Is Concrete Prone To Mold Growth?
Mold can easily grow on food, paper, wood, rug, and fabric. But can it thrive on concrete, too?
The problem with concrete is that it’s usually the building material we use for basements, patios, steps, garages, etc. These places are generally cold, humid, and therefore more likely to have a mold problem.
This increases the concerns about whether mold fungus can spoil our concrete walls and cause related problems such as respiratory problems, skin conditions, and structural damage.
So can mold grow on concrete? How fungi affect concrete walls? And how can we prevent mold growth on concrete?
We will answer all these questions below.
TLDR; (Too Long, Didn’t Read!)
Yes, mold can grow on concrete. Although concrete is not organic and does not provide food for mold, the dust and debris that accumulate on a concrete slab provide all the nutrients that mold fungus needs to survive. The only way to prevent that is by limiting the moisture supply to concrete by waterproofing, proper ventilation, and dehumidification.
Can Mold Grow On Concrete?
The quick and confident answer is YES. Mold can grow on concrete.
Like any other creature, mold needs oxygen, water and food to survive. What do they feed on? They feed on organic and carbon-based materials.
This includes paper, wood, fabrics, carpets, hair skin, food, etc.
Ok, but concrete is not organic. How does it provide food for mold?
Whilst concrete is not organic and therefore does not provide food for mold. However, keep in mind that many organic substances can be found on a concrete surface offering enough nutritional supply for fungus to grow and spread.
Tiny residues like dust, salts, debris, dead skin cells, hair etc. can all settle on a concrete slab making it a suitable land for mold buildup.
So unless you can keep your concrete extremely and permanently clean, mold will always find a way to grow upon it.
What’s more? When mold spores spread and feed on organic materials, they release some acids and digestion enzymes that degrade the infected surface and reduce its integrity.
For concrete, this makes it weaker, less dense, and more porous. As a result, it becomes prone to further moisture, dust, debris, and mold intrusion.
Another thing that supports mold growth on concrete is putting sheetrock, or drywall, directly on concrete.
Mold can easily grow on drywall because it’s highly organic. Therefore, when you put a drywall board against a concrete wall, mold can easily travel to concrete and rapidly spread over a wide area.
This is also the case when there is wood flooring, window framing, carpets, or rugs near concrete. These matters are highly organic and therefore can grow mold and emit some fungus to concrete where they can continue multiplying.
The infection can also be in the opposite direction.
How To Tell If You Have Mold On Concrete?
Spotting mold on concrete can be a challenging task.
The dark grey color of concrete makes it quite difficult to identify mold stains and you can end up accusing other things, or worse yet, neglecting hidden mold colonies that can harm both your concrete slab and your health.
In general, black mold should not be difficult to spot, but when it’s white mold growth, that’s when things get tricky.
If you find white (or light-colored) stains on concrete, it can be just efflorescence and not necessarily mold.
What does efflorescence mean?
Efflorescence is a powder-like substance that you may find on the surface of some construction materials like concrete, cement, brick, or masonry.
Efflorescence forms when moisture moves through such materials and carries with it all the minerals and salts within.
Now when this moisture shows up on the surface, it evaporates and leaves behind all the carried minerals, which in turn form a white (or yellowish) crystalline-like structure.
How can we differentiate mold and efflorescence?
First, mold grows in size over time while efflorescence doesn’t.
Second, efflorescence feels hard to the touch and if you grab it with your hands, it turns into powder easily. In contrast, you cannot change the structure of mold.
Also, spraying water on efflorescence makes all the minerals dissolve and disappear. Conversely, water does nothing to mold and cannot remove it.
Another way to identify mold is through smell.
In general, mold has a musty or earthy smell. Some also describe mold to smell like a damp fabric, sweaty socks, or rotten food.
The last thing worth noting here is that a moisture meter can help to identify mold on concrete, especially if that’s supported by clear visual indicators.
This will depend on which moisture meter or more specifically, which reading scale you use.
If your moisture meter is calibrated for concrete and has a dedicated reading scale for it, then you should expect values less than 2%.
Concrete has a tight structure and therefore should not hold a lot of moisture.
In other words, concrete is meant to be bone dry and damp-free. So even extremely low readings can suggest saturation and too much dampness.
Now if your moisture meter is not calibrated for concrete — which is probably the case because most moisture meters are calibrated for wood — then you should switch the instrument to the reference scale and compare the values you get to a dry concrete sample.
Let’s explain further.
A reference scale is an additional reading scale that you can find on most moisture meters. The reference scale allows you to test humidity in materials for which the instrument has no reading
For example, a wood moisture meter has a reading scale for wood, but it can also have a reference scale that allows testing moisture on drywall, concrete, tile, bricks, etc.
Now be careful here. The values you get on a reference scale are just qualitative estimates. Meaning, they are not the actual moisture content of the material under test, but only how much water is in there compared to a dry reference.
This is why, if you are to use a reference scale on concrete, start first by taking the reading of a sample slab that you know for sure is dry and mold-free.
Save the reading you get somewhere and use it as a baseline or reference for your future checks.
If other slabs give the same values, then it’s safe to consider them as dry and less likely to have mold. If instead, you find higher readings… you know the answer.
How Does Mold Affect Concrete?
As we previously said, when mold spreads over a concrete slab and feeds on its organic content, it releases a few acids and enzymes that hurt the integrity of concrete and make it more porous.
This allows more dust, moisture, debris, and mold to penetrate the slabs and cause further damage.
Now, as mold grows its territory on a concrete wall, more fungi go airborne, increasing the risk of respiratory infections, breathlessness, allergies, eczema, skin irritations, etc.
And of course, no need to mention the foul smell of mold, especially in closed areas, and the unpleasant look of mildew stains on a wall.
