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Schematic of a supported slab on grade (C) Carson Dunlop Associates Concrete Slab Crack FAQs
Q&A on Concrete Slab Crack Diagnosis & Repair #5

Floor slab & tile crack diagnosis & repair questions & answers set 5.

This article series describes the types of cracks that occur in poured concrete slabs or floors and explains the risks associated with each, thus assisting in deciding what types of repair may be needed.

Page top sketch courtesy of Carson Dunlop Associates, a Toronto home inspection and education firm.

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FAQs on how to Diagnose & Fix Cracks in Concrete Floors

Shrinkage cracks in slab poured using Pene-Krete in South Texas hot weather (C) InspectApedia.com Dale HartThese questions & answers about the cause, diagnosis, cure or prevention of types of cracks in concrete slabs and floors were posted originally at CONCRETE SLAB CRACK EVALUATION - home - be sure to see that article.

Some of these Q&A were also posted first as comments on this page that you are viewing.

[Click to enlarge any image]

Photo: shrinkage cracks in a concrete slab in South Texas, poured / placed in July 2018.

On 2018-09-04 by (mod) - hairline cracks in concrete waterproofing coating

Larry: do some further investigating: are the cracks only in the waterproof coating?

Add an image so that we can take a look.

IF the cracks are just in the coating itself, which is most-likely if the cracks were not present in the wall before the coating was applied, then we're seeing a coating failure not a concrete structure failure.

While basement waterproofing coatings are appealing and inexpensive, if there is significant water entry that probably won't be enough.

See BASEMENT WATERPROOFING

On 2018-09-04 by Larry C

I just had my basement water proofed and now in 96 linear ft. of new concrete I have 22 hair line cracks should I be concerned

On 2017-09-20 by (mod) - crack evident in the travertine tile about mid residence that extends across the slab

Bill,

When I see cracks through ceramic tile atop a concrete floor AND when the crack is in a nearly perfectly-straight line mid-span, that is usually cracking occurring at a control joint in the original slab.

It's a bit late to do much now but if you have to pull the tile to repair the damage you'd cover the crack with a fabric and coating specifically designed to prevent small slab cracks or control joints from telegraphing up through the floor tile.

The best solution is prevention: we would have set a center tile grout line right over the control joint and we'd have grouted that line not with hard cementious grout but with a color-matched flexible sanded sealant that can accommodate a bit of thermal movement without cracking.

On 2017-09-20 by Bill

I live in Mountainous area of Las Vegas. Foundation poured approximately 11- years ago and is approximately 3600 square foot single level with slab on grade with supported on a shallow spread footing system bearing on the on-site soils that are described as silty sand and gravel, with bedrock located from 2 1/2 to 8 foot below grade.

The slab was poured with a fiberglass mesh as opposed to wire mesh.

No movement or cracks on interior or exterior walls;

However there is a crack evident in the travertine tile about mid residence that extends across the slab, starting at approximately 1/4 inch as measured in the exterior footing and extends across the slab to approximately a 1/16 inch crack as measured on the opposite side of the home.

There is no vertical displacement and the crack has not appeared to change in width over the period since home was built.

The grout line in this area of the tile is larger on the side of the home with the exterior foundation evealing a 1/4 inch crack and narrows into a small hairline crack as it progresses to the opposite side of the house.

The previous owner advised that this has been in this condition since early on, shortly after the home was built.

A couple of additional cosmetic hairline cracks represent in an area approximately 9-feet from this larger crack with no evidence of cracking on exterior foundation.

Seeking your thoughts on this foundation issue and what remediation would be suggested.

We would like to re-tile this area with comparable travertine tile to alleviate the cosmetic concerns, but am concerned that this may not be feasible with the condition of the foundation.

Would appreciate your thoughts and suggestions.

On 2017-08-02 by John

Early 2016 I bought a house that was supposedly built in 2012. After 3 months water came up through the floor.

This led me to the county building department to look at the paperwork. the inspection card has no signature on the foundation. Another leak appeared and i had to take the siding off to get to the leak.

What i found besides the frost zone fitting was installed wrong and would not drain after being turned off.

which is nothing compared to the framing issues I discovered. The siding is placed over the shear panel joint for joint,

There is no 2' overlap. I also discovered there is no fire blocking and the corners are single studs . Back to the concrete there are cold joints and voids and even holes big enough to see the plumbing that is not allowed to be in the slab according to the county codes and the blue prints call out no plumbing or other ducts etc in the slab.

The prints call out for mechanical vibration to consolidate the concrete. the building is only 20 x 24 and there are cold joints horizontally and vertically. The drywall is cracking everywhere and coming down from the ceiling. There is nothing that is up to code.

The county says they don't know how it passed. When I asked why the foundation was not signed off, they gave me some story about that has to do with raised foundations. This has become a nightmare. What I'm trying to find out is since the foundation is not signed off but a certificate of occupancy was issued.

Nothing else is up to code and the county says they don't know how it passed, the slab is cracking and shifting . Windows are getting hard to open. The slab has no integrity and it was actually done in 2008 not 2012 as advertised.

It was an owner / builder and the county points at him and he points at the county saying it passed. Any suggestions.

I feel the slab has to go and the rest of the building as well. It needs to be done right so I have the confidence in the structure and I could never sell it morally or ethically knowing all these problems exist. Thank You

On 2017-07-29 by Carlie

We are shopping for a new home. Today we saw a "dream" home. I almost couldn't believe we could ever have such a wonderful house! Gorgeous kitchen, office, 4 BDR on main floor plus upstairs BDR suite. WOW. The house was built in 2007.

It was a foreclosure and the inside has been completely repainted and carpeted.

The carpeting is a warning flag to me, as most homes I see have hardwood flooring or tile floors.

I was upstairs and noticed the floor sloped slightly from the exterior wall toward the stairs and attic entrance. We looked at the ceilings in the great room and there were parallel three dimensional lines. The lines aren't cracks, exactly, but appear as poor seams of drywall.

The screened porch had a crack from the exterior of the slab, under the screens, to the house, with one side of the crack about 1/8" below the opposite side of the crack. This house is a home I had only dreamed of, and it's affordable to us, but I told the realtor no, I see danger of cracked slab.

This is a once in a lifetime house for us, financially, and I'm haunted by the fear I was hyper vigilant over fears of foundation issues. (We can't have it inspected until we make an offer.) Does it sound like we were smart to walk away?

On 2017-05-03 by (mod) - Look closely at the crack for water stains

M

Look closely at the crack for water stains - signs that water has ever come up through the crack; if there are no signs of leakage, AND if you keep water away from the foundation by maintaining roof gutters and downspouts, you're probably ok.

Still if it were my house I'd seal the crack before proceeding. Water leaking up under a wood floor at some future date would destroy the mold and would perhaps create a mold problem.

On 2017-05-03 by Mlf

We just moved into our house and removed the carpet to put in Wood floors. When the carpet was removed a long crack was discovered that goes the width of the room.

Will this present problem if left as is or what should be done?

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