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DIY Guide: How To Seal Basement Walls

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Author Icon Written by Angela Bunt Updated 03/21/2024

Even finished basements can have moisture problems, whether it’s a musty odor or standing water on the floor. Minor dampness can often be solved with a dehumidifier and sealant, but persistent moisture problems may require a new drainage system along with basement waterproofing solutions

We’ll outline some strategies for interior waterproofing and list the major signs that more extensive solutions are necessary. We’ll also offer some tips for finding the right basement waterproofing contractors for your needs.

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Foundation Crack Repair

Foundation crack repair costs between $250 and $800.

Side of house with serious foundation damage.
Foundation Leak Repair

Depending on severity, leak repair can range from $2,300–$7,300.

Sinking concrete foundation in need of mudjacking leveling repai
Sinking Foundation Repair

The average cost for sinking foundation repair ranges from $600–$3,000.


Understanding Basement Water Issues

Water problems in basements and crawl spaces are far from unusual since these areas are often located below ground. If the basement walls are in contact with the water table or your yard has poor drainage, groundwater can seep right through the concrete. Over time, the hydrostatic pressure exerted by wet soil against a foundation can cause even concrete walls to bow and crack. Settling and shifting soil can also cause cracks in the basement and foundation walls.

Wall cracks lead to water seepage, which causes a damp basement and all the problems that come with it. A humid environment encourages mildew and mold growth, which leads to musty odors and potential respiratory hazards from mold spores. Water damage to a foundation can create or exacerbate a home’s structural problems and, in the worst-case scenario, cause basement walls to collapse. Foundation repair costs are typically very high, so it pays to waterproof your basement before this damage can happen.

Assessing and Preparing the Basement

If you’re already dealing with basement dampness, the first step is finding the problem’s source.

Inspecting Basement Walls for Damage

Try to identify the leak’s source, particularly around mortar joints, pipes, window wells, and other weak spots. Some cracks and gaps will be obvious, but concrete is porous, so water can seep directly through walls, causing damp streaks. If you’re not sure whether water is seeping through, tape a 1-foot square of aluminum foil to the wall. Peel it off after 24 hours. If the side facing the wall is damp, water is coming through from outside. If it’s dry, humidity from elsewhere in the room is the problem.

Dealing with Efflorescence and Mold

The white, powdery substance that forms on unfinished concrete floors and walls is called efflorescence. It’s an accumulation of salts and minerals that forms after water evaporates, and it’s not easily wiped away. Instead, you’ll have to use muriatic acid and a wire brush to remove the efflorescence. This is a diluted but still caustic form of hydrochloric acid, so work carefully and wear protective gear.

You should also remove mold before applying sealants. Remove and dispose of any moldy drywall, textiles, or other porous materials. On concrete, apply a mold treatment spray and scrub. Make sure you wear respiratory protection. If the problem is widespread, contact a mold remediation professional. The Environmental Protection Agency recommends contacting professional remediators for patches of mold of 10 square feet (a 3 foot by 3 foot square) or larger.

Removing Standing Water

If the basement is flooded, you must pump out the water before you can begin sealing cracks. Standing water greatly increases the risk of electrical shock when using power tools. Use an extension cord to plug the pump into an upstairs outlet and extend the drainage hose so that the water is discharged outdoors. When the water is gone, allow everything to dry thoroughly before proceeding with the next steps.

Sealing Techniques and Products

Once the space has been cleaned and prepared, you can start waterproofing basement walls. 

Choosing the Right Sealer for Basement Walls

You have a number of waterproofing products to choose from, so make sure you use the proper sealant for the task. Hydraulic cement is most useful for filling large cracks and gaps in basement floors and walls, as it expands and sets quickly.

For larger surfaces, silicate-based concrete sealers create a chemical seal with unfinished concrete that blocks moisture. However, it won’t stick to painted surfaces, so you may need to strip paint or other coatings before applying it.

Caulking and Sealing Cracks

For smaller cracks around 1/4-inch or less, caulk is usually effective. Make sure you use a silicone caulk that adheres to masonry, and check around all concrete penetrations such as pipes, windows, and doors where leaks are most likely to occur.

Applying Waterproofing Paint

Waterproof paint alone won’t stop substantial moisture problems, but it can be applied atop hydraulic cement and concrete sealer as well as previously finished surfaces. This makes it a good final step once sealer has been applied and cracks are patched. Here’s how to apply this waterproof coating.

  1. Choose a masonry, epoxy, or acrolein elasticized paint and purchase enough to cover your basement.
  2. Check the manufacturer’s instructions to see if any protective equipment is necessary. For example, some anti-mildew paints must be handled with care.
  3. Wait for a day when the temperature is above 40 degrees Fahrenheit and there’s no rain forecasted for the next 48 hours.
  4. Use a roller or brush to apply a thick coat of paint, ensuring it fills all surface holes.
  5. Let the paint dry completely, then add a second and third coat as per the manufacturer’s instructions.

