If you want to know how to repair a concrete foundation that’s crumbling, you’re in the right place. Your foundation is a vital part of your home, and it needs to be constantly maintained and repaired when it’s damaged. This article explains why your concrete foundation is crumbling, how to repair a concrete foundation that’s crumbling, and how to prevent your concrete from crumbling in the future.

Why Is Your Concrete Foundation Crumbling?

If your concrete foundation is crumbling, it could be due to a process called scaling (or spalling). Often, scaling is when your concrete foundation is exposed to water that’s freezing and thawing, which causes it to crumble or chip. Scaling can also occur due to aging or if your foundation is frequently pressure washed or sandblasted.

Scaling may look like a simple cosmetic issue, but if it’s left untreated, it can turn into a structural issue over time.

Concrete foundation under construction

Freezing and Thawing

Concrete seems like a stable and permanent material, but it remains porous and will absorb water. When this water trapped inside the concrete freezes, it pushes the cement binder apart. This expansion, and the resulting contraction when the water melts again, causes crumbling. If you live in an area with winter temperatures low enough to freeze water, seal your concrete steps or walkway with a sealer once a year to keep water out.


Concrete requires an aggregate in the form of gravel. When the stone used for this gravel contains certain mineral deposits, these minerals leech out slowly and cause cracking and crumbling of the concrete. Pyrites are the main cause of this in residential concrete. Other minerals, including silica and mica, also cause deterioration when present in high amounts. Modern concrete testing standards prevent these problems in new concrete, but older concrete construction may be susceptible to this issue.

De-icing Salt

A frost-covered concrete driveway becomes slick and dangerous to walk on. Sprinkling a little rock salt may encourage melting and give you traction, but it will also damage the surface of the concrete. Rock salt, or sodium chloride, leads to pitting and crumbling of the surface of concrete due to a chemical reaction. Using alternative de-icing crystals like magnesium chloride or potassium chloride prevents this from happening.

Too Much Water

Concrete comes in a dry form, either as bags of cement or ready to mix with the gravel already added. It begins to set as soon as you mix in water because the cement reacts chemically to moisture. If you add too much moisture during the mixing phase, the chemical bonds that create a strong and durable concrete surface will be weaker says the Portland Cement Association. Use only as much water as the mix’s design indicates to prevent weak concrete that crumbles under pressure.

How To Repair A Concrete Foundation That’s Crumbling

Here’s how you can repair a concrete foundation that’s crumbling.

Preparing The Surface

  • The surface must be clean, sound, and free of frost. Remove all deteriorated concrete, dirt, oil, grease, and other bond-inhibiting materials from the area to be repaired.
  • Preparation work should be done by high-pressure water blast, scrabbling, or other appropriate mechanical means to obtain an exposed aggregate surface profile of ±1/16″ (1.6 mm) (CSP-5).
  • To ensure optimum repair results, the effectiveness of decontamination and preparation should be assessed by a pull-off test.
  • Saw cutting of edges is preferred and a dovetail is recommended.
  • Substrate should be Saturated Surface Dry (SSD) with clean water prior to application. No standing water should remain during application.
  • All the above recommendations must be followed.
  • The concrete must be frost-free before the application.
An industrial worker at a construction site installs a sealant for waterproofing cement. Worker puts liquid insulation on the floor. Workers applying the memory form of polymer waterproofing. Waterproofing concrete floor with mortar and brush.

PRIMING Reinforcing Steel

Steel reinforcement should be thoroughly prepared by mechanical cleaning to remove all traces of rust. Where corrosion has occurred due to the presence of chlorides, the steel should be high pressure washed with clean water after mechanical cleaning. For priming of reinforcing steel, use a proper material for the application.

Concrete Substrate – A scrub coat of appropriate material can be applied prior to the placement of the mortar. The repair mortar must be applied to the wet scrub coat before it dries.

Application Tips

  • The project-specific mixed materials must be worked well into the prepared substrate, filling all pores and voids.
  • Compact well. Force material against the edge of repair working towards the center. Thoroughly compact the mortar around exposed reinforcement.
  • After filling repair, consolidate, then screed. Finish with steel, magnesium, wood, plastic floats, or damp sponges, depending on the desired surface texture.
  • MULTIPLE LIFTS. Where multiple lifts are required, score the top surface on each lift to produce a roughened substrate for the next lift.
  • Allow preceding lift to harden and achieve the initial set before applying fresh material.
  • Saturated Surface Dry (SSD) previous lift by lightly misting with clean water. Remove all standing droplets.
  • Repeat the procedure until desired installation thickness is achieved. Finish the final lift of materials as described above.
  • If previous layers are over 6 hours old, mechanically prepare the substrate and dampen it.
  • CURING TREATMENT. As per ACI recommendations for Portland cement concrete, curing is required.
  • Moist cure with wet burlap and polyethylene, a fine mist of water.
  • Curing compounds adversely affect the adhesion of following lifts of mortar, leveling mortar or protective coatings.
  • Moist curing should commence immediately after finishing.
  • Protect freshly applied mortar from direct sunlight, wind, rain, and frost.
Process putty concrete wall with a metal spatula

