What Causes Garage Floor Sweating and How to Stop It

A sweating garage floor is an annoying occurrence, not to mention a hazard. The moisture can cause the floor to be slippery, so the odds that you will have a slip-and-fall accident are significantly increased, for instance.

For many, the biggest negative impact of a sweaty floor is that it creates a musky odor that can be difficult to deal with. You want to do whatever you can to avoid a musty garage, because once you get one, it takes lots of effort to get rid of.

Sounds like your garage? There are ways to stop the moisture and sweating in their tracks!

What Causes the “Sweating” or Moisture on Concrete Floors?

First, you need to find the cause of your sweating concrete floors. Condensation and moisture beneath the slab are the most two common culprits, but it may also be caused by a drainage issue, too.

Condensation: When the floor is colder than the dew point temperature, moisture condenses. This is why “sweating” occurs in the warmer months and not in the colder months. When the concrete is cooler than the moist air that flows across it, temperatures collide. The colder concrete cools the air quickly. The cooling air drops below the dew point of the ambient air around it, and it condenses onto the concrete. The result is slick concrete flooring.

Moisture: And moisture beneath the concrete can eventually damage the surface. The water can cause the components of the concrete to break down and weaken. Mold and bacteria can also grow, making your garage’s interior unhealthy for you and your family. If this condition exists, you likely also have the same situation under your entire house slab, which can be a major concern.

Drainage: In some cases, your shed or garage might be built in a spot where it naturally gets runoff after a rainstorm, or especially in the spring if you live in a colder snowy climate. In this case, it is a drainage problem, not a sweating problem. The drainage issues are usually caused by a combination fo the ground’s grade next to your shed or garage, along with foundation materials that let the water in.  I once had a shed that was built-in to a hill, and the floor was wet every single spring because the water was trying to flow downhill and the shed’s concrete foundation could not stop it from coming in.  Floor type might also impact how your floor prevents basic water intrusion.

Determining What is Causing Your Wet Floor

water puddle garage

There are a few ways to determine what is causing your problem. The main thing for you to decide is, based on your observation, if you thing the moisture is from a sweating or drainage issue.

For a Sweaty Floor:

What You Need:

  • A heavy piece of plastic that is at least 16″ x 16″
  • Duct tape
  • A clean section of flooring

Step 1:

Choose an out-of-the-way place in the garage where the plastic can be used. The plastic has to stay in place until the next time you notice sweating, so do not place the plastic in a high-traffic area. Sweep the flooring clean of dirt and debris.

Step 2:

Place the plastic over the clean section of the floor and tape it down securely. You do not want air to be able to get under the plastic.

Step 3:

Leave the plastic taped to the concrete until you notice condensation again.

When the floor is damp, gently lift the plastic. If the moisture is on top of the plastic, you are dealing with condensation. If the plastic is moist on the bottom side touching the concrete, you are dealing with moisture beneath the slab condition.

For a Drainage Issue:

This process is a little less defined.  What I like to do is make sure I am starting with a dry floor — sweep the water out, and dry it with a fan if possible. Then, you need to observe where water is coming from.  This is best done with a time-lapse camera (most old $50 digital cameras have a nice time-lapse feature) or by checking the floor every hour or two, if possible.  You will see early-on where the water is coming from…. like a dam that is started to break.  If you wait until the whole floor is wet, it is hard to know where the problem began.

If you need to waterproof your shed base, or drain tile it, that can be a pretty involved job, but one that you likely will be happy you did.

Combating Condensation — The Most Likely Culprit for Sweating Floors

Condensation is the most likely cause of garage floor sweat. There are several different ways you can address this condition.

Tips from the Pros: If you are dealing with condensation, sealing the concrete will not stop condensation. Sealing the concrete may increase the slickness of the floor when condensation does form.

Lower the Humidity in the Room

The solution to your condensation may be as easy as using a dehumidifier. When the humidity is lowered, there will be less moisture in the air, which means less water will be available to condense on your floor.

Increase the Air Circulation

Fans circulate the air, which, in turn, stops the air from colliding with the cooler concrete and forming condensation. It also allows the area to be cooler, further battling the formation of condensation. Ceiling fans, shop fans, or wall-mount fans will work here.

Heat the Room

The cold temperature of the concrete clashes with the warmer temperature of the air and causes moisture. If you heat the room, you will heat the concrete and stop this problem. However, this isn’t generally recommended as condensation will usually occur in spring and summer — your garage is already likely warm or hot! Space heaters will make it unbearable for some, not to mention expensive.

Seal the Air Out

Our garages are typically not as tightly sealed as the other parts of our home. Under garage doors, there is often a gap where the door does not fully meet the concrete. Installing a door seal made for the garage door can reduce the problem.

Don’t Leave Your Garage Door Open

Many people have a habit of leaving their garage door open all day, making it easier for them or their kids to go in and out. If you live in a humid area, this is a bad idea because you are introducing massive amounts of humid air into the garage.  You are better off trying to leave the garage door closed as a default.

You can also:

  • Seal around windows
  • Install insulation in the walls or ceiling
  • Use spray foam insulation to fill in gaps or holes in the exterior

Consider Absorbent Mats

The concrete stays cooler than the air above it because concrete reflects heat instead of absorbing it. It takes longer for the material to heat up.Installing vinyl mats or interlocking garage floor tiles will absorb heat, stopping condensation in its tracks.

Seal the Concrete Floor

Sealing the floor is often a tempting step for many homeowners, but it should not be your primary way of combatting a sweaty floor. To be clear, sealing the floor treats the symptom and not the cause of the problem.  However, it can be a good way to keep some of the easy moisture from forming. It is best to have this done professionally, in my experience.

Combating Moisture Below the Surface

If moisture comes up through your concrete slab, you must apply a vapor barrier to stop it. The vapor barrier will stop the water from coming through.

If you plan to finish the floor with tile or a floor covering secured by adhesives, you need to know that moisture barriers often interfere with the adhesives of those products. There are products created to be used as moisture barriers with low permanence. They tend to be less likely to prevent future flooding if adhered correctly.

A sweating garage floor can be a nuisance and a danger. If you live in an area with high humidity levels, you are likely to see more condensation problems. To reduce the moisture, you have to level out the temperature between the air and the concrete or decrease the humidity level in the air so there is less moisture potential. Good luck!


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