Do-It-Yourself Basement Waterproofing

By RadonSeal | March, 2021


Easy DIY Waterproofing Solutions That Will Last

Wet or damp basements are the most frequent complaint of homeowners. Traditional, decades-old basement waterproofing methods have not passed the test of time: "Over 60 per cent of basements have moisture seepage in one form or another, while 38 per cent experience mold and fungus growth due to an elevated moisture level." – The American Society of Home Inspectors. Slab-on-grade buildings suffer similar moisture problems. Now, there is a better solution!

Improving Your Home's Health – For over 20-years our line of Penetrating Waterproofing Sealers, DIY Foundation Crack Injection Kits, Concrete Floor Repair Kits, and basement waterproofing and radon mitigating products have proven to be the ideal solutions for drying out basements. Commercial-grade, high-strength, long-lasting, and unique materials that continue to be trusted by building contractors and DIY homeowners nationwide. Products that can permanently waterproof and damp proof wet and leaking foundation walls and basement concrete floors. Helping to significantly improve the overall health of your basement and home.

The Permanent Concrete Sealer – RadonSeal Deep-Penetrating Concrete Sealer is not "your father's" waterproofing paint or sealer. RadonSeal differs from paints and membrane coatings by penetrating deep inside concrete (up to 4"), chemically reacting with free lime and alkalis, expanding within the pores and capillaries of concrete, and curing as a hard mineral. RadonSeal will seal your concrete internally against the transmission of capillary water seepage, water vapor and strong enough to seal against radon gas.

Why Basements Start Leaking Water

A hard-driving rainstorm or melting snow can temporarily raise groundwater levels and for every inch of rain, a 1,500 sq. ft. roof sheds almost 1,000 gallons of water. Rain gutters and downspouts get plugged up with debris. New houses have a problem with "reverse grading," which usually occurs several years after construction. Fill dirt around the foundation settles and directs rainwater right to the foundation.

As the run-off seeps through the soft topsoil around the house, it pushes against the walls and stops at the undisturbed ground just beneath the footings. Footing drains may break as the house settles, or silt up. If the soil is clay, water then starts rising in the disturbed soil around the foundation like inside a pool.

Hydrostatic Pressure – When water accumulates around the foundation, hydrostatic pressure builds up and causes the basement to leak. Clay-rich soils do not drain well and hold rainwater right against the foundation walls. Water pushes its way inside through any cracks or joints and the pores in concrete. Rising groundwater is sometimes the problem or even an underground spring. Houses settle and underground water flows change. New construction down the street may shift groundwater flows and cause basement leaks in your house.

Settling Cracks – As houses settle, concrete develops stress cracks that leak water. Exterior waterproofing disintegrates or separates due to the "alkali attack." When water migrates towards embedded steel, it rusts, expands and cracks the concrete.

Efflorescence Signifies Water Seepage – Water penetrates the pores in concrete, dissolves alkalis, and enlarges the pores. As concrete ages, it becomes more and more porous. Initially, the seeping water evaporates, leaving on the surface salts and lime. This "white deposit" or efflorescence is a telltale sign of capillary water seepage.

Plastic Barriers Do Not Last – Concrete slabs, although much thinner than basement walls get even less waterproofing protection. The plastic "vapor barrier" soon disintegrates due to the lime in concrete and over time, the layer of gravel ("drainage pad") silts up. Then, the concrete starts pulling in groundwater by capillary action.

Tar membrane foundation coating.

Settling cracks in basement walls.

Why Exterior Waterproofing Does Not Last

Tar Waterproofing Is Brittle – Tar waterproofing membranes has no "give" and cracks eventually develop as the concrete constantly contracts and expands and the house settles. Similarly, tar paper or pargeting (a layer of mortar) on block walls are inelastic and crack.

Concrete is "very strongly alkaline" (pH above 9). Water carries dissolved alkalis to its surface, where they attack any waterproofing coating by saponification ("alkali attack") and even the concrete itself. Alkaline soils in some regions speed up this process and can "eat" away inches of concrete over several years.

