Questions & answers about concrete slab crack control joints and cracks at control joints.

This article series describes the causes, evaluation, and repair of cracks at control joints in poured concrete slabs or floors.

How to Use & Inspect Control Joints in Poured Concrete Slabs

These questions and answers about control joints to prevent or repair cracks in concrete slabs were posted originally at CONTROL JOINT CRACKS in CONCRETE - be sure to review that article.

Separately at CONCRETE SLAB CRACK EVALUATION we catalog the different types of cracks that show up in poured concrete.

2018/11/09 (mod) said: - what is the proper delay before cutting control joints in a new concrete slab?

Karen

As long as the control joints are properly cut after the slab is poured, I would be stunned to hear of a report anywhere claiming that the 9 day delay in creating those control joints created itself any problem in the slab.

The concrete has only barely begun to cure in the first nine days of its life and the stress is continue to develop over a much longer period. Even if there were already stressors in the slab they're relieved by the control joint.

I did some research to see if I could find any expert expressing a different View.

Interestingly in some situations, a seven delay between placement of a new concrete slab and cutting-in of control joints is actually necessary in some cases to permit proper cuts without damaging the slab.

Research Citations on delay in cutting control joints in concrete

• Armaghani, Jamshid, and Diep Tu. "Rehabilitation of ellaville weigh station with ultrathin whitetopping." Transportation Research Record: Journal of the Transportation Research Board 1654 (1999): 3-11.
• Chiuminatta, Edward, and Alan R. Chiuminatta. "Apparatus and method for cutting unhardened concrete." U.S. Patent 5,184,597, issued February 9, 1993.
  
  Excerpt:
  |
  Conventional practice has been to cut crack control grooves in the concrete as soon as possible, and about 7 days later, to use diamond abrasive water saws to cut over the crack control grooves and form a wider, shallower well into which the sealant is placed.
  
  Since the sealant well is so much wider than the crack control grooves, the concrete must be allowed to become very hard to avoid cracking, chipping, and spalling of the concrete when the 0.25 or 0.375 inch wide groove is cut to form the well for the sealant.
  
  Thus, the seven day delay is often required to insure the concrete is sufficiently hard and will not crack, chip, or spall when the wide groove for the sealant well is cut in the surface of the concrete.
• Chiuminatta, Edward, and Alan R. Chiuminatta. "Apparatus and method for cutting unhardened concrete." U.S. Patent 5,507,273, issued April 16, 1996.
• Gerald F. Voigt, P.E., Specification Synthesis and Recommendations for Repairing Uncontrolled Cracks that Occur During Concrete Pavement Construction, [PDF] ACPI, Gerald F. Voigt, P.E., Vice President - Technical Operations, American Concrete Pavement Association, 5420 Old Orchard Road, Suite A100, Skokie, IL 60077-1059 USA, Tel: 847-966-2272; Email: gvoigt@pavement.com, retrieved 2018/11/09, original source: 1204075.sites.myregisteredsite.com/Downloads/Cracking.pdf
  
  Excerpt:
  
  Mixtures containing certain fly ashes or lower quantities of portland cement can delay early age strength development in cooler weather.
  
  Depending on the air and concrete temperature, this could delay concrete setting and the ability to saw without excessive raveling.
  
  After setting, the time available for sawing before the onset of cracking may be much shorter than normal.
• Hanson, Raymond A. "Joint forming apparatus for concrete surfaces." U.S. Patent 3,381,595, issued May 7, 1968.

2018/11/08 KarenKenny said:

We are in the process of having a home built. The 2100 square foot basement and 1200 square foot garage were poured cut the supervisor forgot to have contraction joints cut until 9 days after the pour.

I know the concrete will crack, all concrete does with or without cuts. My questions are 1) what is your best guess of what the effects will be...how bad? 2) is there anything we can do to reduce the impending damage?

(Aug 21, 2018) (mod) said -

Probably yes but it would be better to use a flexible sealant normally used for control joints in concrete

(Aug 21, 2018) Robert Berryman said:

Crack in walkway about 5 foot across can I cut a straight line and insert a board
How do I seal it

(May 22, 2018) (mod) said -

Sorry but I don't understand the question.