Step-By-Step Process

  1. First, you’re going to want to remove any dust and loose concrete using a stiff scrub brush. You can also use a chisel, hammer, or a rotary hammer with a chisel tip to remove bigger crumbling pieces. (Save any larger chunks of concrete for later). Only remove concrete that is already cracked. You don’t want to chip away unaffected concrete. Then, use a garden hose and scrub brush to clean away dust and loose particles. Wait 24 hours for the concrete to completely dry before you move on to the next step.
  2. Now that you’ve waited 24 hours, you want to get the concrete slightly damp. You can use a sponge, brush, or spray bottle. Remember, you want the concrete damp, not soaking wet.
  3. You’re going to want to apply a cement paint or an adhesive primer before applying your patching material. This allows your patching material to bond to the old concrete. To make cement paint, mix Portland cement with clean cold water until it has the same consistency as latex paint. Apply the paint to the old concrete using a medium or large paintbrush.
  4. As soon as you’ve applied your cement paint to your concrete, you want to apply your patching material immediately. You’re patching material should be a ready-mixed concrete patching compound. You don’t want to fill in larger holes with only patching material. If you’re working in your basement, you shouldn’t have to worry about the sun, but if you’re working outside, try working in the shade or when the sun’s down.
  5. Apply a second coat of patching material after two hours. You want to make sure your walls are smooth and level. Finally, allow the patching material to cure in the open for 30 minutes.
  6. Lastly, cover the newly patched concrete with a plastic tarp, lightly spraying the area with water from a garden hose once a day for two days. Once the concrete has cured completely, remove the tarp, and congratulations, you’re all done!

Now, if your concrete is crumbling because of a structural issue and not a cosmetic issue, you will have to look into stronger solutions. Learn how to identify structural issues and the basics of basement wall repair.

How To Prevent Your Concrete Foundation From Crumbling

One reason your concrete foundation is crumbling is because it’s been exposed to water. Water can do all sorts of damage to concrete. One way to prevent your concrete foundation from crumbling is by installing a proper drainage system and directing acidic rainwater water away. Another way to prevent this is with the use of a penetrating concrete sealer. It is one of the most cost-effective ways to prevent crumbling and flaking. Penetrating sealer comes in many forms but most have several things in common. They don’t alter the appearance of the slab and they have a long effective life span.

Mini bulldozer with earth doing landscaping works level the ground
  • Clean your gutters – If your gutters become clogged, water can pour over the sides and drop right at the base of your foundation. Clean out all leaves, twigs, dirt, and anything else that could be clogging your gutters.
  • Extend your downspouts – If your gutter downspouts are pouring water too close to your foundation, your concrete can crumble. If your property is very flat, we recommend having them drop water at least 10 feet away from your home.
  • Add an interior or exterior drain tile system – A drain tile system is made of a perforated (pierced with small holes) pipe and a bed of washed stone. For an interior drain tile, the pipe is laid underneath your slab floor. For an exterior drain tile, the pipe is placed outside your foundation walls. Both drain tile systems connect to a sump pit, where a sump pump ejects any collected water outside of your home.
  • Add a French drain – French drains work similar to a drain tile system, except instead of being placed around your foundation perimeter, they’re placed in your yard at ground level. French drains are used to prevent water from pooling in flat areas of your property. French drains carry any collected water to the lowest part of your yard, a drainage ditch, street gutters, or a dry well (an underground structure that disposes of unwanted water).
  • Improve your grading – The soil around your house should slope at least 6 inches within 10 feet away from your foundation. This sort of project requires a lot of dirt and physical labor. You better leave this to the professionals.

Read more about how to drain water away from your foundation.

Who Do You Call For Professional Solutions

If you need professional help, call Foundation Professionals of Florida, an award-winning and top-performing company. Call us, and we can find out why your concrete foundation is crumbling, repair the damage, and prevent your concrete foundation from crumbling in the future. We also specialize in foundation waterproofing, crawl space repair, crawl space waterproofing, concrete lifting, and more.