulting preparation is used to treat problem areas.

A good result depends not only on what to treat mold on the window sill of plastic windows, but also how to do it. In addition to chemical means, and better in combination with them, other methods are used.


  • Mechanical cleaning. The stain is scraped off with any sharp object. Anything that is scraped off should be removed immediately.
  • Quartzing. A quartz lamp is directed to the infected area, turned on for half an hour. People and animals leave the room for the treatment period. At the end of the session, the dead colony is mechanically removed from the surface.
  • Heat treatment. The mold microorganisms are destroyed by a directed stream of heated dry air. Take a household or construction hair dryer for this purpose.

Ultraviolet irradiation helps well. But you should only use a professional radiator.

How to fight black mold

  • We take a rag, moisten it with water and scrub the stains. If the mold infestation is extensive or it is “embedded” in the base, scrape it with a sharp object.
  • Prepare a working solution of the chemical preparation, following the instructions exactly. Apply it to the surface. Leave it for the specified period of time.
  • Rinse the surface with clean water and remove the solution completely.
  • Thoroughly dry the problem area. To do this, first wipe it with a dry rag, then use a hair dryer to direct a stream of hot air at it.

This is how to remove mold from window sills or windows. In conclusion, you can additionally spray an aqueous solution of grapefruit or tea tree oil on the cleaned area. It is not necessary to wash it off. The rags used for cleaning should be thrown away or disinfected properly.

How to remove black mold on the slopes of plastic windows

If the problem area is found on the slope, it is much more difficult to cope with it. The technology depends on what material it is made of. If the finish is plastic, proceed as follows:

  • Disassemble the slope. Very carefully remove the elements so they do not break.
  • Clean the elements as described above.
  • Carefully examine the plane of the window slope. All detected areas of voids are filled with foam. Wait until it dries, cut off the excess.
  • If the surface formed a mold colony, remove it. Treat the area with fungicide or any other suitable composition.
  • We dry the base, use a hair dryer for this purpose.
  • Put all the elements back in place.

If the slope is made of plasterboard and black spots of mold appeared on it, it is unlikely to save the detail. GPB is a porous material, in addition, even moisture-resistant sheets do not withstand intensive washing. All this makes a complete treatment impossible. Therefore, the affected parts are dismantled and replaced with new ones. Before installing them, the place where they will stand must be disinfected.

How to get rid of excess moisture

The main reason why black mold growth appears on the window system is high humidity. It must be normalized, otherwise there is no point in fighting the fungal infestation. Efficient ventilation will help. Where there is no ventilation, you will have to install a new system. And if you have it, but it does not cope, you will need to reconstruct and possibly install additional equipment. Will help, for example, the conditioner of sufficient capacity.

It is better to choose a device with a filter with additional fungicidal impregnation. It will effectively get rid of dangerous fungal spores. Sometimes the problem lies in too wide a window sill. Warm air simply does not reach the glass, where condensation forms. A good solution is to install blinds made of plastic. A hole is made in the window sill, which is closed with a plastic grid with blinds. They will direct the hot stream from the batteries to the glass pane.

Effective means to control humidity – ventilation valves that are built into the window frames. This is done at the installation stage or in the course of operation. With increasing moisture content in the air, they automatically open, with decreasing moisture content they close. This provides a constant air flow and normalization of the microclimate. There is no draught, because the size of the element is small.

Mildew is a dangerous neighbor in the apartment. Its presence threatens health, so it is necessary to get rid of such a neighborhood as soon as possible. There are no special difficulties here. It is easy enough to destroy microorganisms at an early stage of colony development. It is more difficult to remove overgrown stains that have penetrated deep into the building materials. But even with this you can cope, using several effective means in combination.


I enjoy acquiring knowledge and sharing it. I am a long-time health advisor and blogger for over 12 years. Understanding the dangers of black mold to people, I felt it necessary to share with readers the basics of fighting and preventing black mold in homes and other living spaces.

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