Thread: Cracks on basement floor

Hi All, Hope someone can help me with this. 2003 Home 3850sq. Found these cracks in 3 places in the basement floor. They are 1.1/2 deep and 1/4 wide with some type of white material between the crack. They run the length of the floor. The seller who is also a builder claims they are control joints. I've never seen control joints likes this, especially that deep. Any help Id in this will be helpful before I write up the report.

THANKS ALL IN ADVANCE100_3583.JPG100_3597.JPG100_3598.JPG

They are control joints made out of plastic. They are placed before the concrete is poured and extend most of the thickness of the slab.

Mark thank you so much. Big help and learning experience for. Have a great weekend

- - - Updated - - -

Mark thank you so much. Big help and learning experience for. Have a great weekend

Originally Posted by Mark Reinmiller

They are control joints made out of plastic. They are placed before the concrete is poured and extend most of the thickness of the slab.

Mark, I forget to ask, if you know when they started using that technic for control joint

Originally Posted by fidel gonzales

Mark, I forget to ask, if you know when they started using that technic for control joint

I really don't know. I guess I have seen them used occasionally for at least 10-15 years.

The surface of the concrete was floated with a helicopter, a gas powered surface finishing tool.
I do not believe that is a control joint.
The grove would be 3/8" in depth from the surface down and every 8 feet.
The top would be straight with the concrete slightly jagged to the bottom when the control joint moves.

The slab crack runs straight but the surface face is not straight.
That appears to be caused from thermal expansion or movement. My opinion, thermal expansion from a mechanical system or utility pipe.
control joint in concrete..JPG
I have control joints in my basement garage that are doing there job.

I suspect there is something under the surface.
Maybe mechanical or a utility pipe as expressed above...

Next time you see that type of fracture in concrete, tap the surface with the back of a substantial plastic screw driver handle or small mallet if you carry one, and continue tapping away from the crack. If the sound changes it may mean a duct is under the floor. The thicker the concrete the higher the pitch or the tighter the vibration waves and it returns quickly . A high (tap - tap - tap) A hollow or void under the concrete would be lower pitched sound (thud - thud - thud)
Like a drum set. Tom tom's are low in sound where as the snare drum is (rat a tat tat)
I have read were in some homes in the US they installed furnace of HVAC chase work in slabs.

Its nice and straight thought.

Hypothesize!
Was there a load beam above in the ceiling running parallel? That would leave 2 footings to ether side, correct?
A working hypothesis would have me following and referencing that line around the perimeter of the home.
I would think of that line while inspecting the interior and exterior materials and components.

All the best.

Originally Posted by ROBERT YOUNG

The surface of the concrete was floated with a helicopter, a gas powered surface finishing tool.
I do not believe that is a control joint.
The grove would be 3/8" in depth from the surface down and every 8 feet.
The top would be straight with the concrete slightly jagged to the bottom when the control joint moves.

The slab crack runs straight but the surface face is not straight.
That appears to be caused from thermal expansion or movement. My opinion, thermal expansion from a mechanical system or utility pipe.
control joint in concrete..JPG
I have control joints in my basement garage that are doing there job.

I suspect there is something under the surface.
Maybe mechanical or a utility pipe as expressed above...

Next time you see that type of fracture in concrete, tap the surface with the back of a substantial plastic screw driver handle or small mallet if you carry one, and continue tapping away from the crack. If the sound changes it may mean a duct is under the floor. The thicker the concrete the higher the pitch or the tighter the vibration waves and it returns quickly . A high (tap - tap - tap) A hollow or void under the concrete would be lower pitched sound (thud - thud - thud)
Like a drum set. Tom tom's are low in sound where as the snare drum is (rat a tat tat)
I have read were in some homes in the US they installed furnace of HVAC chase work in slabs.

Its nice and straight thought.

Hypothesize!
Was there a load beam above in the ceiling running parallel? That would leave 2 footings to ether side, correct?
A working hypothesis would have me following and referencing that line around the perimeter of the home.
I would think of that line while inspecting the interior and exterior materials and components.

All the best.

Robert, thank you for taking time to respond. Very helpful information for the next time I ran into this. In your opinion do you think my client has anything to worry about with the cracks ?

Looks like a control joint to me too. Unless I'm looking at something else it looks like you can see the plastic from the Zipstrip (or similar) in the crack, the white material you mention.

