Concrete slab crack FAQs:

Questions & answers on diagnosing & repairing cracked, settling, spalling, heaving concrete roofs, floors, slabs.

This article series describes methods for repair of cracks that occur in poured concrete slabs or floors and explains the need for accurate crack cause diagnosis and impact on structure before repairs are attempted.

FAQS on Cracks in Concrete Roofs, Slabs & Floors

These questions and answers about fixing cracks in concrete slabs or floors were posted originally

at CONCRETE SLAB CRACK REPAIR - topic home - be sure to review the advice given there.

[Click to enlarge any image]

Our photo (left) shows sealant being applied to a sound but leaking concrete roof on a home in central Mexico.

On 2019-11-26 by (mod) - shrinkage cracks in concrete

That's a concrete shrinkage crack in your photo.

Shrinkage cracks occur at stress points in the slab or where there are variations in the slab thickness such as perhaps the path of the conduit.

These discontinuous, hairline cracks are not a structural concern in a floor slab.

On 2019-11-26 by Vampire

Hello everyone
I am seeing hairline cracks in bottom side of roof along electrical conduits in all my rooms and lobby area after 5years of construction of building.
Is it dangerous for structural safety?

On 2019-10-31 - by (mod) -

Kunai I'm unclear what we're looking at here - is this a concrete roof/ceiling? Or is it a foundation wall.

TO me this looks like a cold pour joint in a foundation wall that's leaking.

The "fix" depends on what part of the building we're seeing.

A leaky cold pour joint in a foundation wall is best sealed with a sealing mesh and coating on the foundation exterior; if this is really a roof, the roof covering such as a membrane will be the fix.

On 2019-10-31 by Kunal

My newly constructed slab has developed cracks in the ceiling side. when water is accumulated on the terrace, water drops drips.

Attached image. What is the reason? Still, plasterwork and waterproofing work is not done. Let me know how it can be fixed.

On 2019-05-24 - by (mod) -

Sounds as if the slab was poured on loose fill - could that be?

On 2019-05-24 by Nitin

When trying to repair inner slab, entire inner slab has fallen down
IMAGE LOST by older version of Clark Van Oyen’s Comments Box code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2018-08-15 - by (mod) -

Sorry I can't see nor know enough information to give a detailed reply, Tushar.

Basically find the point of water entry and seal or repair that from above.

On 2018-08-15 by Tushar Nag

Having crack beneath beam and water seepage what to do ?
IMAGE LOST by older version of Clark Van Oyen’s Comments Box code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2017-12-02 - by (mod) -

If there are no roof leaks i might try wire brushing off rust, coating with a binding agent, plastering over a layer of high Portland cement plaster

On 2017-12-02 by Samyak

Hi-

My home's roof contains reinforcement of iron rods with concrete but at the time of construction the clearance b/w reinforcement and below surface of roof was less than the diameter of rod so now after 15 yrs rods are coming out from the concrete.please suggest any repairment idea.

Question: hairline crack on concrete roof slab

(May 3, 2016) Mahta said:
Hair Crack on roof slab

(May 10, 2016) aditi said:
Sir, i have constructed my house roof one year back n in starting of rainy season i found cracks on my roof due to which there is leakage in rainy days. what is the cause n remedy for the cracks in my house roof.

Reply:

I can't diagnose nor suggest repair with just the information in your question.

Risks involved include at least these

1. Roof leaks
2. Frost damage
3. Structural damage

Start at SHRINKAGE CRACKS in SLABS

Aditi

You're asking a roof question on a concrete slab article. IF your roof is a flat concrete slab and is cracking, there are a variety of causes: sagging from improper construction or inadequate reinforcement would require structural repairs; cracks from concrete shrinkage can typically be patched and sealed.

If a concrete roof is leaking typical repair is to use a combination of synethtic fabric membrane and a concrete roof sealant mastic or paint.

Details are at FLAT ROOF LEAK REPAIR

Question: structural repair for sagging inadequately reinforced concrete roof

May 11, 2016) aditi said:
what kind of stuctural repairs can we have for cracks on roof if it is due to sagging or inadequate reinforcement.

