Photograph of polyurethane foam being injected into a concrete foundation crack How to Repair Foundation Cracks Using Polyurethane Foam Injection

  • POLYURETHANE FOAM INJECTION - CONTENTS: How to make a foundation crack repaior leakage seal using polyurethane foam. How to Stop Basement or Crawl Space Water Leakage Through Cracks. Guide to sealing foundation cracks using injectable foam. Foundation crack repair products, materials, where-to-buy sources, alternatives. List of Polyurethane Crack Sealants Products, Sources, Brands, Manufacturers
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Foundation wall or slab crack repair using polyurethane foam injection: this article explains how to use injected polyurethane foam to repair a concrete basement (or crawl area) wall or slab crack in order to stop basement or crawl space water entry or air leakage.

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How to Repair a Leaking Basement Foundation Crack by Polyurethane Foam Injection

Photograph of polyurethane foam being injected into a concrete foundation crack Aaron Kuertz, Applied Technologies

A variety of site conditions can lead to cracks in a concrete or other masonry foundation wall. Speaking generally, foundations may be damaged and cracks may appear from innocent causes unlikely to affect the structure such as shrinkage cracks, initial settlement, or from potentially more serious causes such as ongoing settlement, unusual pressures or loading, or from improper construction.

Before repairing a foundation crack by sealing it against water entry, it is important to diagnose the cause of the crack and its effects on the building structure. If there is an underlying ongoing problem causing foundation movement or damage, that problem should be corrected.

Cracks in concrete walls that are larger than 1/4", cracks which are increasing in size, or cracks which are indicative of foundation movement should be evaluated by a professional. The diagnosis and evaluation of foundation cracks and structural foundation damage and repair methods are discussed at FOUNDATION REPAIR METHODS

Shrinkage cracks and in some cases other foundation cracks such as those caused by minor initial settlement might not be a structural concern but may still form an opening leading to water leaks into the building. Concrete shrinks as a natural process of it curing. This shrinkage causes the concrete to develop stresses and to relieve it, the basement wall cracks.

Photograph of a classic shrinkage crack in poured concrete wall.

Concrete shrinkage cracks are a common condition in a concrete foundation [or also in concrete slabs unless control joints were used in the wall or floor design] and occur when concrete shrinks as it dries and cures.

Shrinkage cracks are easy to recognize and to distinguish from cracks that occur later in the life of a foundation because [usually] the cracks are not continuous and tend to extend in a very irregular line through the concrete (as shown in the photo) range in length from a few inches to the entire height of the concrete wall, extending from wall top to bottom.

Concrete shrinkage cracks virtually always extend through the full thickness of the foundation wall, which means they can provide a ready path for water entry into the building.

Common areas for a shrinkage concrete crack to develop are under a basement window, above a doorway in the middle of a long wall or where the foundation "steps down." Shrinkage cracks also often occur near the middle of a large poured concrete wall [or floor] if no control joints were used. [Concrete control joints are very often omitted in residential construction. Shrinkage cracks and how to recognize and diagnose them are discussed further at SHRINKAGE vs EXPANSION vs SETTLEMENT.

Once concrete cracks in a basement or crawl space wall or floor slab, it is possible for water to leak into a building through the crack. There are several ways to repair a basement crack leak. An easy, quick, and effective measure to stop basement or crawl space water entry through a foundation crack is to perform an injection of polyurethane foam into the basement crack. [Also be sure to find and fix the sources of water outside.]

Photograph of polyurethane foam foundation crack repair kit

Both commercial and home-owner "do it yourself" kits and equipment are available to seal foundation cracks using this foam method. [Photograph of this foundation crack repair kit, courtesy of Applied Technologies].

Polyurethane foams are injected into the basement crack in a liquid form. This allows a gentle and slow filling process of the basement crack that will completely fill the crack. After a few minutes the polyurethane will begin to react with the water in the crack to begin foaming. Water is actually the catalyst that converts the liquid polyurethane into foam. This foaming action increases the volume of the polyurethane up to 30 times its liquid form.

As the polyurethane foam expands it fills the basement crack from bottom to top and front to back. The finished foam will be a closed cell structure that will not allow water to leak into the basement crack. In fact, if there are any voids in the soil outside of the basement- such as under a rock or if the foundation is backfilled with gravel-the polyurethane foam will expand and extend out into the void.

The polyurethane foam forms a strong bond to the concrete. This bond will be able to withstand the hydrostatic pressure that may develop from high subsurface water levels. High underground or "subsurface" water levels are typically caused by heavy rains and most-often by failure to direct roof runoff or nearby surface runoff away from the building.

This concrete crack repair process using polyurethane injection is likely to be more successful and more durable than other crack patching methods. Surface patching of the crack is just that. Only the inside of the basement wall is covered by a repair. Chiseling out the crack and filling it with hydraulic cement only fills a portion of the crack.

Water can still enter the basement crack and will eventually force out the patch or hydraulic cement. [Forces that tend to cause separation of poorly-bonded concrete surface patches include the molecular action of crystallizing mineral salts left behind as moisture passes through the masonry wall.]

Basement crack injection is a quick repair process that stops water leaks. The technician does not have to drill into the concrete to do it. For this reason the basement crack repair is a clean process. The technician will attach ports to the surface of the basement crack that allow the liquid polyurethane to enter the basement wall and stop the leak.

Once the basement wall crack is completed, water will not be able to leak into the basement. Now the homeowner's possessions will be safe. As will any insulation on the basement walls, the drywall or the framing used to finish the basement.

