Mold growth on concrete can not only look unsightly but over time can cause damage, and in extreme circumstances, has the potential to be hazardous to both humans and animals.
In this article, we will be exploring the main causes of mold growth on concrete, the types of mold that are typically found, how to identify the type of mold you are dealing with, and how to effectively remove and prevent its return.
The most effective way to kill mold on concrete is to use distilled white vinegar. Apply diluted white vinegar to the affected area and leave for ten minutes to kill the mold at its roots. To remove, use warm water, detergent, and a soft-bristled brush to scrub the mold away.
Can mold grow on concrete?
Mold certainly can grow on concrete, in fact, mold can grow on many surfaces as long as the conditions are correct. As long as mold and mildew have a source of moisture, nutrients, an ambient temperature between 60-80 degrees Fahrenheit, and a lack of natural sunlight, it can thrive.
Moisture in outside spaces can come from poor drainage and high humidity (such as after frequent rainfall) and nutrients are easily obtained, as any source of rotting organic material can be used by mold as a source of food.
You will most often find mold growing on concrete where there is a lack of natural sunlight, the reason for this is that the sun’s UV rays will kill both mold and its spores on contact so it will usually grow in cooler, shaded areas.
What causes mold on concrete?
As stated above, mold only needs moisture, nutrients an ambient temperature between 60-80 degrees Fahrenheit, and a lack of natural sunlight in order to survive, however, there are several common causes that increase the likelihood of mold growth on concrete.
Within a property, flooding is a frequent cause of mold growth on concrete walls, ceilings, and floors. Despite its appearance, concrete is a porous material, therefore, after a flood has occurred, water can be retained for a considerable time within the concrete itself. If a room (such as a basement), is not fully dried as quickly as possible after flooding, mold growth can occur.
Modern homes are becoming more and more insulated. Whilst this is a good thing for heat retention and energy saving, it does not let properties “breathe”, as there is a lack of airflow through the home.
As concrete walls usually have a lower temperature than partition walls, moisture retained within the home will often begin to condensate on the cooler surfaces it finds, this being the concrete walls.
Frequent high moisture levels, nutrients from dust within the home, and consistently warm temperatures are a recipe for mold growth.
Lack of ventilation
As previously stated, modern homes are being insulated to the point where they are becoming near airtight. And whilst this keeps heat in, it also keeps fresh air out. A constant flow of fresh air is what gives mold spores a hard time settling down on one surface and starting a colony, without airflow, mold can easily settle and begin establishing itself.
Lack of natural sunlight
Mold is a fungus, and as such does not require natural sunlight in order to grow. In fact, the sun’s UV rays will kill both mold and its spores on contact, so mold tends to flourish in areas that lack natural sunlight, or at least get less of it. This is often why you will find mold growing in darker areas of your home, such as a basement.
What types of mold grow on concrete?
The most common types of mold you may find growing on internal or external concrete walls are:
- Stachybotrys Chartarum (black mold)
- Aspergillus Niger
Although this list includes the most common strains typically found growing on damp concrete structures, the list is not exhaustive, there are thousands of strains of mold that have the potential to be able to reproduce and live happily on a concrete surface, these are simply the most commonly seen.
Can mold growth damage the concrete?
Yes, mold secretes digestive chemicals that break down organic materials which it then consumes. Over time, these chemicals can begin to degrade concrete and weaken the integrity of the material.
Of course, in order for significant damage to be caused to concrete surfaces by mold growth alone, a considerable amount of mold must be present for some time before any noticeable damage is incurred.
Is it definitely mold?
Before you assume that what you are dealing with is definitively mold on concrete, it is important to rule out other options.
What May look like white mold growing on a concrete surface could in fact be something called Efflorescence.
Efflorescence is caused by the hydrostatic pressure of liquids passing through concrete and forcing out naturally occurring mineral salts. These salts can resemble white candy floss and are often mistaken for a form of mold.
To test whether you are dealing with white mold or efflorescence, pour a small amount of water on the substance. If it is efflorescence, the minerals will dissolve, if it is white mold, it will not.
What does mold on concrete look like?
The most commonly found molds previously listed come in a variety of shades and textures. The following will explain what each type of mold looks likes whilst growing on concrete so that you can try to identify the particular strain growing.
Stachybotrys Chartarum (black mold)
Stachybotrys Chartarum is commonly known as black mold and can be seen as small patches of a circular greenish-black color, with some small patches of grey.
