Why Is My Garage Floor Sweating? [Fix It Now!]

One of the weirdest things I’ve seen as a homeowner is when my concrete garage floor appeared to be…sweating. 

Moisture accumulating on your garage floor can be caused by several reasons, from humidity in the air to water seeping up through the foundation. No matter how the moisture gets there, a slippery floor could be the least of your worries. 

This article will explain why your garage floor appears to be sweating and what you can do about it. 

Moisture on concrete floor looks like sweating

What Causes Garage Floor Sweating?

Most often, condensation is what causes your garage floor to appear to sweat.

Condensation occurs at a specific temperature (the dew point) when a gas turns into a liquid. 

In this case, humid, warm air comes into contact with your cold garage floor, causing the water molecules in the air to cool and form water droplets. 

This happens so often in the construction industry that they created a name for it: sweating slab syndrome.

For most of the country, sweating garage floors usually occur on spring days when the air is warm and moist, and the concrete is still relatively cool from winter. It also happens frequently in coastal regions where warm ocean air meets your considerably colder garage floors.

When the moisture evaporates, salt or other mineral deposits are usually left behind, which can damage your concrete floor over time. 

Is it Moisture Build-Up or Garage Floor Sweating?

Condensation isn’t the only cause of your garage floor sweating. Occasionally, moisture seeps up through the foundation instead of condensing from the surrounding air. 

Although it may look similar, this is a moisture issue rather than garage floor sweating.

Concrete floors are porous, which lends itself to water absorption from the surrounding soil. This is usually because the underground layer of concrete isn’t fitted with a moisture-resistant layer. 

In this instance, the moisture rises to the surface due to a lack of humid air above it. When temperatures aren’t warm enough to cause evaporation, the moisture could remain on the surface for some time, making your garage floor appear to be sweating. 

How to Test for Garage Floor Sweating

It’s easy to confuse a sweating garage floor with a moisture issue coming from beneath the surface. 

Thankfully, you can do a simple test to determine which problem your concrete floor has. 

First, you’ll want to get a section of clear plastic wrap. 

You may have some in your kitchen pantry. Otherwise, you can pick up some inexpensive polyethylene tarps at Lowe’s and Home Depot for around $10 each. 

Cut an eight-inch square section of the tarp for each area you want to test. Make sure that the section of the floor is completely dry before continuing. 

Using painter’s tape, tape the plastic wrap to the surface of your concrete garage floor. 

Leave a small pocket of air in between the plastic and the concrete. Make sure that all four sides and corners are sealed off with tape. 

Wait until you notice sweating in a different section of your garage floor. Then, remove the tape and examine the bottom of the plastic wrap. 

If the covered area is still dry, while the rest of the garage floor is wet, then your garage floor is sweating. But if the covered area is as damp as the rest of the floor, it’s likely due to moisture seeping up through the concrete. 

Five Ways to Stop Your Garage Floor Sweating

Unfortunately, you can’t fix a sweaty garage floor just by adding a clear coat or sealer. Because there are still temperature differences between the floor and the air, you’ll still get condensation, even if there’s an extra layer.

You’ll need to adjust the climate inside your garage to solve this issue. 

Here are five things that can help: 

Lower Humidity Levels

As I mentioned, warm, humid air touching the floor is the leading cause of a sweating garage floor. 

Humidity can negatively affect electronics and tools in your garage, so it’s well worth getting it under control. 

This means using a dehumidifier or moisture absorber to keep your garage’s humidity levels in check and reduce the likelihood of your concrete floor sweating.

Garages aren’t sealed as well as the rest of your house and are open to the outside air. That means a dehumidifier needs to work extra hard to keep your humidity levels in check. 

You don’t need to use a dehumidifier year-round. However, it will require you to monitor the humidity levels in your garage. 

Here in Central Florida, I only use my dehumidifier when the humidity inside is over 60%. Ideally, the humidity level should be less than that. However, I store any sensitive items in air-tight containers to protect them as much as possible. 

Think of a dehumidifier as an investment. When buying, select one rated for at least as large as your garage. Remember, a large, high-efficiency humidifier is usually more cost-effective than a cheaper, smaller one. 

Here are some standard garage sizes in North America:

  • One-car garage: Up to 384 sq. ft. 
  • Two-car garage: Up to 624 sq. ft.
  • Three-car garage: Up to 816 sq. ft.

Finally, every dehumidifier will need a dedicated electrical outlet and a drainage system. 