All waterproofing coatings gradually break down or separate, even flexible elastomeric liquid membranes. Elastomeric sheet membranes separate as the alkalis attack the primer and taped joints and their service lives are guaranteed for only 5 to 10 years.

In the end, the concrete is on its own. It may continue to do a good job for several years, but water will gradually activate alkalis, leach out the concrete, and enlarge the pores. Thus making water seepage inevitable! Water is the root problem and only in perfectly dry conditions, would concrete and waterproofing coatings last forever.

Wouldn't it be great to somehow block water migration through the pores of concrete and to neutralize the alkalis in concrete to protect the waterproofing coating against "alkali attack"?

That's exactly what RadonSeal Concrete Sealer does!

How To Waterproof Your Basement in 4-Steps

Tackling a basement waterproofing project can be a daunting task, but the labor involved may not be as strenuous as you thought. Follow this basic step-by-step approach for drying out your damp basement.

Step 1 – Remove any paints, sealers, tile adhesive, efflorescence, and oils from the concrete.

Step 2 – Shop-vac the surface of the concrete removing loose or crumbling concrete, mortar, dust, and dirt.

Step 3 – Seal the concrete walls and floor against moisture and water vapor with RadonSeal Concrete Sealer. You can move all your contents to one side of the basement and seal the other side first. Let the concrete dry then seal the other side.

Step 4 – Make repairs to water leaks through foundation settling cracks, basement floor cracks, cold-joints, control joints, floor-to-wall joints (cove-joint), pipe-protrusions, wire tie leaks, etc.

How To Seal a Stone Foundation Wall – Applying RadonSeal will help strengthen and waterproof old mortar as well as limestone. If needed, remove loose and crumbling mortar, efflorescence and seal the wall using RadonSeal Plus. Afterwards, tuck point holes, cracks and seams in the mortar joints. RadonSeal will not inhibit the bond of new mortar, adhesive, thin set, paints, tiles, and our line of crack and joint repair products.

How To Seal a Brick Foundation Wall – Although it can be used on brick, RadonSeal Concrete Sealer is best used on high-quality concrete. When applying RadonSeal to brick there is a risk of changing the appearance of the brick (leaving a white film on the surface that would be difficult to remove). For waterproofing a brick foundation wall, we recommend sealing it with LastiSeal Brick & Concrete Sealer.


Commercial-Grade Concrete and Basement Care Products

If your basement is still unfinished and unpainted, our line of waterproofing products will make waterproofing your basement concrete quick, easy and saving you on both time and money.

RadonSeal Basement Concrete Sealer – Our champion concrete sealer! RadonSeal works deep inside concrete walls, floors, and heavyweight concrete blocks to help strengthen and waterproofing the substrate permanently. RadonSeal is a water-based sealer that dries clear, leaves no color or film on the surface that can peel off or wear away and cannot be pushed out regardless of hydrostatic water pressure. The cured mineral becomes integral to the concrete. RadonSeal is safe to use indoors because it contains no chemical solvents or VOCs. It's spray-on application is quick and easy for both contractors or homeowners.

The application of RadonSeal is simple! All you will need to apply the product with is a hand-pump "garden or bug" sprayer (readily found in major hardware stores) and a push broom. Review RadonSeal Application Instructions.


DIY Foundation Crack Repair Kits – Our diverse line of foundation crack repairs kits are used for permanently filling cracks in poured concrete walls and stopping leaky cracks. Used by professional waterproofing contractors the low-pressure injection method eliminates any need for drilling making repairs easy enough for homeowners to do themselves. The low viscosity urethane is suitable even for the repair of hairline cracks. The kits arrive to you complete, all you need is a standard caulking gun for injection.

