The Causes of Basement Floor Cracks and the Cost to Repair

In this Home Flooring Pros How-To post we examine hairline cracks, spalling, foundation wall cracks, cracks caused by settling and cracks cause by sinking slabs. In each instance we show you what can be done about fixing them (if indeed they need fixing) and how much each crack repair will cost, both DIY and professional contractor. Filling and repairing basement floor cracks is an important step in basement floor waterproofing.

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TYPES OF BASEMENT CRACKS – CAUSE AND CURES

Basement floor cracks are inevitable. But don’t let that startle you. Most cracks in basement floor are not a cause for concern.

Here are common types of basement floor cracks, what causes them and what you should do to repair them – if they need repair at all.

HAIRLINE CRACKS – OR THOSE A LITTLE BIGGER

Small surface cracks, aka hairline cracks, are common and nothing to worry about. They are the first to show up – often within a year of when the concrete floor was poured. As the concrete fully cures over months, minor shrinkage causes the surface to crack.

Identifying Hairline Cracks: These cracks are shallow, maybe 1/32 of an inch. No water oozes from them. Hairline cracks are jagged, straight or a bit of a jumble. The concrete remains level – no sinking or rising of the slab in the vicinity of the cracks.

Fixing Hairline Concrete Cracks: Structurally, hairline cracks are not a threat to your basement floor.

However, if you don’t like the looks of them, you have two options:

Cover the basement floor in flooring designed for below-grade installation. Be sure to purchase quality waterproof basement flooring, so normal basement humidity won’t cause mold and musty smells.

Cover cracks with a concrete resurfacer like those from Quikrete and NewCrete. The Quikrete product label says it is, “a special blend of Portland cement, sand, polymer modifiers…designed to provide a shrinkage-compensated repair material for making thin repairs to sound concrete which is in need of surface renewal.”

Shop Concrete Resurfacer from The Home Depot

Does that sound like the right cure for your basement floor cracks? It will fill and seal the cracks, but the treated area will have a different color and look unless you do the entire floor, and either way you might not like the visual. If you don’t, revert back to the discussion of basement floor covering options.

Slightly larger cracks: Once cracks in basement floor surfaces worsen to about 1/8” wide and/or deep, consider filling the crack with a caulk designed for concrete.

Most are elastomeric, meaning they do a good job sealing the crack and have enough elasticity to flex a bit as the crack expands or shrinks with normal movement in concrete.

For example, Dap makes one called Extreme Stretch Premium Crackproof Elastomeric Sealant for about $7 per 10-ounce tube. Dap claims it is, “Formulated to stretch over 600% without losing adhesion.” That means it should stick to the sides of the crack and stay in place even with additional worsening of the crack.

Shop Dap and Other Concrete Caulk from The Home Depot

Definitely fill deep cracks. Deep but narrow cracks aren’t cause for major worry, but if they go all the way through the slab to the soil below, they might allow dirt smells and, worse yet, gases like radon to seep up into the basement. Elastomeric caulk should do the job – and if you’re concerned about the situation, call a concrete contractor for guidance and professional remedy of the crack or cracks. A basement radon test is never a bad idea.

SPALLING

Spalling is the general deterioration of the surface of the concrete. It is usually widespread, often showing up first in high traffic areas.

This problem won’t affect the structure of the floor, but it does indicate the concrete had too much water in it when poured. Water rises in the mix and weakens the surface, so it crumbles under weight. If spalling occurs in a floor you paid to have installed, call the contractor and expect them to provide the remedy at their cost – usually a resurfacing of the floor.

Repairing Spalling

There is no perfect fix for spalling short of tearing out the slab and starting over. Since that’s not gonna happen – and there is no need for it – you’ve got the same choices as those for dealing with minor cracks which is to say resurface your concrete or install a floor covering using, typically, a basement floating floor system.

Interested in Installing a Basement Floor? Check Out These Two Popular Options:

• Best Laminate Flooring for Basements
• Best Cork Flooring for Basements

CRACKS AT THE BASE OF FOUNDATION WALLS

Concrete can shrink a little as it cures, especially if steel reinforcement rods, or re-rod, isn’t used to fix the slab to the wall, Since that is rarely done, a common result is that the slab pulls away from the foundation wall, leaving a gap that is usually as deep as the slab.

This means odors, gas and moisture can rise through the gap from the soil below.

Fill these gaps! Elastomeric caulk, mentioned above, is the material of choice. And DIY is fine – but you’ll need a lot of caulk.

