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How to Seal Cracks in Concrete Floors & Walls StructAPedia © Enter your search terms Submit search form   Search This Website - InspectAPedia.com

• Recommended methods for sealing cracks in concrete floors & slabs
• Concrete expansion joint sealant products, expoxies, caulks
• When should we not seal a foundation wall or floor slab crack?

This article how to seal and repair of cracks in poured concrete slabs, floors, or walls. Also see How to Repair Foundation Cracks Using Polyurethane Foam Injection which explains how to use this special method for sealing non-structural cracks in masonry walls or floors, and see FOUNDATION REPAIR METHODS for a more extensive discussion of types of foundation damage and how it is repaired.

This website describes how to recognize and diagnose various types of foundation failure or damage, such as foundation cracks, masonry foundation crack patterns, and moving, leaning, bulging, or bowing building foundation walls.

Types of foundation cracks, crack patterns, differences in the meaning of cracks in different foundation materials, site conditions, building history, and other evidence of building movement and damage are described to assist in recognizing foundation defects and to help the inspector separate cosmetic or low-risk conditions from those likely to be important and potentially costly to repair. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

How to seal control joint & expansion joint cracks in concrete slabs

Warning: some crack sealing operations may make crack diagnosis or monitoring more difficult First of all do not just seal a crack if the crack size, shape, pattern, location, or other evidence indicate that something important is going on with the foundation. If for example we think that there may be active foundation movement or settlement going on and if that condition is going to be monitored for evidence of further movement, just pushing a flexible sealant or caulk into a crack is leaves some worries unattended:

• Using a flexible sealant in a structural crack may make it difficult to see small amounts of future movement since the sealant may stretch and tolerate small increases in crack width. This can increase the difficulty of crack monitoring and diagnosis
• Using a sealant in a foundation or floor slab crack may fail to address the underlying cause of the problem such as foundation settlement or frost heaving which need to be addressed
• Using a sealant in a crack, except for some structural epoxies, may seal but not "repair" the damage in any structural sense

We may decide to seal a cracked wall or floor slab anyway, to try to reduce water entry in a building, but remember the implications of sealing we've just listed.

How to seal a cracked masonry foundation wall or floor slab

To seal a shrinkage crack or a control joint crack in a poured concrete slab, regardless of whether or not it has occurred at an expansion or control joint, it may be appropriate to seal the surface to resist water entry and radon gas entry. Control joints are also sealed to provide a smooth and clean concrete surface which does not collect surface moisture or debris. Keeping surface water from entering at a control joint might in some cases also help avoid uneven soil settlement below the slab and tipped or heaved slab sections.

To seal a control joint or expansion joint crack in a concrete slab use a flexible sealant designed for foundation crack repair or sealing. The radon mitigation industry offers special foundation caulks and sealants for that purpose as well. (If water is coming up through a concrete floor or slab, sealing cracks is probably not going to be enough - you need to address the cause of water below the floor.)

List of materials used to fill poured concrete slab control joints include:

• Pre-fabricated control joint strips of plastic or other material
• Masonry caulks or radon sealant caulks
• Semi rigid epoxy resin crack fillers intended for concrete expansion joints such as
  • Shor D 65-80®
  • Elasta Gel 6170 Epoxy® flexible epoxy and expansion joint sealant, two component, no VOC, flexible expoy resin which is rated for use on parking decks and, according to the manufacturer, Lone Star Epoxies, can also be used to repair concrete spalling on such surfaces.
  • other semi-rigid, epoxy products
• Special polyurea caulks designed as a joint filler

Any sealant that is going to be used to fill a control joint in a slab needs to have the ability to bond to the sides of the cut or opening of the joint, to remain flexible over temperature and moisture changes, and to withstand both compression and expansion as the concrete moves in response to curing and in response to temperature and moisture changes.

Epoxy, for example, is not generally used to fill the expansion joint in newly-poured concrete because the concrete is just too wet and has too much movement for the epoxy to bond and perform acceptably. Similarly, a special product would be needed to fill a control joint in concrete in very cold weather.

Typical concrete crack preparation for sealant with an expoxy product

1. Cleaning a concrete crack for patching and sealing: The crack or expansion joint must be cleaned of all debris; power washing and vacuuming may work but inspect the crack or joint to be sure it is clean along its entire length. Otherwise the sealant may fail to adhere and the crack will leak. Wire-brushing or chipping the crack sides is not normally required when using an epoxy sealant. (Traditional concrete or masonry patching (and plaster repairs), on the other hand, was traditionally applied after cracks were chipped and widened into an inverted "vee" shape to help keep the patch material in the crack.)
2. Mix the epoxy sealant according to the manufacturer's directions. Some low volume expoxy sealants are supplied in a dispenser which mixes the two parts together in the proper ratio automatically during dispensing from a tube (see your dentist for an example.) Other crack sealants such as prepared caulks, may come pre-mixed in a tube.
3. Install the backer rod specified by the sealer manufacturer if you are sealing an expansion joint. Sand (clean, dry) may be used as a filler for cracks - an easier approach if you are repairing an irregular crack in a floor. Sand should stop about 3/4" from the top of the floor surface to give adequate volume of sealer epoxy in the crack. The backer rod provides a flexible filler that keeps the sealant in the joint during curing and also reduces the total volume of concrete crack sealer epoxy needed. We recommend using backer rods also if sealing wide cracks in concrete walls or floors, but first you need to have those cracks evaluated to determine the cause as other important structural reparis could be needed first.
4. Epoxy crack patch cure time: Keep traffic off of the sealed crack until the sealant has cured. Typically a thin film will form on a crack filler epoxy in 8 hours, the sealant will be hard enough to withstand traffic in 24 hours, and it will fully cure in about a week.

