Why Is My Carpet Wet When My House Is On A Cement Slab?

Tom Gaffey
by Tom Gaffey

Wet carpets in the home are a pain to deal with. They are a breeding ground for mold and other bacteria. This issue is difficult enough to deal with when you know the reason your carpet is wet.

When the carpet is on a cement slab and gets wet for what seems like no reason there may be an even bigger issue than wet carpet.

There are several reasons why carpet becomes wet when it is on a cement slab. First, you should check for any signs of a leaking or broken pipe. Check for cracks in the foundation where groundwater can seep through the cement slab. The wet carpet can also be a result of dew point condensation if the outside weather is hot and humid.

When you notice wet carpet on a cement slab you should immediately investigate further. Some of the root causes may be mild, like very high humidity on a hot day. There are other causes that can be serious problems. A wet carpet on a concrete slab can be a warning for a much bigger issue that should be handled immediately by a professional.

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Leaking Pipes

If you notice your carpet that sits over a cement slab is wet you should make sure you do not have a leaking or busted pipe. Leaking and broken pipes need to be dealt with as soon as they are identified.

The longer leaking and broken pipes go untreated the more damage they cause. There are several ways to know if you have a broken or leaking pipe under your foundation.

  • Increased Water Bill. A significant spike in your water bill should be an instant red flag. Unless you greatly increased your water usage in that month there is a good chance water is escaping somewhere it should not be. Be sure to check all visible pipes, sinks and outdoor hoses first. If they are working properly there may be a leak you can not see. 
  • Hearing Running Water When You Should Not. If all your sinks and appliances that use water are off you should not hear running water. When you hear water moving through your pipes or a distant sound of running water you should investigate further. If you can not find the source of the sound but it persists, contact a plumber.
  • Cracking Foundation. A cracking foundation is a sign of several issues. A broken pipe underneath can cause damage to the cement slab and crack it. If you notice cracks in the cement foundation along with water on your carpet on the cement slab you should contact a plumber immediately. 
  • Decreased Water Pressure. If your water pressure seems to decrease out of nowhere you may have an unseen leak. If decreased water pressure coincides with you noticing wet carpet on a cement slab you should investigate further.

Excessive Groundwater and Cracked Foundation

If you notice wet carpet on top of a cement slab you may also take your weather and surroundings into consideration. Your home may have a higher groundwater content than normal. When you live in a wet and flat area without significant drainage this may be particularly true.

Cement can crack over time. If the ground around your cement foundation is frequently saturated water will try to push through the cracks in order to find a place to travel. Eventually, water can move from the wet ground onto the cement slab that sits under your carpet.

Dew Point Condensation

Hot and humid air can often cause the cement slab under your carpet to “sweat.” Cement can collect moisture on hot humid days through a process called dew point condensation.

Dew point condensation occurs when warm moist air encounters the cool dry concrete. Just like water collecting on a cold water glass outside, water can bead up on the concrete floor. This condensation can cause a wet carpet if the carpet sits on top of a concrete slab.

Used The Wrong Vapor Retarder

When you install flooring and walls to a home you often install a vapor barrier over the building material. A vapor retardant often allows for some moisture movement, but helps control the amount of moisture that can permeate the layer.

If the wrong type of vapor retardant is placed on your concrete slab it can result in wet concrete. There is potential for moisture buildup if there is no seal protecting the concrete from outdoor elements that sit on the other side.

Fixing The Problem

Once you find the reason why your carpet is wet on a cement slab you can make steps to solve the issue. The solution, however, will vary depending on why the cement slab became wet in the first place.

Seal The Concrete

  • Wash And Clean The Concrete Floor. First, sweep the floor to remove any dirt. Next, wash and scrub the floors to remove any grime or oil-based stains from the floor. Allow the floor 24 hours to dry.
  • Fill Cracks using concrete crack sealer. Apply the crack sealer with a putty knife. Refer to the sealer label for the exact drying time needed for the crack sealer.
  • Remove Any Existing Sealant. First test the concrete to see if there is sealer on the concrete. If there is, use a stripping agent to strip the sealant from the concrete. The old sealant will need to be scraped off and the floor must be scrubbed and dried again.

Testing For Sealer: Pour a cup of water onto the concrete. If it soaks in it has not been sealed. If it beads up then it has been sealed.

  • Apply First Coat with a paint roller after the floor is stripped, cleaned and completely dry. Check the sealant container for drying times. Allow the first coat of sealant to dry completely.
  • Apply Second Coat Of Sealant. Apply a second coat of sealant to ensure there is a secure layer of protection. Paint the second coat at a right angle to the first coat to ensure thorough and even coverage. Allow time to dry.

Purchase a Dehumidifier

If your carpet is damp over a cement slab a dehumidifier may be the solution. When the moisture on your concrete comes from dew point condensation the best way to eliminate the moisture is to reduce the humidity.

Dehumidifiers are designed to lower the humidity in the space they occupy. Be sure to purchase the correct dehumidifier for the size of the room in question. Dehumidifiers help decrease the appearance of mold and dust mites in addition to preventing damp carpets on concrete slab.


Related Questions

How Do You Kill Mold On Concrete?

When concrete stays damp and is not exposed to UV light, it can grow mold. Pressure washers are a common tool in combating mold on concrete outdoors. When you have mold on indoor concrete there is a mixture using common household cleaners that can effectively kill mold.A combination of bleach, laundry detergent and warm water is a very effective solution in combating mold on concrete. Use protective gloves and a sponge to scrub the solution on the moldy area. Allow a few minutes for the bleach to break the mold down. Continue to scrub until the mold is gone. Be sure to rinse and wipe the area with warm water before allowing the floor to dry.


How Long Does It Take Concrete To Dry?

Concrete often appears to dry completely in a day or two. It is not uncommon to walk on concrete just days after it was poured. Concrete does hydrate and harden significantly in its first 24 to 48 hours, but it takes approximately 28 days for concrete to fully dry. It is important not to cover concrete or move on to further construction steps until the concrete has dried fully.


How Do I Dry a Wet Carpet?

When your carpet is soaked with water it is important to dry it out quickly to avoid mold that can potentially ruin the carpet. Wet-Dry vacuums are designed for this exact purpose. Run the wet-dry vacuum over the affected multiple times. Place fans over the wet area to promote drying and air circulation.If you do not have a wet-dry vacuum you can sprinkle kitty litter over the affected area. Press the kitty litter into the carpet using towels and allow it to soak up the moisture. Use a shop vac to clean up the kitty litter and then aim fans at the damp area.

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Sealing It All Up

When you notice wet carpet on cement slab in your home it is important to address the problem immediately. If you avoid the problem mold can grow and the situation can get far worse and more costly to repair. If the problem is anything serious like a broken pipe you should contact a plumber immediately.

Sealing the cement slab creates a barrier that should block future moisture from reaching your carpet. If the problem is high temperatures and humidity you should look into a dehumidifier for any rooms that experience wet carpet.

Tom Gaffey
Tom Gaffey

Tom Gaffey is an expert writer who currently resides in Washington D.C. Tom has a passion for real estate and home improvement writing, as well as travel and lifestyle writing. He lived the last twelve years in Hawaii where he worked closely with luxury resorts and event planners, mastering his knowledge of aesthetics and luxury products. This is where he found his passion for home improvement and a keen interest in DIY projects. Currently, Tom resides in Washington D.C, and also working on his debut fiction novel.

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