These patches can often be seen clumped together to form larger patches, with very small singular circles also seen. These patches often have a slimy texture and appear shiny when moist.
Aspergillus niger looks very similar to black mold, in that it forms in small circular dots that clump together to form larger patches.
Often forming in black, grey, and sometimes dark brown colors, it has a consistency of cotton.
Alternaria strains form in small circular patches that often clump together to form larger masses, and can appear grey to black with dark olive-brown flecks. And often has a woolly or velvety texture.
Cladosporium has dark colorations that include brown, grey-green, and blackish-brown. Often appearing in clusters with a powdery texture.
Chaetomium begins as small patches of white growth with a fuzzy texture that becomes darker, turning to a dark blue-olive green coloration. It is best described as having a cotton-to-velvet texture.
Ulocladium again appears in darker color tones, including dark brown to greenish-black, with a texture that is often compared to that of suede.
Is mold growth on concrete dangerous?
Yes, mold growing on a concrete surface such as a wall either externally or internally can be hazardous to the health of both humans and animals.
Certain strains of mold produce metabolites called mycotoxins as a defense mechanism whenever they feel threatened, by being disturbed for example.
For mold exposure to cause noticeable health complaints usually requires either large areas of mold or being exposed for a prolonged period, however, for people who are sensitive to mold, or who have a compromised immune system, even small amounts of mold exposure can cause serious health conditions.
Some of the most commonly seen symptoms of mold exposure are:
- Brain fog
- Muscle aches
- Skin irritation
For people with allergies or sensitivities to mold, allergic asthma attacks, liver damage, and even some cancers have been reported.
How to remove mold on concrete
As previously mentioned, mold can be hazardous to humans and animals, therefore, when attempting to remove it yourself, you should wear the following safety equipment.
- Breathing mask – To avoid inhaling spores or chemicals
- Rubber gloves – To avoid contact with the mold or any chemical cleaners
- Eye protection – To prevent any chemicals or mold spores from coming into contact with the eyes
The following are the most effective ways of removing mold from concrete surfaces.
White (distilled) vinegar is an effective way to both kill and prevent mold growth on concrete, however, its acidity levels are high enough to cause damage if saturated and left for prolonged periods, especially on unfinished concrete surfaces.
To effectively clean mold from concrete using vinegar, use the following steps.
Step 1. Prepare a vinegar solution
For newly formed mold patches, make a solution from one cup of white distilled vinegar to one gallon of water.
For established mold, you can use undiluted vinegar instead.
Step 2. Apply the solution
For large areas of mold growth, dip a sponge into the solution, wring it out slightly so that the sponge is not saturated, and wipe over the affected area.
Step 3. Allow time for the vinegar to work
Leave the vinegar solution on the affected area for at least ten minutes to give it enough time to kill the mold at its roots.
On unfinished concrete, vinegar can begin to cause damage if left for too long, so ensure that it is left for a maximum of 15 minutes before removal.
Step 4. Scrub
With a solution of warm water and detergent, use a soft-bristled brush to work the vinegar solution into the mold using circular motions. As the vinegar has had time to kill the mold, the detergent should be able to easily lift it and its roots from the surface.
Wipe over with a clean towel or cloth to remove any mold or detergent residue.
Step 5. Dry
As previously stated, mold loves moisture, so once you have cleaned the affected area, use a dry cloth to wipe the cleaned area down to remove as much moisture as possible.
If cleaning a concrete wall within a property, consider using a dehumidifier in the room to remove any access moisture along with wiping the walls down.
Bleach is a powerful cleaning agent, and so has the ability to kill and remove mold from most surfaces.
It can stain surfaces though, so take precautions when working indoors to prevent staining of carpets, etc by putting down protective sheets and reducing runoff from brushes, etc.
To clean mold off concrete surfaces with bleach, use the following steps.
Step 1. Dilute and apply the bleach
In a large bucket, add one cup of household bleach to a gallon of water.
For indoor surfaces, (whilst wearing protective gloves) use a sponge to apply the bleach solution to the affected area. Be careful not to overly saturate the wall as concrete is porous and will absorb excess liquid.
Step 2. Scrub
Leave the bleach solution on the affected area for at least ten minutes, this will give the chemicals within it time to work into the roots of the mold, killing it permanently.
