Basement Wall Crack Repair Made Easy: A DIY Guide

Don’t Let Basement Wall Cracks Lead to Bigger Problems

Noticed a crack in your basement wall? Don’t ignore it—what seems like a minor issue today can quickly lead to water intrusion, mold growth, radon gas infiltration, or even structural damage.

The good news? Most basement wall crack repair projects can be handled by homeowners without hiring a contractor. With the right tools and a bit of know-how, repairing foundation cracks becomes a manageable DIY task that saves both time and money.

For over 25 years, RadonSeal has helped thousands of homeowners perform professional-grade basement wall crack repair using easy-to-use, all-in-one kits. Whether you’re stopping water leaks, blocking radon, or prepping your basement for finishing, we’ve got a DIY solution that works like the pros—without the cost.

Why Basement Wall Cracks Happen

Cracks in basement walls—whether poured concrete or concrete block—are more common than you might think. While some cracks are harmless hairline fractures, others signal underlying issues like soil pressure, poor drainage, or settling.

Here are the most common causes of foundation wall cracks:

• Shrinkage during curing – Too much water or rapid drying can create small cracks as the concrete hardens.

• Expansive clay soils – These soils swell and shrink with moisture changes, pushing against the foundation.

• Hydrostatic pressure – Waterlogged soil puts force on the wall, especially after heavy rains.

• Improper backfilling or poor compaction – Can lead to uneven settling and foundation stress.

• Freeze-thaw cycles – Repeated expansion and contraction of soil stresses the wall over time.

• Gutter and drainage issues – Water pooling near the foundation increases pressure and risk of cracks.

Regardless of the cause, basement wall cracks can allow water, radon gas, moisture, and even pests into your home. That’s why early basement wall crack repair is key to protecting your foundation and air quality.

Types of Basement Wall Cracks (And What They Mean)

Identifying the direction and pattern of a basement wall crack is crucial—it helps determine whether the crack is cosmetic, waterproofing-related, or a sign of structural damage. Here’s how to tell the difference:

🔹 Vertical and Diagonal Cracks

These are the most common cracks found in poured concrete foundation walls. They often occur within the first month after construction due to concrete shrinkage or minor foundation settling.

Where they appear:

• Near basement window corners

• Along cold joints or form seams

• Around utility penetrations and tie rods

What they mean:

• Typically non-structural

• Can leak water, soil gases, and humidity

• May widen slightly over time with continued settling

• Ideal candidates for low-pressure polyurethane injection to permanently seal against leaks

💡 Tip: Even hairline cracks can allow water seepage or radon infiltration—don’t ignore them.

🔹 Horizontal Cracks

A horizontal crack in a basement wall—especially through the midsection—can signal serious trouble. These cracks are often caused by hydrostatic pressure or expansive clay soils exerting force on the wall from the outside.

Warning signs:

• Crack is wider than 1/4 inch

• Wall shows signs of bowing or inward deflection

• Crack spans the full width of the wall

What they may indicate:

• Structural risk to the wall’s integrity

• May require professional stabilization, such as carbon fiber straps or wall anchors

• Should not be ignored or patched without a full assessment

⚠️ Structural cracks often worsen over time. Monitor them for changes and consult a foundation specialist if in doubt.

How to Fix Basement Wall Cracks on Your Own

Most minor basement wall cracks—especially if they’re dry, narrow, and not actively moving—can be permanently repaired from the inside without expensive excavation or hiring a contractor. Thanks to modern crack injection systems, DIY basement crack repair is more effective and accessible than ever.

🔧 Polyurethane Crack Injection (For Poured Concrete Walls)

For vertical or diagonal cracks in poured concrete foundation walls, low-pressure polyurethane injection is the preferred repair method. The liquid polyurethane expands inside the crack to form a flexible, closed-cell foam that fills the entire depth of the wall.