You might find that hiring a contractor is a cost-effective option – certainly one that will save you a lot of time. If water is coming up through the gap, then we definitely recommend having a pro assess the issue and recommend the best solution.

Pro Tip: Don’t use a basement floor sealer as a waterproofing solution on floor joints.

BASEMENT FLOOR CRACKS CAUSED BY SETTLING

Because concrete is so heavy, it will crack and settle if given the chance. Failure to use a deep layer of compacted sand as the foundation for the slab, or the sand being washed out by water flowing beneath the slab, give the slab the chance it needs. The poorly supported section will sink, cracking at the stress point.

No water – When the crack remains dry, the issue isn’t serious. The recommended repair is to:

• Seal the crack with elastomeric caulk.
• Use self-leveling concrete on the sunken area to make it level with the surrounding concrete.

Now you’re going to have two different surfaces – the original and the self-leveling concrete. If appearances matter, you’ll definitely want to consider flooring which can be as simple and affordable as basement gym flooring.

Note on new concrete slabs: If the slab is less than 2 years old, it might continue to settle. Can you “live with” the crack a little longer? You might want to wait until the concrete is 2-3 years old before making the repair, hopefully once and for all.

Water – When the crack caused by settling oozes water or odors, there is greater cause for concern. The no-water approach above might work, but it won’t hurt to get a free estimate from a concrete contractor.

Pro repair would likely involve injecting polyurethane into the crack(s) to form a permanent waterproof seal before using self-leveling concrete on the sunken portion.

CRACKS WITH SINKING OR HEAVING SLABS

OK, now we’re talking about cracks in the basement floor that do affect its structural integrity.

Is a section sunken by more than one inch? Is a section raised (heaved) at the crack? Are odors and moisture present?

Major cracks in basement floor sections should be addressed. For serious damage, the sunken section should be raised, often called slab-jacking or mudjacking. Or it should be broken up, removed and replaced.

Slab-jacking – Material, often polyurethane foam, is injected through holes drilled into the slab. The material is under enough pressure to raise the concrete slab back into place.

Section replacement – If there is concern that the underlying soils will continue to cause sinking, it might be better to remove the sunk portion. Then, the unacceptable soils – often clay which absorbs water and causes heaving – can be removed and replaced with sand. Compacted sand can then be safely covered with a new section of concrete slab.

COST TO FIX CRACKS IN BASEMENT FLOOR

Here is the basement floor crack repair cost for each of the repairs discussed.

Crack and gap filling – Tubes of elastomeric caulk cost about $7-$10 per tube. A 10-ounce tube will fill 50 feet of shallow cracks. It might take one tube per linear foot of gaps at the foundation wall. A decent caulk gun runs $12-$25.

Concrete resurfacing – Resurfacing mix runs about $30 for a 40-pound bag. You’ll get 40-50 square feet of coverage per bag when mixed.

Self-leveling concrete – A 50-pound bag runs about $35-$40. Rapid Set says its product covers 12 square feet to 1/2” thick – twice that for 1/4″ and half that for 1” thick.

Slab-jacking/Raising sunken concrete sections – Expect pro estimates in the range of $10-$15 per square foot. Factors include the size of the area (cost per square foot goes down a little as size increases) and how much the slab needs to be raised.

Concrete removal and replacement – Removing the damaged chunk of slab costs an average of $10 per square foot. Improving the material beneath the slab and pouring new concrete costs about $6 per square foot. Total cost average is $14 to $18 per square foot.

DIY REPAIR OF BASEMENT FLOOR CRACKS – YES OR NO?

You can certainly tackle the repair of surface/hairline cracks, spalling and gaps at the edges of the slab when no water is present.

Using self-leveling compound on sunken sections, again when water isn’t an issue, is within the skill set for handy homeowners.

When water issues need to be addressed, we recommend at least consulting concrete contractors about your options and costs.

If slab-jacking is needed or a section of slab has to be removed/replaced, then hiring a licensed and insured contractor is your best option for a long-term, effective repair.

About the Author:

Rob Parsell

Rob joined the Home Flooring Pros team in 2014 and is a freelance writer, specializing in flooring, remodeling and HVAC systems (read more).

“I’m the son of an interior designer and picked up an eye for design as a result. I started hanging wallpaper and painting at 14 and learned enough on the job to be the general contractor on two homes we built for our family and did much of the finish plumbing, electrical, painting, and trim work myself.”