After ten minutes, dip a soft-bristled brush in the bleach solution and scrub. As the mold should be already dead, it will easily come away from the concrete surface.
Step 3. Wipe and dry
As you want to keep the moisture levels as low as possible, use a damp cloth to wipe or dab away the bleach and mold residue.
Once all the residue has been removed, use a dry cloth to absorb as much of the water as possible. Remember to wear rubber gloves when working with bleach.
Using household detergent can be an effective way of removing mold from concrete. If you are cleaning unfinished concrete, detergent may not be strong enough to kill the mold, however, on smooth, finished surfaces, the detergent will still remove the mold.
In order to remove mold effectively from concrete using detergent, use the following steps.
Step 1. Make a detergent solution and scrub
Mix one cup of detergent with a gallon of warm water. Dip a soft-bristled brush in the detergent solution and scrub the area until the surface mold has been removed.
Step 2. Wipe and dry
Using a dry cloth or sponge, remove the detergent solution and mold residue, then with a dry cloth or sponge, wipe or dab the area to remove as much of the visible moisture as possible.
Mold removal products
There are many specific mold removal products available that can be used to effectively kill and remove mold found growing on the surface of concrete.
Popular options available on Amazon.com include:
RMR-86 Pro Contractor Grade Mold Stain & Mildew Stain Remover
For UK homes, the following products are available on amazon.co.uk
These products have been shown to effectively remove mold from surfaces such as paving slabs, fences, and concrete.
In order to use them most effectively, follow the recommended usage guides that come with the product.
For outside concrete surfaces, a pressure washer will be very effective at removing mold and mildew from concrete surfaces.
To make the pressure washer even more effective, you can add detergent, just make sure it is compatible with the brand of pressure washer you are using.
To use a pressure washer to remove mold, use the following steps:
Step 1. Add detergent to your pressure washer
Step 2. Spray the surface with the detergent solution and leave for ten minutes
Step 3. Using only water, and on a high-pressure setting, spray the affected area until all traces of mold have been removed.
How to prevent mold growth on concrete
Prevention is the best cure, so making sure that you are not affected by mold growing on concrete before it occurs is always preferable to having to deal with the consequences after it has begun. You can also use the following tips to make sure that if you have already had to deal with this irritating issue, it does not occur again.
To prevent mold from growing on concrete, use these preventative measures:
Seal the concrete surface
Concrete is a porous material, therefore water can seep into the material. Over time, if large enough quantities of moisture remain within the concrete, damage can be caused, and mold will also begin to grow. By using a sealing product, you create a waterproof barrier that will increase the lifespan of the concrete and prevent mold from being able to grow.
Recommended concrete sealers include
Raincheck universal water seal
Eco Advance concrete/masonry siloxane waterproofer
When to call a professional
As we stated earlier in the article, mold growing on concrete can be hazardous to the health of humans and animals. Therefore it can be potentially dangerous to clean the mold yourself if you do not have the correct safety equipment.
There are also points where mold infestation may have become too well-established for home removal. In this case, it may be worth hiring professionals that have the correct equipment and chemicals to deal with hard-to-remove mold and mildew.
If you are unsure of any aspect of removing mold from concrete yourself safely, it is advised that you book a professional inspection.
Mold on concrete surfaces can be tricky to remove, but it is possible. Detergent solutions work best on smooth, finished concrete, whereas vinegar and bleach solutions are more effective on rough unfinished concrete surfaces.
Mold left on concrete can damage and weaken the integrity of the material if left untreated, so as soon as it is discovered, it should be removed either by yourself or a professional.
Can toxic mold grow on concrete?
Toxic mold can indeed grow on concrete surfaces. Stachybotrys chartarum (Commonly called black mold), is often seen growing on concrete walls and surfaces and has the ability to produce toxic mycotoxins which can cause allergic reactions and other serious health complaints.
How fast does mold grow on concrete?
Mold can grow incredibly quickly on concrete if the conditions it needs are adequately met. As long as there is moisture, a source of nutrients, and a lack of sunlight, mold can begin to grow within 24-48 hours. If untreated, mold can become deeply established within two to three weeks.
Can you paint over mold on concrete?
Painting over mold is never a good option, as if the underlying cause of mold growth is not addressed, it will continue to expand and become more deeply rooted. Only once the mold has been completely killed and removed should the surface be painted.