Benefits:

• Permanently waterproofs the crack

• Expands and seals against future movement

• Stops radon gas, moisture, and soil air infiltration

• Bonds tightly to concrete—even if slightly damp

🔨 Best for: Hairline to wide cracks in poured concrete basement walls

💡 Tip: Use a complete DIY crack injection kit like the RadonSeal® Foundation Crack Repair Kit for a professional-grade seal.

🧱 Crack Repair in Concrete Block Walls (CMU Blocks)

Unlike poured concrete, hollow-core block walls can’t be injected with foam because the sealant leaks into the open cores. Instead, cracks must be routed out with a grinder and filled with a semi-rigid epoxy paste like ElastiPoxy® Joint & Crack Filler.

How it works:

• Mix ElastiPoxy with dry sand to form a paste

• Trowel into the routed crack for a permanent seal

• Bonds to both block faces and mortar joints

• Remains flexible—won’t crack or peel with wall movement

🔨 Best for:

• Step cracks in block walls

• Mortar joint cracks

• Through-block cracks where cores are not open

💡 Bonus: ElastiPoxy can also be used to fill control joints or wider cracks in concrete floors and walls.

DIY Foundation Crack Repair Kits vs. Hiring a Pro

Not every basement crack requires a contractor. In fact, most non-structural cracks—especially those under 1/4 inch wide—can be sealed permanently by homeowners using a foundation crack repair kit.

✅ When DIY Repair Makes Sense

• The crack is vertical, diagonal, or even horizontal but not actively bowing

• It’s in poured concrete, not block

• There’s no significant wall movement

• You want to stop water seepage, radon entry, or prevent further deterioration

RadonSeal offers both flexible polyurethane injection kits for waterproofing and structural epoxy injection kits for reinforcing load-bearing cracks. Our kits are designed for homeowners and include professional-grade materials and detailed instructions.

With a little prep and patience, most repairs can be completed in under two hours—no special tools or experience required.

👷 When to Call a Professional

Some cracks indicate more serious structural concerns and may require expert evaluation. You should consider hiring a foundation repair contractor if:

• The wall shows signs of bowing, displacement, or movement

• The crack is in a block foundation and involves widespread damage

• The repair involves multiple cracks or structural stabilization

In these cases, professionals may use wall anchors, piering, or a foundation rebuilt to restore the integrity of the structure.

DIY Crack Repair Kits That Work

You don’t need to be a contractor to fix basement wall cracks—just the right tools, materials, and a little guidance. RadonSeal’s complete DIY crack repair kits are designed to make basement wall and floor repairs fast, permanent, and hassle-free—even for first-time homeowners.

Each kit includes everything you need for a successful repair:

• Injection foam or structural epoxy

• Injection ports and surface sealing paste

• Mixing tools, caulk gun, and step-by-step instructions

🧰 Choose the right kit for your project:

• CrackWeld Floor Repair Kit – for hairline or structural cracks in basement floors

• RadonSeal DIY Urethane Crack Injection Kit – for vertical or diagonal cracks in poured concrete walls

• RadonSeal® DIY Epoxy Crack Injection Kit – for horizontal or structural cracks that require added strength

• ElastiPoxy Crack Filler – for floor-to-wall joints, cove joints, and step cracks and mortar joints in block walls

Final Thoughts: Fix Basement Wall Cracks Before They Get Worse

Basement wall cracks are more than just cosmetic—they’re direct pathways for water intrusion, radon gas, humidity, and even pests. Left untreated, they can lead to mold, structural deterioration, and costly repairs down the road.

The good news? Most wall cracks can be fixed permanently with a DIY injection kit. Whether you’re sealing a hairline crack or reinforcing a larger horizontal crack, RadonSeal has a proven solution designed for homeowners.

✅ Why Choose RadonSeal Repair Kits?

• Professional-grade materials—no contractor required

• Polyurethane and epoxy options for waterproofing and structural strength

• Kits tailored to poured concrete or block walls

• Backed by 25+ years of field-proven performance

🔗 Ready to fix that crack for good?
Explore our Crack Repair Guide or Contact Us for help choosing the right solution.