Is My Garage Floor Sweating?

Posted by Mike Mincemoyer on Aug 7, 2015 1:51:00 PM

Is my garage floor sweating?

Concrete garage floors  with sweating slab syndromeIt’s one of those questions we get every now and then.   Often, the homeowner is unsure of what is happening, doesn’t know why it’s happening or what to do to prevent it.    Let’s take a quick look into what is often called Sweating Slab Syndrome.   This condition can apply to raw, unsealed concrete or to floors coated with epoxy systems, like our decorative chip, garage floor coating or even a DIY garage floor paint kit.

Hang Up, No Need to Call a Doctor!

First, you don’t need to call a doctor to diagnose the problem.   Your garage floor is not sick or contagious.  Here are the most common symptoms to determine if the floor is sweating:

1)      There is a build-up of moisture on the garage floor, almost like someone just misted the floor with water.

2)      If the concrete floor is uncoated (no epoxy or other polymer on the concrete), the concrete slab may be darker than normal and feel slick to the touch.

3)      There is a salt-like efflorescence on the concrete that has moisture or darkening around the salty deposits.

Yup, my floor is sweating! What is causing this?

Causes of Sweating Slab Syndrome

A concrete garage floor may sweat for one or more of the following reasons:

Get A Free Quote 1)      The most likely reason a garage floor will sweat is warm, moist air has entered from the outside and condensed water on the garage floor because the floor’s temperature is below the dew point. 

2)      Not as common a reason for sweating is salt deposits on the garage floor (left over from winter treatments) or natural salts found in the concrete mixture attract moisture from the air onto the concrete surface.   The hygroscopic nature of salt can even draw some of the moisture from the concrete itself.

3)      The least likely reason for a garage floor to sweat is due to hydrostatic pressure, whereby water vapor is being pushed up through the concrete slab at a rate faster than normal evaporation.   This is uncommon, as most residential garages have at least a stone base separating the concrete slab from the supporting ground, if not an actual plastic moisture barrier.

OK. Now we know what is causing my floor to sweat.  Who I do now?

Reducing Sweating on My Garage Floor

There are several approaches to reducing sweating slab syndrome, some of which are applicable only in commercial and industrial environments.   For a residential garage floor, here are the most common steps to take:

1)      As this most commonly occurs in the morning in late spring or early summer, do not leave the garage door open for any longer than necessary.  

2)      Clean residue and deposits off the garage floor.  Salt and other alkaline deposits will contribute to sweating, so a thorough cleaning will reduce topical alkali content.   In addition, a thorough rinse will ensure any soap residue is not left behind and contribute to slippery, slick conditions.

3)      If sweating continues to be problematic, get the air moving through the garage.   This may involve leaving windows open to allow more continual air flow and reduction of temperature differentials.   Sweating could also be dried quicker by use of a fan.

We normally get asked about a sweating floor only to find out that the homeowner opened the garage door at 6 am and left it open for a couple hours resulting in moist, morning air blowing in over the cold garage slab – often puddling more at the back of the garage where the slab is often colder.  - Jason, MD Operations Manager

The best way I have been able to explain it to customers is the "soda can" example. A soda can is designed to keep the liquid cool and the air out. Our coating acts like the can. So when the soda is cold any warmer/moist air passing over it is going to condense on the outside.   -  Zach, PA Operations Manager

Hope this helps.


Mike (with help from Jason & Zach - our Operations Managers) decided to write this article after answering this question for at least the 20th time since 2004.  

Topics: Garage Floor Coatings

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