Moisture coming up through concrete floor

Water seeping through a concrete floor can be a serious problem. Not only can it cause damage to items stored on the floor, but the resulting moisture can lead to mold and other issues. What is the best way to stop the seepage?

To stop water from seeping through a concrete floor, you need to find out where it’s coming from. Water can seep through excessive hydrostatic pressure or structural problems in the concrete, and sealing it might not solve the problem. Finally, check that the problem is seepage and not condensation.

Concrete floors in a garage or basement should not be wet, and excessive moisture traveling through concrete can damage them, so you’ll need to isolate the problem to take appropriate steps. Keep reading to find out more.

What Causes Water To Seep Through Concrete?

Substances impermeable to water include plastic, metals, and glass. Concrete, on the other hand, allows water to travel through it. Water evaporation during the setting process enables air pockets and veins to form in concrete, which allows water to travel through concrete.

Water can seep through concrete through an imbalance of relative humidity. The direction moisture moves is determined by the humidity in the concrete and air, so if the concrete has higher relative humidity than the surrounding air, it will release moisture into the air.

It will also absorb moisture if the relative humidity of the surrounding air is higher.

Moisture can also seep through concrete through hydrostatic pressure or the pressure that water exerts against objects and surfaces. Generally, the deeper the foundation, the more susceptible basement concrete flooring is to water seepage problems. The following are the most common reasons for water seepage in a basement.

• Your house sits on a hillside, and water runs down to your home.
• The house was built at or above the water table.
• Water cannot drain from the soil due to its high clay content.

Don’t be fooled into thinking that if your concrete dries out, it will not be damaged. Both moisture content and movement can damage it, and you need to take the necessary steps to prevent them.

Signs That Hydrostatic Pressure Is Causing Water Seepage

If you live in an area with frequent and heavy rains and your home sits on a slope, hydrostatic pressure is naturally increased. Diversion techniques, which will be discussed later, might help.

However, if your home is built on flat land, there are other signs that you could be dealing with hydrostatic pressure:

• Standing water in your yard, suggesting soil saturation.
• Water entering the bottom of a 2-4 feet deep trench or hole in the ground.
• If water enters your basement, it is coming from numerous directions.
• There are no visible cracks on the floor.
• Your neighbors are having similar problems.

If water is seeping through your basement floor and you seal it, the simple fix could lead to additional problems unless you take steps to reduce the pressure. Here are a few suggestions.

Check Your Gutters

Gutters are supposed to drain water away from a house. However, clogged gutters can cause water to run down the side of a house and against the foundation. In the worst-case situation, the gutters can pull away from the fascia board. If that happens, water can enter your home and cause damage to roof rafters and your walls as well.

Add gutter spout extenders to the gutter system. Flexible extenders give you more control over how you will divert water from your home.

Install a French Drain

French Drains relieve pressure on a foundation by diverting water away from a house and replacing the compacted soil around the foundation.

A French Drain consists of an underground perforated pipe surrounded by gravel or small rocks. The trench needs to start where the hydrostatic pressure is strongest and then slope downward away from your house.

How deep to dig the trench depends on whether the water pressure is due to runoff from a hill or your basement is below the waterline.

If runoff from a hill causes excess water pressure, then the trench can be shallow. However, a French Drain needs to be dug deeper if the problem is due to a high water table.

Installing a French Drain is something a homeowner can do, but it can be time-consuming and requires trench digging. You can rent a mechanical digger for deeper channels or consider hiring professionals.

Inspect Your Landscaping

The soil around your house should slope away from it. So, first, check the slope of the land.

• Shrub and flower beds close to a house slope toward it, so the soil needs to be built up. The soil should slope away from the foundation by 1 inch (2.5 cm) per foot.
• If a lawn was not properly graded, it might need to be regraded. However, doing so requires lots of dirt and heavy equipment and would be best left to landscape specialists.
• The soil could also be compacted or contain excessive clay. Adding organic material to clay soil can provide some relief, but improving drainage in clay soil through organic material is a slow process.

Before you grade a lawn or amend the clay soil, install a French drain and see if that removes enough hydrostatic pressure.

Check for Underground Erosion

Use a hammer to tap lightly on the slab where you spot moisture. A slight echoing sound could indicate that you have a hollow pocket under the slab, and the weight of the concrete has caused a crack.

How To Keep Water From Coming Through a Concrete Floor

If you have concluded the cause is not hydrostatic, then fixing water seepage requires several steps.

• Cracks and seams need to be repaired. Use a concrete repair kit for the cracks and a cold seam sealant for the seams.
• Test how much moisture is in the concrete with a calcium chloride test, available at home improvement stores or online.
• Use the results of the test to decide on which type of waterproofing floor sealer to use.

Your Concrete Floor Could Be Sweating

It is possible that the water is not seeping through the concrete but that your floor is “sweating.” A damp concrete floor can be caused by condensation from warmer moist air encountering the concrete, just like the outside of a glass sweats on a hot day.

For this to occur, the concrete floor needs to be colder than the air. The air might have cooled to the same temperature as the concrete, which is most common during the spring in areas that experience cold winters.

Also, salt is hygroscopic, meaning it attracts water. Therefore, salt deposits on concrete can attract moisture from the air onto the concrete. If you live in an area where roads are salted in the winter, you could be bringing salt into the garage, and that salt will pull moisture from the concrete.

Sweating is less likely to occur on a concrete slab inside a house, but it does happen. Here are the conditions in which it might happen:

• The floor is colder than the dew point temperature of the air, and warm, humid air enters the house.
• A concrete floor with high moisture content has a strongly cooled surface.
• There might be no vapor retardant under the slab.
• A resilient floor covering such as vinyl flooring can have extremely high humidity levels.

These could be due to a concrete slab being framed before being cured or because the floor lacks a vapor barrier.

However, you should not ignore this problem. A sweating concrete floor can lead to mold, or even worse, it can lead to swelling reactions caused by the alkaline used in cement paste, a condition known as “concrete cancer.” Consult with a concrete expert on how to correct this situation before your slab is permanently damaged.

Sweating can also happen on the floor of a basement, which occurs in the summer when warm and humid air enters the basement. As the air cools, water will condense, landing on the concrete.

Testing for Sweating

If you lift a box or mat and the underside is dry while the rest of the floor is wet, the cause might be condensation or sweating.

To determine if your concrete is wet from sweating, use the following test:

1. Wait until the concrete is dry.
2. Cut a 16 x 16 square piece of plastic sheeting.
3. Securely tape it to the garage floor, sealing all four sides so there are no air gaps.
4. Let it sit until your concrete appears wet.

When your concrete looks wet, take up the plastic. Your floor is sweating if the concrete under the plastic is dry. However, moisture is seeping through your floor if you find moisture under the plastic.

How To Fix a Sweating Floor

To stop a sweating floor, you need to change the conditions that cause the floor to sweat. These could include one or more of these steps.

• Use a dehumidifier to remove moisture from the air. For a dehumidifier to work, doors and windows need to be closed.
• Improve circulation over the floor. A fan aimed at the floor keeps the air from being able to rest long enough to condense.

Bottom Line

Before attempting to fix the problem, determine its cause so that you pick a solution that will fix it without creating additional problems. Once you have isolated the problem, decide whether you can fix it yourself or consult with an expert.

Sources

• Hygroscopic Cycle: Hygroscopic Compounds
• Sciencing: Substances Impermeable to Water
• University of Nottingham: Hydrostatic Pressure

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