List of Polyurethane Crack Sealants Products, Sources, Brands, Manufacturers

  • Applied Technologies polyurethane crack sealant: the foam sealant discussed in the article above as well as other foundation crack repair products are available from Applied Technologies and include a polyurethane foam used to seal leaky basement cracks (this is not a structural repair it's a waterproofing measure).

    The company sells other foundation repair products (dowel rod epoxy) as well as foundation and basement waterproofing, drainage, and damp proofing products as well. 1-877-277-5948, 513-939-3767 or Fax: (513) 939-3787. Website:
  • Crack-Pac® Flex-H2O™ Polyurethane Crack Sealer, suitable for sealing cracks from 1/32" to 1/4" in width in concrete and solid masonry.

    Quoting: Crack-Pac® Flex-H2O™ is a high solids hydrophobic polyurethane injection resin designed to seal leaking cracks, voids or fractures in concrete or solid masonry. The polyurethane is packaged in the cartridge and an accelerator is packaged in the nozzle. When the two are combined in the cartridge and mixed, the result is a low viscosity, water activated polyurethane. When the resin encounters water as it is injected into the crack, it becomes an expanding foam that provides a flexible seal in leaking and non-leaking cracks.

    This product is produced and sold by Simpson StrongTie. Simpson Strong-Tie Company, Inc.,
    5956 W. Las Positas Blvd. Pleasanton, CA 94588. Website:
  • Quickcrete 862018 10-oz Polyurethane Mortar Crack Sealant, Tel: 1-800-282-5828, Website:,

    Quoting: Mortar repair polyurethane, commercial grade interior/exterior Size Oz=10 Color=Gray High performance, construction grade sealant waterproofs, seals and tuck-points damaged mortar joints. Textured one-component, fast-curing, flexible material providing a durable elastic bond. Adheres to concrete, masonry, stucco, pre-painted metal, glass,plywood, aluminum, steel and many plastics and composites. Can be applied to approximately 12 lineal feet in a 3/8" bead.
  • QUIKRETE® Polyurethane Concrete Crack Sealant (No. 8620-17) is a high performance, construction grade polyurethane sealant permanently seals and waterproofs cracks in concrete, masonry and stucco surfaces. Contact information shown just above.
  • Loctite® PL® S10 Polyurethane concrete crack & masonry sealant, Loctite Corporation, Loctite® Brand - Consumer Products Henkel Corporation 26235 First Street Westlake Ohio 44145, Tel: 800-624-7767.

    Quoting: Loctite® PL® S10 Polyurethane Concrete Crack & Masonry Sealant is a premium quality, commercial grade sealant developed especially for forming permanent, water and weatherproof seals in all exterior gaps and joints. This sealant is elastic and remains flexible to expand and contract with construction material movement to protect and retain the original seal. Loctite® PL® S10 Polyurethane Concrete Crack & Masonry does not require a primer for concrete, brick, stone or masonry and resists deterioration from weather, stress or movement.
  • Loctite® PL® S20 Polyurethane self-leveling concrete crack sealant, Loctite Corporation, Loctite® Brand - Consumer Products Henkel Corporation 26235 First Street Westlake Ohio 44145, Tel: 800-624-7767.

    Quoting: Loctite® PL® S20 Polyurethane Self-Leveling Concrete Crack Sealant is a professional grade sealant for concrete. It is a one component, polyurethane, self-leveling sealant for contraction / expansion joints and cracks in concrete floors and decks. It cures in place to form a highly resilient and abrasion resistant seal, which resists deterioration caused by weather, stress, movement, traffic and water. Its abrasion and tear resistance makes it ideally suited for applications exposed to pedestrian and vehicular traffic.
  • Mar-Flex Polyurethane Concrete Crack Repair Kit, Tel: 800-498-1411, Website:

    Quoting: Low-pressure injection and repair of approximately 8-10 lineal feet. Contains the following; (1 jar 8oz.) Mar-flex Crack Seal (1 jar 8oz.) Port Adhesive (2) Wooden Sticks (12) Surface Ports and Caps (2 Cartridges) Mar-flex Injection Polyurethane/Epoxy Resin 1:1 (2) 3/8" :24 Mixing Nozzles (1) Injection Hose Assembly with plastic shut-off valve (2 pair) Latex Gloves (1) Plastic Trowel (1) Wire Brush (1) Drop Cloth (1) Complete Instructional DVD. The company also offers low-viscosity creack filler that can be injected into both dry and damp cracks and a "Seal & Peel" crack repair kit.
  • RadonSeal D-I-Y two-component polyurethane or epoxy crack repair kits. Radon Mitigation & Concrete Waterproofing Co., Novion Inc., 18 L'Hermitage Drive, Shelton, CT 06484 USA. Website:,

    Quoting: Each D-I-Y kit is able to repair up to 10 linear feet of cracks in poured concrete walls from hairline to 1/2" wide. You can choose to inject either expanding polyurethane or epoxy. Since most cracks are non-structural, we use polyurethane on almost all cracks because it works inside wet cracks.

    You also have the choice of the standard epoxy surface sealer when the wall will be framed in or if appearance matters, the Easy-Peel surface sealer which can be easily removed after the repair. If you have more than 20 linear feet of cracks, it is more economical to purchase our Professional Foundation Crack Repair Toolkit. These kits include a professional caulking gun, which makes the job even easier. If it is a smaller project, like filling the voids around pipes or leaking form ties, use our PipeTite Gap Filler Kit.


Continue reading at SEAL CONCRETE CRACKS, HOW TO or select a topic from the More Reading links shown below.

Or see FOUNDATION REPAIR METHODS for a more extensive discussion of types of foundation damage and how it is repaired. [Photograph of this foundation crack repair process using foam injection, courtesy of Applied Technologies]


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POLYURETHANE FOAM INJECTION at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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