Why does my concrete patio sweat and is it dangerous?

If you’ve woken up after a particularly humid night and found the floor of your concrete patio floor sweating, it is a phenomenon that we call concrete sweating. Fear not, this is not a leak, but more because warm humid air came into contact with the cool concrete floor. In this short read, we’ll tell you what concrete sweating is, if it’s dangerous and ways to reduce or control the phenomenon.

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What is concrete sweating? Why does my concrete patio sweat?

Sweating slab syndrome, or concrete sweating, as it is popularly called, is a phenomenon characterized by moisture forming intermittently on the surface of an interior concrete slab, such as a patio or garage flooring. 

In layman’s terms, when warm moist air comes into contact with the concrete slab, the colder concrete floor temperature causes condensation to build up on the surface. The moisture that builds up, as a result, is what we call sweating. The condition is commonly found when warm air flows into a building that has relatively colder flooring.

Is concrete sweating dangerous?

Here are some of the reasons why concrete sweating can be a dangerous situation.

Mold

If you leave a concrete floor unchecked for a long time, one of the major problems you can expect is the growth of mold and mildew. Mold is one of the largest spreaders of pulmonary diseases and airborne allergies.

Concrete cancer

Also known as an alkali-silica reaction, this is a swelling on the surface of the concrete that happens as a result of the reaction between concrete, which is highly alkaline, and non-crystalline, amorphous silica in the presence of moisture. 

ASR can lead to non-repairable issues with concrete, including cracks in the concrete, which may lead to permanent structural damage. 

One of the main reasons this happens is because a vapor barrier may not have been installed under the slab when the concrete was poured. This allows moisture from the ground to seep up as well, making the condition worse.

Slippery when wet

Irrespective of whether your concrete floor is at home or in a commercial establishment, wet concrete is a slipping accident waiting to happen. The growth of mold on wet, sealed concrete makes it an even more dangerous surface to tread on.

Can we stop concrete sweating?

We now know what causes the concrete to sweat and the dangers the phenomenon can give rise to. Let’s take a look at what measures we can take to prevent this from happening and to control it if it persists.

Ventilation

Moisture levels are higher in areas that see a lot more water, such as bathroom floors, showers, laundry rooms, etc. Keeping these places well ventilated is a great way to ensure moisture has a way to exit the room and does not settle on the surface of the slab.

Vapor barriers

Making sure vapor retarders or barriers are installed in between the native soil and the concrete floor is an efficient way of ensuring moisture cannot seep in through the floor and preventing sweating slab syndrome.

Insulation

Whether you are looking at slab-on-grade foundations or below-grade basement walls, concrete sweating can be prevented if we make sure we install adequate thermal insulation between the native soil and the concrete. This helps regulate temperatures between the external atmosphere and the room temperature.

Good housekeeping

Certain housekeeping and maintenance practices can also help control moisture build-up on concrete floors.

It is advisable to use a penetrating concrete sealer on the concrete to keep the moisture out. In fact, it may be better to first use a concrete densifier primer and then a penetrating stain repellant.

It also helps to use a strong cleaning agent and scrub the floor regularly to remove excess debris and slab moisture.

HVLS fan

Using a high volume low speed fan works well to clear the room of excess moisture, especially in commercial settings.

Dehumidifier

Alternatively, a dehumidifier is also an effective way of controlling the amount of moisture vapor the room has and controlling concrete sweating.

Air conditioner

Finally, either turn up the heat or turn down the air conditioning in the room to match the temperature of the air in it with the floor temperature. That way, condensation can be avoided.

Read more: How to remove paint from concrete

Written by Narayan Shrouthy. February 17, 2022

Narayan is a content writer for Kukun. With experience in both content writing and editing, Narayan mixes his writing and love for reading with his passion for music. As an active musician, He aims to be a key player in Kukun's content experience.

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grace_b10@yahoo.com(@grace_b10yahoo-com)

oh my god, I thought it was a miracle issue, not a condensation issue ha ha