Concrete slab cracks heaves form trip hazards (C) Daniel Friedman Concrete Roof or Floor Crack Repair FAQs

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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.

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Cracks in Concrete Roofs, Slabs & Floor Questions & Answers

Flat roof leak diagnosis & repair (C) Daniel Friedman[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.

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.


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



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.


Question: structural repair for sagging inadequately reinforced concrete roof

Cracks in a concrete slab in an Alaska home over thawing permafrost (C) D FriedmanMay 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.



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



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



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.


(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.


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 or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Or see FOUNDATION REPAIR METHODS and see SINKING BUILDINGS where we include case histories of both building settlement and slab cracking, heaving, settling: diagnosis and repair.

Or see FOUNDATION CRACK DICTIONARY since those pages also assist in distinguishing among types of cracking in concrete foundations (vertical supporting walls and footings).

Or see these

Concrete Crack Diagnosis & Repair Articles

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