Concrete shrinks as it cures, the rate and cure time depending on mix and site conditions but generally most curing is in days, final curing months. But it also responds to changes in temperature and moisture so I would not claim that after a certain point concrete around an expansion joint never moves again.

(May 22, 2018) Danny said:

How long will an expansion joint take before it will not move on a poured slab?

(Dec 27, 2017) (mod) said -

The width of the expansion joint you cite might be necessary depending on the flooring materials, thickness, dimensions, and climate. Or you could cut several spaced-out expansion joints through the slab onto which the tile is set, placing the cuts exactly at tile grout joints.

Then as you tile along the joint, use a matching flexible sealant rather than grout in those joints.

(Dec 27, 2017) Anonymous said:

We have an old German home with an obvious expansion joint cut right in the middle of the old tile and we want to retile the floor. Do we need to keep the large 1/2 inch gap when we retile?

(Sept 20, 2017) Leo said:

My contractor pour me a 20'x40' concrete slab for my RV pole barn. It's been nearly 3 weeks and I just realize that no cuts were made on the slab. Should I have him donut now or is it too late

(Sept 6, 2017) (mod) said -

Sorry Free,

To protect reader confidence we do not offer any for-sale product nor service.

I can offer suggestions, look at photos, refer you to technical articles that give greater depth or how-to advice for diagnosing and fixing problems such as the driveway cracking you are understandably finding aggravating.

Use the page bottom or top CONTACT link to send me some photos and I can comment further.

The problem could be a bad mix, bad pour, bad site preparation (pouring over soft fill), or something else. 21 cracks sounds like more than a control joint omission problem.

Editor (DF)

(Sept 6, 2017) Freedom Ostergaard said:

We are having terrible cracking with our newly poured driveway. At last count 21 cracks all which are from joints not being placed correctly. Do you offer consulation? I would love to send pictures and get your take! My email ostyfam@charter.net

(Sept 23, 2016) (mod) said:

The "worst thing" that could happen is perhaps something beyond what I can guess from a one-line e-text: something that an expert, on-site, may be able to determine.

The more likely "thing" that you could see that would also be a problem would be a cold pour joint that could be a roof leak requiring patching or sealing.

Whether or not a cold pour joint in a concrete roof is also a roof leak depends on both the specific joint - including luck - properties, and more on what sort of roof covering or coating will be applied to the completed structure. If the roof is to be covered with a membrane or sealant or other layer, the joint could be unimportant.

(Sept 23, 2016) Shyama said:

When we were doing our roof TOP concrete (6 inches thick) ,due to delay in arrival of concrete trucks ,there was a 5hour delay between two successive concretes.What is the worst thing that can happen and how can it repair

(Mar 21, 2016) (mod) said -

Not necessarily; you want to understand the cause of the cracks so as to know what to expect. Look into concrete slab patching fabrics and adhesives intended to be used under tiling jobs.

(Mar 21, 2016) James said:

I am tiling over an old, cracked slab at approximately 2000 square feet. Do you recommend cutting "relief" joints in the existing floor and what about the tile itself.?

(Nov 9, 2015) Richard Woyce said:

Thank you very much for the quick reply. I just north of Atlanta so there is a chance of freezing and good guess it is built on top of a lot of good Georgia clay.

Thanks again - Rich

(Nov 9, 2015) (mod) said -

Richard

Thanks - that's an interesting question. You don't say where you live. If we send water below a floor slab in an un-heated space in a freezing climate we indeed might get frost heave and crack damage - that may occur also over expansive clay soils.

So I think it'd be clever to use a flexible sealant in the crack: that won't interfere with the control joint's ability to do its job and it'll keep water from entering the floor and maybe pests from visiting from below. I like polyurethane sealants such as those used in radon mitigation. Vacuum out the crack of loose dirt and debris, be sure it's dry, and caulk to a concave surface below the actual floor surface.

(Nov 9, 2015) Richard Woyce said:

My house was built in 1989 and the expansion / control joint in the garage slab has a crack running pretty much its entire length. I know that is a "good" thing as it cracked in the control joint but should I go back now and fill the crack with a flexible sealer to prevent water and other debris from getting below the concrete in the garage floor. I do wash it out from time to time with a hose.