Reply:

Aditi

Watch out you are describing what sounds like risk of structural collapse. A structural engineer is needed to make an on-site assessment and then describe what is a safe repair.

Typically we see emergency support provided from below (posts and beams below the roof).

A final repair could require either roof removal and then reconstruction or construction of a properly-reinforced concrete roof above or below the existing one.

Question: dips in newly poured slab

(May 28, 2016) Jesse Vasquez said:
I just had a concrete slab poured, 14 by 30, bromed! It looks like crap, how do I fix it ? There's dips n it's not good

Reply:

Jesse:

If you're not satisfied with the concrete work I hope you haven't paid the contractor.

What repair is needed depends on the nature of the problems. Brooming may be proper on some pours - such as a sidewalk, as an anti-slip measure - but would be an odd finish for a building interior floor.

Dips - depending on the amout of out of level a new cap slab could be needed, or simply a top coat with a concrete leveling compound.

Question: solution for crack on concrete roof when a beam is sagging

(Aug 17, 2016) shallu razdan said:
Sir plz provide any solution for crack on concrete roof which has occured since construction due to delection of beam support at that time

Reply:

Shally,

At FLAT ROOF LEAK REPAIR you'll find detailed procedures for successful sealing of leaks in a flat or low slope concrete roof, PROVIDED that structural repairs are not needed.

Watch out: A deflecting beam below a concrete roof needs evaluation by a civil or structural engineer. The risk is catastrophic structural collapse and injury or death to occupants.

First, you need an expert diagnosis of the crack that you described to answer at least these questions:

1. what caused the crack?

2. has that cause been reparied so that the cracking won't continue?

3. has the amount of movement caused other damage that needs repair?

4. How big is the existing crack? As that may affect the repair approach?

Once those questions are satisified, for hairline or small cracks, say up to a few mm in width, you might try any of the sealants described in the article above. On a roof surface I like to apply a synthetic fabric membrane over the crack area, sealing it to the roof surface, and then coating the membrane upper surface with a good quality roof sealant formulated for use on concrete. That membrane offers additional protection against re-opening of the repaired area and thus against leaks.

Question:

(Sept 4, 2016) Pranav said:

Sir, my house is constructed six years before , now these days of rainy season slap of the drawing room is breaking and large pieces of concrete (broken reinforcement started falling and portion where slab is bent and water leakage is there through crack.

It came to know now because there is POP in between. I have some photos of slab captured. Should i have to reconstruct slab or theirs any other way? How can diagnose broken rebars? Please give if theirs any solution.

Reply:

Watch out: you are describing crumbing, collapsing concrete roof construction. I cannot know and am not a concrete engineer, but from your description it sounds as if the concrete mix was improperly done, perhaps without enough concrete or reinforcement or both.

The risk is that someone could be killed by a falling roof. You need an onsite civil or structural engineer to assess the damage and then to help you decide what repairs are needed such as

- removal and reconstruction of the roof

- added reinforcement and support

- a new top layer of sealant or fabic + sealant

...

Continue reading at CONCRETE SLAB CRACK REPAIR - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• CONCRETE COLD POUR JOINTS
• CONCRETE SLAB CRACK EVALUATION
• CONCRETE SLAB CRACK REPAIR
• CONTROL JOINT CRACKS in CONCRETE
• CRACK REPAIR STANDARDS for FLOORS
• POLYURETHANE FOAM INJECTION CRACK REPAIRS
• SEAL CONCRETE CRACKS, HOW TO
• SHRINKAGE CRACK REPAIR
• SLAB CRACK REPAIR STANDARDS
• VERTICAL FOUNDATION MOVEMENT REPAIR
• FOUNDATION CRACK DICTIONARY since those pages also assist in distinguishing among types of cracking in concrete foundations (vertical supporting walls and footings

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CONCRETE SLAB CRACK REPAIR FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING STRUCTURES

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