How to Waterproof Your Basement

water in basement
Before you write a check to a contractor, it's entirely possible you can remediate a wet basement situation yourself. youngvet/Getty Images

When it rains, it pours and when that rain pours into your basement, it might look like one of the Great Lakes. If that's the case, you might be tempted to call a contractor and have them install an expensive interior drainage system to pump the water out and to mitigate it from happening again. Before you write the check, it's entirely possible you can remediate the situation yourself.

It is not unusual for basements to become wet, or at the very least, moist. In fact, the American Society of Home Inspectors suspects that 60 percent of all homes in the U.S. have wet basements. And a wet basement, as you'd probably suspect, is not a good thing. It can lead to a variety of problems, including mold. Water in a basement can also rot away a home's drywall and framing [source: Wagner].


There are many reasons why your basement might not be dry, but the main culprit is that water from rain or even snowmelt is seeping in from the outside through a leak (or leaks) in the foundation. Moreover, there might be a leaking pipe or pipes dampened by condensation [source:]. (More on how to fix that later.)

For now, let's assume that rainwater and snowmelt are the culprits. When it rains, or the snow melts, the water runs off your roof down toward the foundation of your house. Water, being water, always flows to its lowest level — an immutable fact of physics. It will saturate the soil near the house and seep under cracks in the foundation. Water can also penetrate concrete walls.

So the first step in mitigation is to figure out why your basement floods. If your basement leaks after a heavy rainfall, or in the spring when the snow melts, then the answer is pretty self-evident: Water is coming from the outside [source:]. The next step is to locate where in your basement the water is migrating. Once you've determined both of these, the next step is to stop the flow. We'll talk more about how to do that on the next few pages.


Whisk the Water Away

If your house doesn't have gutters, consider installing them or having them installed by a professional. David Hartwell/Getty Images

The key to solving a leaking basement problem is to direct the water away from the house's foundation. Gutters can help a lot. Gutters catch rainwater and whisk it away through downspouts. If your house doesn't have gutters, consider having them installed. And this next step is critical: Attach horizontal drain extensions that are at least 4 feet (1.2 meters) long to the downspouts. These will direct the water away from the edge of the home's foundation and away from the basement [source:].

If you already have gutters, clean them. Gutters won't work if they're crammed with leaves and branches. Specifically, unclog the mess where the gutters meet the downspouts. If not, when it rains, the water can cascade like a mini Niagara Falls straight down to the edge of your foundation [source: Brasler].


Another way to direct water away from your home's foundation is to regrade the ground away from the foundation. This is more involved than simply adding gutters and downspouts, but it can help. The slope should be at least 6 feet (1.8-meters) wide, dropping down to about 4 inches (10 centimeters) away from the foundation. You can also cover the slope with plastic sheeting for added protection. Hide the sheeting with dirt and simply plant grass over it, or throw mulch or stone on top [source:]

Patch Leaks and Waterproof Walls

waterproofing floors
You can easily waterproof your basement walls and floors. It rolls on just like paint. BanksPhotos/Getty Images

Patching leaks in your foundation probably won't stop all the water from coming into the basement, but it can't hurt. To do this, you will need hydraulic cement. Hydraulic cement puts a cap on the water coming through the walls. It sets and hardens extremely quickly. Once you mix it, it's workable for only about 10 to 15 minutes, so be sure you're ready to use it before you mix.

First, clean the surface of the foundation. If there's dirt, dust or oil, it will hinder the cement from bonding. Wire brushes work well [source: Rodriguez]. Next, get rid of all the loose particles on the foundation no matter how large. Use a trowel to slather the cement on the surface.


You can also waterproof your walls. Waterproofing goes on like paint, but don't spread it too thin. The idea is to put enough waterproofing so that it sinks into the pores and cracks on the walls. Also, brush the waterproofing on in all different directions, like the Karate Kid did when painting Mr. Miyagi's house: wax on; wax off. This will ensure that the waterproofing goes to where it's needed. Of course, clean the walls first with the aforementioned wire brush. Then go to town. Once the first coat is dry, apply a second coat [source:].

You can also damp proof the outside wall of the foundation with a tar- or asphalt-like substance. If you have a newer house, chances are the foundation is already damp proofed. But keep in mind, damp proofing will fail in time. Also, waterproofing and damp proofing are not the same. You want to damp poof your basement to keep out soil moisture. That's the stuff that gives you that awful, musty smell [source: Basement Systems].

Foundation waterproofing membranes are also an alternative, though this job is expensive and best left to the professionals. Made from rubberized asphalt attached to a waterproof polyethylene film, the membranes have to be installed to the outside of the foundation. It works best in full basements, as opposed to crawl spaces [source: Home Advisor].


Controlling Condensation and Humidity

foam insulation
Wrapping your pipes with foam insulation will help stop condensation from forming around them. nsj-images/Getty Images

As mentioned before, condensation and humidity can make a basement damp. Condensation occurs when water from cold pipes reacts to warm air. If you don't believe that, go into your basement on a humid day and watch the condensation drip onto your floor.

To stop condensation from forming, you can install foam pipe insulation around your pipes. It's cheap and easy to install. The foam is slit open lengthwise so you simply slide it onto your pipes. Cut off any excess with a scissors or utility knife. For those in northern climes, the insulation will keep your pipes warm so they don't freeze in the winter.


You can also insulate the walls of your basement to help prevent condensation. Foam tongue-and-groove insulation panels are available that don't require a master's degree to install. However, and this is a big however, don't insulate anywhere water is seeping in. You're just going to make things worse by giving mold a fertile ground on which to multiply [source:].

Humidity is also a problem and there's not much you can do when it's humid outside. But you can reduce the level of humidity by using a dehumidifier. Some dehumidifiers are labor intensive. When they're full you have to drain them. However, some dehumidifiers allow you to hook up a hose that you can run to a floor drain. Another thing you can do to reduce the amount of water vapor in the basement air is to make sure the exhaust line from your dryer is sealed tightly. All you need is duct tape to close up any openings.

Of course, the best way to waterproof your basement is to install a drainage system. The system includes tubing and a sump pump, which moves the water out. These systems are expensive, though the cost depends on the size of your basement and how much work is required for installation. The concrete floor has to be broken up; tubing and edging have to be installed; and then the floor has to be put back together.

Your best advice may be to talk to a contractor to find out what can be done to keep your basement dry. There are other avenues, aside from these we've mentioned here, that could make more sense for your situation. But no matter what, you should definitely get that basement dry.


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More Great Links

  • Basement Systems. "Damp Proofing the Outside Foundation Walls." (Aug. 22, 2018)
  • Brasler, Kevin. "Wet basement? Try these cost-effective solutions before calling a contractor." The Washington Post. Jan. 18, 2017. (Aug. 22, 2018)
  • Damp Basement. (Aug. 21, 2018)
  • 9 Affordable Ways to Dry Up Your Wet Basement for Good! (Aug. 22, 2018)
  • "Seal a Basement or Foundation." (Aug. 21, 2018)
  • Rodriguez, Juan. "The Uses of Hydraulic Cement and How to Apply." The Balance Small Business. May 17, 2018 (Aug. 22, 2018)
  • Wagner, John D. "Drying Out a Wet Basement." This Old House. (Aug. 22, 2018)