How to prevent mold from growing on concrete?
Moisture reduction is the only thing you can do to prevent mold growth on concrete.
You can try to wipe your concrete walls and remove any dust or debris that can provide food for mold. But is it something you can do every day? Do you find a lot of fun in chasing dust residues on your walls? And will you be able to clean every inch of every concrete surface in your
Yes, periodically cleaning your walls and floors is beneficial and will help reduce mold problems, but let’s face it, it’s not something you can do every day and, dust and debris will always manage to settle on your walls and thus initiate mold.
Therefore, the only thing that you can really control here is moisture.
Mold needs water to thrive, so if you can reduce the water supply to your concrete slabs, you can drastically limit mold growth and development.
In addition, moisture control will also improve your comfort and wellbeing, reduce the risk of many health problems, and prevent mold growth in all the items and surfaces in your house, not only concrete.
In other words, reducing the humidity level will give you big leverage in your battle against mold, much bigger than just cleaning concrete and removing dust.
Ok fine. Now how can I reduce mold-inducing moisture?
What you should know here is that damp can access your concrete via 3 main sources.
Condensation happens when hot, humid air hits a cooler surface.
When this happens, the water holding capacity of the air decreases and all the excess vapor turns into a liquid state and forms water droplets on that surface, causing moisture intrusion and mold growth.
Now when it comes to concrete, the risk of condensation is generally higher. Why? Because concrete is a poor insulator. As a result, when it’s chilly outside, your interior concrete will also be cold and in consequence cause more condensation.
So how can we prevent that?
Well, the first thing to do is to improve ventilation in your building.
The goal is simple. You want to ensure good air circulation through your house so that damp air goes outside before it hits your concrete walls and condenses.
Also, you want to let dry outdoor air come in so the indoor humidity decreases to a safe level.
Many things can help with that:
• Cracking windows and doors open.
• Installing vent fans all over the house.
• Investing in a ventilation system.
• Installing an AC that dries outdoor air before pumping it inside.
If you can’t have these in every area of the house, then focus on the rooms most susceptible to have a condensation problem.
The kitchen, bathroom, laundry room, gym, crawling space, basement, garage, etc. are all places where damp air circulates and therefore poses a condensation risk.
So make sure to ensure proper ventilation in such rooms.
In addition, it’s highly recommended to have a cooking hood and extractor fan in your kitchen and bathroom. These simple items are effective at redirecting damp air out before they touch the walls.
Also, when bathing or cooking, make sure to close all the doors that connect the kitchen/shower to the other rooms of the house.
You want to keep problematic air in a tight and controllable area.
Moreover, avoid putting wet and damp items in closed areas, and always hang your clothes to dry outdoors, or at least in a dryer that vents outside.
All these are simple DIY moisture prevention measures that you can take to prevent mold growth in concrete.
However and unfortunately, condensation is not the only cause of mold. Rising and penetrating damp can also cause fungus to infect concrete and therefore deserve our prevention efforts too.
Rising and penetrating damp
Flooding can easily occur in a basement.
As many homes do not have a water barrier separating the foundation and earth, water from rain or watering the lawn can effortlessly funnel to the basement and cause flooding.
This can also happen if the building foundation is under or near the water table.
Now as this water sits and accumulates under a house, moisture starts seeping up through concrete slabs in the basement, making them damp and therefore more susceptible to develop mold.
Worth noting here that concrete doesn’t need to have large cracks or pores in order to let moisture penetrate.
When water accumulates in the ground of a building, this creates a powerful hydrostatic pressure able to push water through the porous nature of concrete.
Water can also penetrate exterior concrete through rain, snow, or simply if the outdoor humidity level is high.
Walls cracks and holes make this risk higher because they trap more water inside the walls and prevent it from drying, which promotes fungal and mold development.
Now how can we stop rising and penetrating damp from getting into concrete?
Well, the most important thing here is to install a drainage system in your basement.
The goal is to drain water away from your house’s perimeter and send it to a far place where it is no longer problematic.
A sump pump, French drain, or waterguard are the most common solutions for this.
You can decide which one to use yourself, but asking a specialist is always the best way to go.
These guys know which drainage system is suitable for each flooding situation and will help you pick the right direction.
Also, remember to check your gutters and downspouts and make sure they are redirecting water away from your walls and foundation.
Extending them to push water even further can also be worth the investment.
Another thing that you can do to prevent mold growth on concrete is to apply a penetrating primer on it.
This will make moisture and rainwater less likely to penetrate the concrete slabs and therefore less likely to initiate mildew growth in them.
Another option would be to cover concrete with another material like tile, paper rocksheet, or drywall. However be careful here. Only put another layer on concrete if it’s mold-free and sealed.
Drywall is highly organic and can grow mold easily. As a result, putting it on unsealed concrete will make it easy for fungus to travel between the two materials and cause irreparable damage.
So first apply a primer to concrete, then cover it with whichever material you want.
Summaries On Concrete Mold Growth
Yes, mold can grow on concrete. Although concrete is not organic and provides no nutrients for mold, it can accumulate other tiny substances that do.
Dust, debris, hair dead skin cells, can all be found on a concrete slab providing molds with all the food they need to thrive.
Also, organic materials such as drywall, rocksheet, carpets, or wood, if placed near concrete surfaces can easily transmit mold spores to them and initiate the fungal growth.
Now in order to keep your concrete mold-free, you can either spend hours trying to make it extremely clean, which is, practically, not doable, or you can put efforts into reducing moisture, preventing basement flooding, and keeping indoor air dry.
As always, we hope you found this article helpful, but if you need a professional touch then call the number on this page for support.
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J. Sullivan – New Orleans