Why is My Concrete Floor Sweating Under the Carpet?

On concrete floors, the common reason for “sweating” under the carpet is condensation, especially in warm weather. When warm air comes into contact with the cold concrete, it condenses, causing wetness.

Sometimes you will not notice it if you have your room well-ventilated because it evaporates. However, in areas covered by the carpet, the moisture (the sweating) will not evaporate for obvious reasons.

Why is My Concrete Floor Sweating Under the Carpet?

It is not exposed; thus, it can’t evaporate, and that’s why you find your concrete flooring sweating under the carpet. After some time, you can notice that the area underneath it starts to darken.

This sweating is also called the sweating slab syndrome (SSS).

Another cause of this wetness under the carpet could be the lack of a moisture barrier beneath the slab, hence moisture rises to the surface of the floor through a process known as rising damp.

Effects of Sweating on the Concrete Floor

When not dealt with, this sweating could be a hazard not only on the floor itself but also to you.

It creates a slippery surface which is a high risk within your living space. Especially if you have kids. They are always running around, it’s so easy for them to trip.

Sweating on concrete flooring causes a problem commonly known by experts as Pandora’s “MAD” box.

It stands for:

  • M=Mold growth
  • A=Alkali Attack
  • D=Dangerous Slick conditions

Let me give you a deeper understanding of what the above problem means.

Mold Growth

First things first. Mold is a health hazard. It is a predominant factor in airborne allergies and pulmonary problems. Moisture if let to sit for long will start to attract mold.

Mold Growth

Because the carpet is very heavy, the moisture does not evaporate easily if you rarely take your carpet out to dry. The mold spores will start to form and multiply fast with time.

Alkali Attack

Alkali attack also known as concrete cancer is a reaction that occurs in the concrete between the highly alkaline cement paste and non-crystalline silicon dioxide, found in many common aggregates.  

Alkali Attack

The Alkali Silicon Reaction (ASR) as the experts call it. ASR causes serious cracking in concrete; which causes structural problems.

If you have seen a white residue that almost looks like foam on concrete, it’s the alkali attack. If not checked and dealt with immediately, it causes permanent damage which is very costly to repair.

Dangerous Slick Conditions

Sweating on smooth sealed concrete creates a dangerously slick surface. You can use an acrylic sealer or concrete coatings to make it slicker-resistant.

How to Determine the Cause of Sweating on Concrete Floor

You can easily determine whether the problem of sweating is from humid air from outside or moisture from underneath.

Try this: All you need is tape and a 16-inch piece of square-shaped plastic.

  • When the floor is dry, tape a square-shaped plastic, ensuring the edges are completely sealed.
  • Wait until the floor shows signs of wetness.
  • Remove the taped plastic and check the nature of the wetness.
  • If the sweating is on the rest of the floor and the patch is dry it indicates that the cause is due to humidity from outside, if the plastic is wet, but the floor is dry, it’s an indicator that the sweating is due to rising damp.

How do you Fix Sweating on Concrete Floors?

As you’ve seen, sweating is hazardous. It is important to make sure you deal with it before incurring high costs to repair.

  • Control the temperature of the room. Turn down/Up the air conditioning to keep the floor heat level the same as the room level
  • Use dehumidifiers to remove moisture from the air to reduce condensation.
  • Seal the concrete with a penetrating sealer to keep away moisture.
  • Make sure you use a water barrier during floor casting.

If you have noticed the problem has already occurred, you can consult a concrete consultant.

ALSO READ: Why is my vinyl floor Turning Yellow?

Leave a Comment

Your email address will not be published. Required fields are marked *