CrackWeld Floor Crack Repair Kits – CrackWeld provides a permanent repair of stress cracks in basement floors and concrete slabs. CrackWeld's low viscosity, self-leveling resin, can penetrate even inside hairline cracks without the need to rout or chase the crack! Designed with flooring contractors in mind, CrackWeld DIY Kits provide a permanent, strong, quick and easy fix for homeowners repairing slab cracks themselves. Each kit ships complete and all you need is a standard caulking gun to use the product.

ElastiPoxy Joint & Crack Filler Kit – ElastiPoxy is a unique product for the repair of control joints, floor-to-wall joints, cracks in concrete blocks and mortar joints, wide cracks in concrete, brick, and masonry (greater than 1/2"). When mixed and used straight (50/50 mixture) ElastiPoxy offers the desired flexibility, bond, and strength needed to make proper repairs of expansion control and floor-to-wall joints. When mixed with construction sand, it will provide a rigid repair. Making it the proper product for repairing cracks in concrete blocks walls, wide stress cracks in floors, mortar joints, and filling concrete spalls in slabs.

How Water Gets Through Concrete

Concrete is naturally porous, typically 10 to 18% air (with extremes 2–60%). To make new concrete "workable," a water-to-cement ratio of 0.45–0.50 is the norm, but cement only needs a half of the water (0.25 w/c ratio) for hydration. As concrete cures, all the surplus water escapes to its surface and evaporates. This "bleeding water" leaves a network of tiny capillaries (pores) inside the concrete.

We cannot see the pores of concrete. Their size ranges from 3 nm (millionths of an mm) to 0.1 mm (the diameter of a human hair). The median is about 1 micron (1,000 nm) but a water molecule is 3,000 times smaller (0.28 nm). By all logic, concrete should leak like a sieve!

So what holds the water back? Not the concrete but the physics of water itself. Although water not as viscous as molasses, it takes pressure to push it through a dry microscopic pore. Surface tension holds the "blob" of water inside the dry pore until its surface gets wet. But add repeated water pressure during occasional rainstorms or condensation on the interior and after a while, the inside of the pore gets wet and water starts flowing through it.

Concrete is hygroscopic. Concrete attracts water by absorption and once the pores wet, they draw up water from the ground below by wicking action (capillary suction). While it may take years for water to start seeping through concrete, nothing holds back soil gases. Invisible water vapor and radon gas can flow freely through the pores and capillaries of concrete. More on Basement Damp-Proofing.

How to Check for Moisture Transmission

Many home sales get re-negotiated or even canceled when the building inspector discovers moisture in the basement. Make sure to check for leaks and any visible cracks in the concrete, the floor-to-wall joints, expansion control joints in the floor, and all penetrations.

You can test for moisture transmission through the concrete by placing a foot-square of plastic or aluminum foil on the floor or wall, seal the edges with duct tape, and check after a couple of days for drops of water. Alternatively, you can use professional Vapor Transmission Test Kits.

What will building inspectors look for?

  • Dampness – Residual dampness at the base of walls.
  • Rust Stains – Signs of rust at the base of steel posts or the heater. Discoloration or decay on wood partitions, paneling, drywall, wood posts.
  • Efflorescence – Signs of "white powder" deposits on the concrete walls and floor.
  • Peeling – Peeling floor tiles, paint, or mildewed carpeting.
  • Mildew & Mold Stains – Stain from mildew on objects stored on the floor.
  • Dampness – Dank odors in carpeting and finishes
  • Musty Odors – A musty smell indicates that molds or mildew have already taken hold.
  • Condensation – On windows and concrete surfaces.
  • Rain Gutters – Plugged or damaged rain gutters.
  • Grading – Improper grading, puddling of water, saturated zones, and the growth of moss.

Waterproofing New Concrete Foundations

RadonSeal Concrete Sealer preserves new concrete and it protects concrete against the gradual deterioration caused by groundwater. Sealing the concrete early on, particularly before finishing the basement, will help avoid future headaches! If you have a brand new basement, now is the best time to prevent future moisture problems, to waterproof and strengthen the concrete, reduce cracking, efflorescence ("white powder"), dusting and to preserve the concrete.

