Eliminating a damp basement

How to Seal Your Basement from Outside Moisture

by Benjamin Roussey


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Basement moisture can be a serious problem. A damp basement can not only be musty and depressing, but the moisture can cause damage to any furniture or electronics stored there. Moisture can also lead to mold formation and gradual weakening of the building foundation. If you have a basement moisture problem, do not put off repairing it.

Causes of Basement Moisture

Standing water, peeling wall paint, rotting wood, and rusted appliances are signs that you have a moisture problem in your basement. The two common causes are water seepage and condensation. Seepage occurs when water passes through the basement walls or floor. Condensation is primarily found on the walls and occurs from the cooler environment in basements.

A small amount of seepage or condensation can be easily fixed using a dehumidifier. If that doesn't solve the problem, you'll need to seal the walls and/or floor to prevent seepage.

Inside vs Outside

The decision on whether to waterproof from the inside or the outside depends on the amount of seepage. Minimal seepage calls for waterproofing from the inside. It's less expensive than outside waterproofing, so it's usually your first choice.

Concrete and Silicate Waterproofing

Waterproof coating and sealers are available for all types of interior walls. Concrete waterproof coating is suitable for unpainted concrete and masonry walls. It has to be applied with a heavy brush with bristles made of Tampico, a natural fiber. Silicate-based concrete sealers are also meant for unpainted and unsealed walls. After applying two coats of this sealer with a brush or roller, you can paint over it.

Waterproofing Paint

Another inside option is waterproofing paint, which is similar to regular wall paint. To be effective, it must have a thicker application than ordinary paint. That means you will need at least double the quantity of paint you would normally use. One advantage is that it can be applied over surfaces that have already been painted. The cost is in the range of $30-$50 per gallon.

While you're at the hardware store, be sure to get some polyurethane caulk to fill small cracks and gaps before applying the coating or sealer. Check for leaks where the walls meet the floor. A double layer of waterproof coating at this spot is a good idea.

Some cracks and holes are too large to be filled with caulk and paint. Use hydraulic cement to plug those up. Hydraulic cement is used because it sets up wet and expands to ensure a good fit. After you've filled the crack/hole with hydraulic cement you can paint.

Exterior Walls

If you choose to waterproof the exterior of walls, you'll need to dig all around the house up to the depth of the foundation walls. Then use a waterproof coating much like you would on the interior. In severe cases, you'll want to use a membrane and drainage panels. The panels must lead to an exterior drain at the bottom of the foundation and divert the water into a storm drain. This work is beyond most do-it-yourselfers and you may want to call in a professional.

Importance of Proper Drainage

Many basement leaks are a result of improper drainage conditions near the house. Take steps so that no water collects near your foundation. Wherever possible, slope the soil away from the foundation so that any excess water drains away from the house. Gutter drain spouts should have extensions that direct the water away from the basement walls. The gutters must be kept clean to prevent them from filling up and overflowing near the foundation. Certain landscaping features can also cause trouble. For example, brick or stone edging around flower beds near the foundation wall can prevent water from draining away.

Being aware of potential leak causes and adopting some prevention measures can help you save a significant amount of time and effort in the future. A dry basement is extra space that you can use and will also enhance the value of your home if you ever put it on the market.


Benjamin Roussey is from Sacramento, CA, and grew up doing all varieties of home improvement projects around the home since his parents did not hire contractors or outside help to maintain their home or vehicles. As a result, he has acquired a multitude of home handyman skills in plumbing, carpentry, electrical and everything in between. He also has two Masters degrees and he served four years in the U.S. Navy.

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