Sump Pump and Drainage Considerations

If standing water in the basement is a recurring problem, you may want to install a sump pump and improve your yard’s drainage as part of your waterproofing system.

Installing and Maintaining a Sump Pump

There are two types of sump pumps. Pedestal pumps have an elevated motor and can sit in a pit or on the basement floor. They’re less expensive and easier to repair, but they’re also less powerful. Submersible pumps sit at the bottom of a lined pit and are priced higher, but they’re more effective. If you live in an area that’s prone to flooding, a submersible pump is a better long-term choice.

Importance of Gutters and Downspouts

Your home’s gutter system performs the important function of directing rainwater away from your home’s foundation. This prevents water from pooling and causing foundation damage and a wet basement. If your gutters are clogged or damaged, they may not be able to function properly, so it’s a good idea to clean your gutters about twice per year.

Foundation Repair and Additional Measures

Unfortunately, interior do-it-yourself (DIY) waterproofing may not be enough for severe or recurrent moisture problems.

Recognizing Foundation Issues

Homeowners can repair small cracks in basement walls and apply some interior waterproofing measures, but these will only be short-term solutions if the problem is a cracked or leaky foundation. If moisture problems persist or if you start noticing structural issues like uneven floors, it’s time to call in the pros. Note that horizontal cracks in a foundation are signs of a far more serious problem than vertical cracks. It’s possible to find affordable concrete slab repair and replacement, but this must be handled by professional contractors.

Exterior Waterproofing Techniques

Solutions that improve yard drainage are generally expensive and disruptive, but they may be necessary. The ground around your home can be regraded to direct runoff away from your foundation, or you can install a drain tile system to collect and pump away water. Also called a French drain or perimeter drain, this system involves digging a series of trenches and filling them with perforated pipes.

Another exterior basement waterproofing method involves encapsulating the foundation in a vapor barrier. There are plastic vapor barriers that can be installed in a basement’s interior, but a rubberized asphalt exterior barrier is one of the most effective waterproofing methods out there. Because it requires excavating around your foundation, installing a vapor barrier is a job for professionals.

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DIY vs. Professional Basement Wall Sealing

Most of the interior solutions listed above are reasonably easy home improvement jobs. However, the key lies in knowing when the problem is so severe that it requires a professional.

DIY Basement Wall Sealing

Masonry caulk, hydraulic cement, and waterproof paint are all solutions that you can purchase and apply yourself. Waterproofing contractors can charge up to $200 per hour, so you’ll save quite a bit of money by fixing modest water problems yourself. Waterproof paint usually costs about $1–$8 per square foot, and concrete sealant is usually around $3–$9 per square foot.*

*Cost data sourced from Angi.

Below is a video with more basement waterproofing details and instructions:

Professional Basement Wall Sealing

If your moisture problem is severe or keeps coming back, you’ll need more extensive solutions that only professionals can provide. Unfortunately, these solutions are often expensive, since many require below-grade excavation and specialty materials. The benefit of these more drastic measures is that they protect your investment in your house in the long term. Better drainage and exterior vapor barriers will permanently prevent basement and foundation leaks and the water damage they create.

How To Hire a Pro

When deciding between waterproofing contractors, here are some steps to take.

  • Waterproofing contractors don’t require a specialized license, but anyone who does work in your home should be bonded and insured.
  • Ask about specific solutions based on your yard’s grade, soil type, and foundation’s condition.
  • Look at the company’s Better Business Bureau (BBB) webpage to see its rating and accreditation status. You can also see any outstanding customer complaints.
  • Research customer reviews on sites such as Trustpilot and Yelp. Seek references from previous customers.
  • Ask about workmanship and material warranties.
  • Get quotes from at least three local contractors before making your choice.

Our Conclusion

Basement moisture problems can range from mild humidity issues to serious signs of foundation damage. You should include basic waterproofing measures as part of a basement’s finishing cost, and ensure you find and remedy the source of any existing leaks. If the leaks keep coming back or the problem doesn’t improve, call a professional to take more comprehensive measures.

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FAQ About Sealing Basement Walls

How can I tell if my basement walls need sealing?

Here are some signs your basement walls need to be waterproofed:

  • Excess condensation on ducts or pipes
  • Mold, mildew, or efflorescence
  • Musty or stale odors
  • Noticeable humidity or dampness
  • Soft or discolored drywall
  • Water tracks or streaks on walls

What are the common causes of basement water leakage?

The following are usually responsible for basement water leaks:

  • Blocked gutters and downspouts
  • Foundation cracks
  • Interior pipe leaks
  • Poor yard grading and drainage

Can I use waterproofing paint alone to seal my basement walls?

Waterproof paint may act as a temporary fix, but unless the moisture problem is very mild, paint alone is unlikely to solve it. 

How often should I reseal my basement walls?

According to FamilyHandyman.com, interior basement waterproofing tends to last about 10 years, but it will ultimately depend on your yard’s drainage and soil type.

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