In basement and garage floors around here contractors like to use Zipstrips instead of a saw cut, or grooved joint. This way, the floor looks good at the time of sale, and the builder gets to explain later on that all concrete cracks when the homeowner calls about the floors cracking after they move in. The Zipstrip joint is covered when they finish the floor, and when the concrete cracks it will have a rough edge.

A control joint is used to create a weak point in the floor, so when the concrete cracks, it cracks at the control joint in a nice straight line, in theory. I see concrete cracks at the control joints all the time around here in floors.

If the floor is even on both sides of the crack and the crack is straight, I would not lose sleep over it.

Originally Posted by fidel gonzales

Robert, thank you for taking time to respond. Very helpful information for the next time I ran into this. In your opinion do you think my client has anything to worry about with the cracks ?

Not being able to be there and run my routine, which has limitations, I can only make an opinion on what you have exampled in your narrative and images.

Personally, if that was the only defect in the slab, or lets say a deficiency in the assembly, then I would note it softly in the report and the narration, post inspection review for the client.
If I observed a chase,vent or other pathway for the HVAC, or a pipe, I would recommend "further review by a trade or technician."

Let me go one step further in creating "my working hypothesis' on a situation like this.
A long metal or/and non conductive but thin & flexible probe, IE a electrician's fish, can follow pathways. Again using your senses, sight, feel, hearing, to analyse if there is a structure or system component in non visual cavities.
I have 2 borescopes. One for sale. Never used
Lets remember, the residence is a assembly of components. What lay under or in-between the assembly must be extracted through non destructive - non invasive means to be compliant with my SOP.
No joke, we are not Mike Holmes inspectors. Non destructive - non invasive.
This man single handedly duped the government's into believing his version of what he did not and still does not understand, SOP, yet built a franchise off the backs of the government and educators, Sault Collage if I am not mistaken.
Now we homies in Canada are feeling the capitalist effect of one major insurance player capitalizing on the "save me from my competitor" with rising E&O fees as they maneuver to control E&O in Canada with Mike the mouth Holmes at the table in Ontario as all provinces and the federal government await this 3 year study.
Jesus mate!
Sorry for going off post.

Observation: Uniform Concrete Slab crack in the basement flooring.
Recommend: Yearly observation.
Condition: Straight 1/2" inch, uniform.

All the best.

They have been around for at least 20 years, my house built in 1994 has them.

All those pieces in the slab do is create a cracked control joint which is not as wide as a tooled cracked control line, but which is deep enough to actually better control where the concrete cracks [concrete does two things:1) gets hard 2) cracks].

The concern, is not what is in the cracks but why the cracks is that wide when the cracks control insert is so thin. Typically, cracking concrete create a cracked ... but no separation.

CONCRETE SLAB KEY-JOINT FORMING MEMBER

1969
Possibility of what may have been used, whether steel or plastic.

It is possible that the excessive water/cement ratio might have caused the excessive shrinkage in the slab.
There does not appear to have a differential movement between the two.
Whatever screed key was used, it should have been closer to the top surface creating a straighter break, but that is just asthetics at this point.
I do not see any problem with those pictures.

Originally Posted by Jerry Peck

All those pieces in the slab do is create a cracked control joint which is not as wide as a tooled cracked control line, but which is deep enough to actually better control where the concrete cracks [concrete does two things:1) gets hard 2) cracks].

The concern, is not what is in the cracks but "why the cracks is that wide" when the cracks control insert is so thin. Typically, cracking concrete create a cracked ... but no separation.

It is not what is in the cracks.
Not necessarily.

Shrinkage will cause slight separation from surround components and materials. concrete shrinks.
A bad batch shrinks more.

Jerry, not to take anything away from your post but what goes into concrete may be the deficiency.
What is in concrete as a whole is beneficial.
1: Reinforcement bar of lath are beneficial.
2: The proper consistency of the mix is another.
3: The proper cure time. Temperature and humidity are all relative to strength.

Metal HVAC vents and metal piping or utility conduit have been banned from floor slabs for some time I believe. I have seen more that one image from a homie on a message board with a HVAC vent being the culprit to a crack like that.
NOTE: I am not saying that this is the case here though.
I am trying to be subjective and allow the homies to ask questions and then verify the answers if permitted.
That's what is important in my opinion.