As concrete cures, it inevitably develops capillaries. Allow new concrete to cure for at least 28 days before sealing and damp-proofing the poured walls and slab with RadonSeal Standard. In case of concrete block or cinder block walls, allow new mortar to cure for at least 14 days before applying RadonSeal Plus and Ion-Bond Armor.

Waterproofing Foundations on The Exterior

Combining RadonSeal With An Exterior Waterproofing Coating – RadonSeal is commonly used in combination with exterior foundation coatings (damp proofing membranes), which are required by building codes in most counties. One of the benefits RadonSeal provides to concrete (prior to applying a coating), is the ability to neutralize alkalis in concrete. Neutralizing the alkali will help extend the life of waterproofing membranes, paints, tar, rubberized sealants, against alkali attack.

Exterior coatings waterproof concrete by encapsulation and seal water leaks by bridging settling cracks, cold pour joints, protrusions, seams, holes, and minor defects. RadonSeal plays it's part in the damp proofing process by restricting the movement of water through the capillaries of concrete. It is the line of defense that the concrete foundation will benefit from when exterior membranes begin to deteriorate, crack, and release.

The lower the quality of concrete, the higher the need to apply RadonSeal before a waterproofing coating. Foundation walls constructed of cinder blocks or heavyweight concrete blocks, have thin walls (1-1/4" thick) on both sides of the hollow cores. Cinder blocks that leak routinely, can have large visible pores making it much more difficult to seal. The most effective method for waterproofing a newly constructed basement wall, is to seal both sides of the concrete with RadonSeal. Afterwards, allow the sealer to initially cure and for the concrete dry before applying the exterior waterproofing coating (2-4 days).

Taking into consideration aggresive timelines, when contractors are required to backfill sooner, install the exterior waterproofing coating and apply RadonSeal to the interior basement walls.

Alternative Waterproofing Methods for Basements

Install a Sump Pump ($900–$1,500) – If your water issue is serious (a high water table), you will need to purchase and install a sump pump. Sump pumps drain water from the gravel bed underneath the basement floor. Relying on one sump pump, however, is risky, particularly if your basement is finished! The pump or the grid may fail during a severe storm or spring snow melt. Installing a backup, either a battery-powered backup sump pump or a water-powered backup sump pump is a smart decision and inexpensive insurance.

Interior Drainage Gutters ($3,000–$6,000) – A plastic channel system ("interior gutters") is glued around the perimeter of the basement floor to collect water seeping through the foundation walls and to take it to a sump pump basin. Why is installing plastic channels a bad idea? If you are planning to remodel your basement, common sense would tell you that water should be kept out and not allowed to seep in. It would be impossible to frame and finish the walls because water sitting in the channels behind the drywall would lead to mold and mildew problems. Moreover, the channel system does not address water seeping directly through the concrete floor.

Exterior Footing Drains ($13,000–$20,000) – Excavating earth next to the foundation walls, laying gravel, installing perimeter drains, removing old tar from foundation walls, sealing the concrete, applying a polymer waterproofing membrane, backfilling, and finally, re-landscaping.

Interior French Drain ($5,000–$9,000) – The "go-to" solution of most waterproofing contractors. To install the French drain, the perimeter of the basement slab must be jack hammered. Dirt will then be dug out to form a trench, followed by laying a perforated pipe over a stone bed. The pipe will drain the water from underneath the basement floor to a sump basin. The trench is then filled back in with concrete. This method does not work very well if the gravel bed is silted up and does little for seepage through basement walls. For foundation walls constructed of cinder blocks, contractors will sometimes leave a gap between the floor-to-wall joint. This allows water, seeping through cracks, mortar joints and the blocks themselves, to flow down and into the French drain. These open gaps, and the natural vacuum in basements, can cause the inflow of moisture-laden gas and radon gas from the soil. This can increase humidity and harmful radon gas levels in the basement.

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