Many dehumidifiers allow you to attach a standard garden hose to allow the water to quickly flow outside. If not, you’ll need to consider adding a trench drain in your garage, so the moisture has somewhere to go. 

Lastly, keep the garage doors closed when the humidifier is running. 

Increase Air Circulation

In addition to decreasing humidity levels, increasing air circulation in your garage can go a long way in preventing your concrete floor from sweating. 

Scientists have observed a drastic reduction in condensation rate when air is moving. Even speeds as low as 1 m/s can reduce condensation by as much as 50%. 

One or two well-placed fans can help circulate the air in your garage and make it feel cooler as well. 

Depending on your garage layout, you can do this with one large fan or several smaller ones. Additionally, you can choose between purchasing an oscillating or ceiling fan to help you gain enough ground coverage.

The key is to place your garage fans correctly to maximize airflow.

Oscillating wall-mounted fans are great because they force hot air near your ceiling to mix with cooler air near the floor. Similarly, a ceiling fan is highly beneficial, especially for large garages, since it directly blows air toward the garage floor.

I had great success with one oscillating wall fan combined with a dehumidifier. Using both tactics almost eliminated the condensation on my garage floor.

Air King garage fan

Heat Your Garage

Depending on where you live, a garage heater is another way you can eliminate a sweaty garage floor. 

Since warm air needs to cool to the dew point to condense, heating the air is an easy way to stop that from happening. 

Admittedly, this may not be practical during summer or if you live in the South like I do. 

Concrete floors are poor conductors of heat, so it may take some time to notice any results. You may end up spending a lot on electricity to run a heater.

However, if you’re building a new home, or replacing your concrete garage floor, a radiant heating system under the floor may be the way to go. 

Several options are specifically designed for concrete surfaces, making them ideal for your garage floor. 

The one I prefer is the LuxHeat Mat Kit. It’s easy to install and can be configured in different sizes and layouts. 

Seal the Garage Off

I can tell you from experience living in Florida that closing the garage door isn’t enough to keep the humid air out. Even with the garage door shut and the lights off, I still notice seams of sunlight beaming around my garage door. 

If light can make it in, so can humid air.

It’s well worth the expense to replace the seals around and underneath your garage door. In extreme cases, you can even add an additional garage door threshold seal that attaches to your concrete floor. 

Replacing the seals around your garage door is relatively simple but can be time-consuming. Most garage doors have an aluminum rail along the bottom that the seal slides into. 

I recommend adding vinyl weather stripping on the top and sides of the garage door that prevents outside air from seeping in. In addition to preventing your concrete garage floor from sweating, they’ll also help prevent common garage bugs and rainwater from entering.

Additionally, any windows in your garage may also be a source of moist air entering your garage. 3M makes a specialized window sealing tape to keep all the elements outside. However, the garage door and windows must remain shut for this technique to work.

Overall, properly sealing your garage, along with using a fan and humidifier, will significantly reduce your garage floor sweating. 

Change Your Garage Flooring Plan

When all else fails, changing your garage’s floor surface can help. 

For instance, interlocking floor tiles or garage floor mats can help you avoid slipping on damp floors. 

Floor mats that are specifically designed for garages come in multiple styles and materials. 

Most are water-absorbing, which is perfect for industrial use. They’re designed to hold about a gallon of water at a given time which helps keep your garage floor dry whether it’s from sweating or your car is dripping wet from a recent car wash.

Some floor mats, such as the Armor All garage mats, are made from a polyester blend, making them slip-resistant, easy to clean, and highly durable. 

Wrapping it Up

The most common reason for your garage floor appearing to sweat is moisture from the air condensing on the concrete surface. 

However, your garage floor may be damp due to moisture rising from the ground through the concrete. 

This is a different issue from sweating, but still potentially damaging. This is caused by water seeping through the porous concrete layers underneath the surface.

You can reduce or even eliminate your garage floor sweating by adjusting the climate in your garage. This is commonly done by improving air circulation with an oscillating fan, eliminating humidity with a dehumidifier, and sealing the garage from humid air.

You should also take precautions to avoid storing things in a damp garage.

Photo of author

Tim Wells

Tim Wells, the founder of Garage Transformed, has been featured in dozens of home renovation publications, including BobVila.com, Home Stratosphere, House Digest, Livingetc, and SFGate. Since 2018, he has helped over two million people transform their everyday garages into something they can be proud of. He lives in Central Florida with his wife and bulldog.