The width in separation should be what is calculated. Even if it is a shallow slab.

Regards. I was thinking the same thing after I sent the post.

Originally Posted by Marcel Cyr

CONCRETE SLAB KEY-JOINT FORMING MEMBER

1969
Possibility of what may have been used, whether steel or plastic.

It is possible that the excessive water/cement ratio might have caused the excessive shrinkage in the slab.
There does not appear to have a differential movement between the two.
Whatever screed key was used, it should have been closer to the top surface creating a straighter break, but that is just asthetics at this point.
I do not see any problem with those pictures.

I see those in large commercial and highrise slabs, not in residential slabs.

Not saying that they should not be used in residential or that they are not used in residential, only that I have not seen them used in residential - not even in the 25,000+ sq ft houses I inspected.

I was wondering if the slab was poured over a heel to the footing.

Originally Posted by ROBERT YOUNG

The surface of the concrete was floated with a helicopter, a gas powered surface finishing tool.
I do not believe that is a control joint.
The grove would be 3/8" in depth from the surface down and every 8 feet.
The top would be straight with the concrete slightly jagged to the bottom when the control joint moves.

The slab crack runs straight but the surface face is not straight.
That appears to be caused from thermal expansion or movement. My opinion, thermal expansion from a mechanical system or utility pipe.
control joint in concrete..JPG
I have control joints in my basement garage that are doing there job.

I suspect there is something under the surface.
Maybe mechanical or a utility pipe as expressed above...

Next time you see that type of fracture in concrete, tap the surface with the back of a substantial plastic screw driver handle or small mallet if you carry one, and continue tapping away from the crack. If the sound changes it may mean a duct is under the floor. The thicker the concrete the higher the pitch or the tighter the vibration waves and it returns quickly . A high (tap - tap - tap) A hollow or void under the concrete would be lower pitched sound (thud - thud - thud)
Like a drum set. Tom tom's are low in sound where as the snare drum is (rat a tat tat)
I have read were in some homes in the US they installed furnace of HVAC chase work in slabs.

Its nice and straight thought.

Hypothesize!
Was there a load beam above in the ceiling running parallel? That would leave 2 footings to ether side, correct?
A working hypothesis would have me following and referencing that line around the perimeter of the home.
I would think of that line while inspecting the interior and exterior materials and components.

All the best.

Robert, you are entitled to your opinion, but it is a control joint formed with a plastic strip (as someone noted, Zipstrip is one brand). This strip has a top piece that is pulled off after the concrete is floated. They often end up near the surface. The gap is from the normal shrinkage of concrete.

Originally Posted by Mark Reinmiller

The gap is from the normal shrinkage of concrete.

Mark,

You find that much shrinkage?

3/4"?

(1/4" are three joints = 3/4")

Originally Posted by Mark Reinmiller

Robert, you are entitled to your opinion, but it is a control joint formed with a plastic strip (as someone noted, Zipstrip is one brand). This strip has a top piece that is pulled off after the concrete is floated. They often end up near the surface. The gap is from the normal shrinkage of concrete.

ZipStrips They use them on pool deck surrounds in Quebec.

Normal shrinkage.
In my opinion No.
If that was the case the perimeter would also have a gap.
Concrete shrinks inward. All sides would be effected.

I suspect movement.

There is a deficiency somewhere.

Best regards Mark.

Originally Posted by Jerry Peck

Mark,

You find that much shrinkage?

3/4"?

(1/4" are three joints = 3/4")

Jerry, I see plenty of cracks that wide. I'm not sure if there are three joints. I think two are the same joint. Not sure about the third. In a basement slab that would not concern me at all. Around here I think it is routine practice to add water to the concrete so that it flows into place. It is not the proper thing to do, but common. Even in new construction it is not common to see any rebar or WWF in basement slabs here.

Originally Posted by Mark Reinmiller

I'm not sure if there are three joints. I think two are the same joint. Not sure about the third.

Mark,

From the original post "Found these cracks in 3 places in the basement floor."

In a basement slab that would not concern me at all. Around here I think it is routine practice to add water to the concrete so that it flows into place. It is not the proper thing to do, but common. Even in new construction it is not common to see any rebar or WWF in basement slabs here.

Well, adding a lot of water could do that, also would lead to weak slabs, thus so many crack control joints - makes sense in that light.