Can I use cement to fill cracks?

Table of Contents

Quick Answer

Yes, cement can be used to fill cracks in concrete, masonry, brickwork, and some natural stone surfaces. Cement is an effective patching material for hairline cracks, small holes, and other minor defects in these materials. Some key things to know when using cement for repairs:

Use a cement-based mortar, not pure cement. Mortar provides adhesion and flexibility.
Make sure the area is clean before applying. Remove loose material and debris.

Dampen the repair area before filling to prevent premature drying.
Fill the crack fully and apply mortar slightly proud of the surface.
Allow proper curing time before exposing repaired area to use.

With proper preparation and application, cement mortar can provide a long-lasting patch in many cases. It bonds well to cured concrete and masonry surfaces. However, cracks may reappear if movement continues in the damaged area. See full article for more details on cement crack repair.

What causes cracks in concrete and masonry?

Cracks can form in concrete, brick, stone, and stucco surfaces due to a variety of factors:

Shrinkage – Concrete and mortar shrink as they cure. This creates internal stresses that can cause cracks.

Settlement – Settlement of the ground beneath causes cracking as the surface drops unevenly.
Freeze-thaw – Water seeping into tiny pores, then expanding as it freezes, stresses the material.
Structural stress – Excessive loads or movement in the structure creates external forces.

Poor construction – Insufficiently thick sections, large coarse aggregates, or poor curing practices make cracking more likely.

Cracks tend to form in predictable patterns based on the cause. Identifying the source of cracking can help prevent future recurrence. Properly repairing existing cracks is key to maintaining surface integrity.

What types of cracks can be filled with cement?

Cement-based mortar works well for repairing the following types of deficiencies in concrete and masonry:

Hairline cracks – Thin cracks less than 1/16 inch wide can be filled with cement patching compound.
Narrow cracks – Cracks up to 1/4 inch wide are candidate for cement mortar repair.
Small holes/divots – Minor voids, chips, and pop-outs can be filled with cement mixtures.

Masonry joints – Deteriorated mortar joints are readily repaired with fresh cement mortar.

Larger cracks, those with ongoing movement or structural issues, may require other methods like epoxy injection or route-and-seal techniques. Always evaluate the proper repair strategy based on the type and extent of damage.

For best results, cement patching should only be used to repair stable cracks and defects in structural sound surfaces. It provides a rigid filler with compressive strength, but limited flexibility.

How to Prepare the Damaged Surface for Cement Repair

Proper preparation is crucial for cement mortar repairs to adhere and perform well:

Use a wire brush, chisel, or grinder to remove all loose material within and around the damaged area. Clean cracks should be exposed.
Chase or cut out cracks wider than 1/4 inch using a masonry blade to create square sides.

Use water or compressed air to wash out any dust or debris immediately before application.
Pre-wet the repair zone with clean water. Concrete should be saturated but without standing water.

Take care to clean the damaged area while avoiding further harm to the surrounding surface. Prepare cracks to an appropriate size and shape to hold the patching compound. Proper cleaning and pre-wetting provides the ideal conditions for the cement to bond.

Mixing Cement Mortar for Patching

For best results, use a premixed cement patching compound or make your own mortar mixture:

Premixed compounds feature graded aggregates and polymers for adhesion and strength.
Mortar can be mixed using one part Portland cement to two or three parts sand. Add latex additive for better flexibility and bonding.

When making your own mortar:

Use clean water and materials. Dirty water or contaminated cement/sand will weaken the mix.
Add materials in the proper proportions. Too little or too much water impacts strength.

Mix thoroughly until uniform consistency is achieved.

Test the mixture for proper viscosity – it should be thick enough to fill cracks but still be workable. Mortar that is too thin will not remain in vertical applications.

Filling Cracks and Voids in Concrete and Masonry

Work the mixed cement product into cracks and defects using these tips:

Apply pressure with a trowel or putty knife to fully pack the material into the damaged area.
Slightly overfill the patch, leaving it proud of the surrounding surface.
Smooth and shape the wet cement to match the form of the repaired zone.

Keep the filled area damp for at least 48-72 hours for proper curing.

On larger repairs, apply cement mortar in layers, allowing each to partially cure before adding more. Cold weather application may require tenting, heating, or insulation blankets to aid curing.

Take care to fully fill all cracks and seal any gaps at edges. A solid repair without voids is critical to achieving strength and longevity. Proper curing conditions must be maintained.

Curing Cement Crack Repairs

Allowing cement mortar patches time to cure properly is vital to achieving strength and durability:

Keep repaired area damp for 3 days using periodic misting or wet burlap.
Avoid loading or disturbing patch for at least 7 days after application.

Protect from freezing, hot sun, wind, or rapid drying during the curing phase.
Most cement reach full strength potential after 28 days under suitable curing conditions.

Monitor dampness levels in the patch. Too little moisture prevents proper hydration while too much leads to a weak surface prone to cracking. Curing membranes can help retain moisture levels.

The repaired area can be put back into service once curing is complete. Cement crack repairs should perform well for many years with proper preparation and application.

Advantages of Cement Crack Repairs

Filling cracks and defects in concrete and masonry with cement mortar offers many benefits:

Long service life – Cement mortar provides a permanent structural repair that can last for decades.

Excellent bonding – Cement adheres tightly to cured concrete and masonry surfaces.
High strength – Properly cured cement mortar develops compressive strength comparable to surrounding materials.
Low shrinkage – Using appropriate mix design minimizes drying shrinkage.

Versatile – Cement mortar can patch holes, rebuilt joints, set anchors, and more.

Cement is also inexpensive and readily available. Installation does not require special skills beyond basic masonry or concrete work. Overall, cement offers a simple, cost-effective solution for crack repair in many common situations.

Potential Drawbacks of Cement Crack Repairs

Cement mortar does have some limitations as a patching material:

It is rigid when cured, lacking flexibility. Cracks may reappear if substrate movement continues.
Poor bonding can occur without proper surface preparation and application.
Cement has lower tensile strength than alternatives like epoxy.

Not suitable for dynamic or structural cracks subject to continuous movement.
May not perform well in moist environments or areas of freeze/thaw.

For best success, cement crack repairs should only be used where cracks are stable and are due to minor shrinkage, settlement, or stresses. Ongoing structural movement will likely cause patched cracks to reopen over time.

Alternatives to Cement Crack Repair

In some situations, cement mortar may not be the best choice for fixing cracks. Here are a few alternatives:

Epoxy injection – Penetrates into crack plane for structural repairs.
Polyurethane foams/sealants – Flexible fillers for shifting cracks.

Hydraulic cement – Fast-setting cement for water leakage.
Routing and sealing – Channel crack for flexible sealant.
Carbon fiber reinforcement – Externally bonded fabric strengthens cracks.

Professional guidance can help determine the most effective method. Factors like crack width, active movement, water exposure, and cost play into the repair selection.

Conclusion

Cement-based mortar provides an affordable, accessible solution for repairing inactive hairline cracks, small holes, eroded joints, and similar defects in concrete and masonry surfaces. With proper preparation and application, cement patching offers long-lasting repairs that restore structural integrity. It may not be suitable for all cracking situations, especially those involving ongoing movement or environmental exposure. Consider the specific conditions and demands before settling on cement as a crack repair method.