(Aug 2, 2015) (mod) said -

Ann

Find our email at the page bottom CONTACT link to send me some photos for comment - I'd like to see the details.

What are the dates involved: dates of construction, floor installation, first observation of a problem.

How is the hardwood floor installed? Nailed to sleepers, glued, floating with clipped connections, what?

What underlayment was placed under the flooring and over the slab?

What direction does the flooring run with respect to the control joints that you suspect?

What is meant by "backsies" ?

I'd hold off on any costly steps before we are quite confident about the cause and thus the remedy.

(Aug 2, 2015) Ann Campbell said:

He put it in the report. No backsies!

(July 31, 2015) ancb12 said:

Shortly after purchasing our new construction home we noticed that our hardwood floors on our monolithic slab we separating. After walking the exterior of the home we discovered that along the same lines/areas that the hardwood flooring is separating there are cracks visible on the exterior of the foundation.

We have only been able to investigate under the carpeted areas in our home as majority is hardwoods and have located the cause of the hardwood flooring separating, control joints. We believe the 4 control joints (2 north to south and 2 east to west) are much to wide and deep (we have pictures during construction that show their placement).

They are approx 1/2” wide and have large cracks in them that appear to have cracked all the way down to the vapor barrier (I'm also concerned about moisture as the hardwood flooring is splintering and separating underneath the top). This is a huge concern for us as almost every room on our lower level has a joint running through it.

The builder sent his engineer to look at the areas under the carpet (since the rest is under the hardwoods) and the engineer stated the joints should be 1/8” not 1/2” wide. He said that all the areas under the hardwoods would need to be stitched in addition some type of underlayment over the joints before reinstalling the hardwoods and the areas under the carpet would just need pressure epoxy and that we will continue to have problems unless it is addressed.

He put this all in a report as well. The builder agreed to fix the issues. A few weeks later the builder and the engineer showed back up and the engineer stated he was mistaken and to disregard his state sealed report that the joints are not too large. Now the builder will not fix the control joints in the slab.

We are concerned as this seems like it would be very costly to fix in addition the 2000 square feet of hardwood flooring will have to be removed and replaced. We feel potentially the value has/will decreased as we would need to disclose this when we sell our home. This isn't a job we can afford to fix ourselves. Any other opinions if indeed the joints are too large and if the engineer's initial remedy is correct?

Reader Comment: weather conditions impacted concrete slab cracking

(Oct 2, 2014) scott At- ranchodlux@yahoo.com said:

I have a slab floor in my basement its 26'x 44'and it has control joints in it 1 down the center length wise and 2 across (they cut the slab in to 6 pcs) and I have shrinkage 8 yrs later each joint is different ranging from 1/4" to 3/4" separation

This slab was poured on a sunny hot windy day couldn't have had a worse day for a pour LOL Why 8 yrs later ? oh and the slab was poured before the house was built and it is a walk out basement.

Reply:

It's not surprising that concrete shrinkage might show up as varying widths between multiple control joints in a poured concrete floor as there are additional variables both among individual pours such as differences in soil compaction, water content of soil and concrete, even pour conditions.

But if you are seeing new settlement or movement I'd look for a problem with expansive clay soils (we don't know where you are located) and/or control of surface or roof water runoff that might impact the foundation and floor slab.

...

Continue reading at FREEZING & WATER DAMAGED SLABS 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 FOUNDATION, WALL, SLAB DEFECTS
• CONCRETE REINFORCEMENT, FIBER
• CONCRETE SHRINKAGE CRACKS
• CONCRETE SLAB CRACK EVALUATION
  • CONTROL JOINT CRACKS in CONCRETE
  • FREEZING & WATER DAMAGED SLABS
  • FROST HEAVE / EXPANSIVE SOIL CRACKS in SLABS
  • SETTLEMENT CRACKS in SLABS
  • SETTLEMENT vs. FROST HEAVE CRACKS
  • SETTLEMENT vs. SHRINKAGE CRACKS
  • SHRINKAGE CRACKS in SLABS
  • SHRINKAGE CRACKS at FOUNDATION WALLS
  • TEMPERATURE EFFECT on CONCRETE POUR
• CONCRETE SLAB CRACK REPAIR

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CONTROL JOINT CRACKS in CONCRETE FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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