These notes are based on epoxy product application information available from Lone Star Epoxies.

Use of Polyurea as a control joint filler in concrete slabs

Polyurea joint filler products for concrete control joints have received attention for filling concrete control joints and is increasingly used in that application since this material is resistant to moisture, has high adhesion properties when used with concrete, and will cure in very cold weather. Polyurea sealant products are also reported to be useful in sealing control joints in "green" concrete which has not yet had its full 28 day period of initial curing.

See Polyurethane Foam Injection for details of the procedure for using polyurethane foam to seal foundation cracks.

Use of Epoxy-supported Grouts as a control joint or crack filler in concrete slabs or walls

Epoxy grouts are available which can be mixed and trowelled into a concrete crack or joint. These products are less flexible than the control joint fillers described above. In our opinion, an expoxy grout filler may work fine to provide a well-bonded repair to a stable wall or floor crack in an area where there is no anticipated further movement such as from temperature or moisture variations. But read the manufacturer's intended application before buying an expoxy reinforced grout for building crack repair. Do not use the product where it was not intended unless a call to the manufacturer provides you with good information that it's acceptable to do so.

On the one hand we like using a rigid material to fix a supposedly stable crack in a residential building since the fact that the patch is inelastic means it will be easy to see if there is ongoing or new building movement.

On the other hand, a small amount of movment in a foundation wall or floor slab due to changes in temperature will leave a flexible crack filler un-damaged and sealed where a rigid material may fail.

Epoxy Grout Product examples include

• Ramset™ Epoxy Grout - a pourable expoxy resin, also can be mixed with sand and applied with trowel.
• Epoxy grouts (ANSI 118.3 1988) for tile applications (watch out for proper tile surface cleaning within the cure time; cleanup is done using water)
• Laticrete™ epoxy grouts

List of the Types of Tile Grouts, their Bonding Agents and other Properties

• Portland cement grout (ANSI 108.10 1985)
• Latex-modified portland cement grouts (we've used these with good success indoors in tile floors for better water resistance)
• Epoxy grouts (described above) usually with a water-dissolved mix
• Modified Exoxy grouts (ANSI 118.8 1988.) combining portland cement and expoxy (some sources say the chemical resistance is similar to straight Portland cement but the result is a harder grout - just what chemicals are resisted may vary among products)
• Furan resin grouts use furfuryl alcohol in their prodcuts - no water is used. These are highly acid-resistant, also difficult to install.

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Repair of Foundation Cracks

For detailed information about foundation repair methods, including repairs to various kinds of cracks in concrete, see:

• How to Seal Cracks in Concrete - you are currently on this web page.
• Shrinkage Crack Repairs
• Polyurethane Foam Injection for details of the procedure for using polyurethane foam to seal foundation cracks.
• Cracks at Control Joints in Concrete how we prevent shrinkage cracks in poured concrerte floors and walls
• FOUNDATION REPAIR METHODS for our catalog of Foundation Repair Methods - Examples of Typical Foundation Repairs for various types of foundation cracks, leaks, settlement, movement, or other failures

FOUNDATION DIAGNOSIS Chapter Index

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Technical Reviewers & References

Particular thanks are due to experts and also consumers who read these articles and suggest corrections, changes, and additions to the material. Content suggestions, technical corrections and content critique are invited for any of the content at our website.

• Daniel Friedman - principal author/editor of the InspectAPedia ^TM Website
• "Best Practices for Concrete Sidewalk Construction," Balvant rajani, Canadian National Research Council
• "Design Considerations for Perlite Roof Slabs," a chapter in "Perlite Concrete Grade for Lightweight Concrete Construction", United Perlite Corporation
• "Quality Standards for the Professional Remodeling Industry", National Association of Home Builders Remodelers Council, NAHB Research Foundation, 1987. See our books at "Structure" at the InspectAPedia Bookstore
• Lone Star Epoxies, Rowlett TX, product literature, includes application instructions for this flexible expoxy resin concrete expansion joint sealer. ls@lsepoxies.com - 10/06/08
• Ramset™ Epoxy Grout, Australia,
• Laticrete™ Epoxy grouts
• Critique, contributions wanted: Contact Us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

More expert information on this topic

More Information on Building Diagnostic Inspections and Repairs

Repair of Foundation Cracks

For detailed information about foundation repair methods, including repairs to various kinds of cracks in concrete, see:

• Shrinkage Crack Repairs
• Polyurethane Foam Injection for details of the procedure for using polyurethane foam to seal foundation cracks.
• Cracks at Control Joints in Concrete how we prevent shrinkage cracks in poured concrerte floors and walls
• How to Seal Cracks in Concrete
• FOUNDATION REPAIR METHODS for our catalog of Foundation Repair Methods - Examples of Typical Foundation Repairs for various types of foundation cracks, leaks, settlement, movement, or other failures


• SHRINKAGE vs EXPANSION vs SETTLEMENT
• Evidence of Foundation Shrinkage
• Evidence of Foundation Expansion
• Foundation Settlement: crack patterns, other evidence

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