Cracks developing in garage slab

[chicane]

I have a new (5 months old) slab; approximately 25' X 30', 4" thick, 3500psi, wire mesh and fiber reinforced.

The slab was allowed to cure over a month before anything heavy was put on the floor.

About a 2 months ago a hairline crack developed near the middle of the floor. And now I see a new hairline crack appearing length-wise.

Needless to say I am not to happy about this.

Should this be something that I should be concerned about with the integrity of the floor or is it more of a cosmetic issue?

 

[Skinny_Blinky]

I have a new (5 months old) slab; approximately 25' X 30', 4" thick, 3500psi, wire mesh and fiber reinforced.

The slab was allowed to cure over a month before anything heavy was put on the floor.

About a 2 months ago a hairline crack developed near the middle of the floor. And now I see a new hairline crack appearing length-wise.

Needless to say I am not to happy about this.

Should this be something that I should be concerned about with the integrity of the floor or is it more of a cosmetic issue?

That is the one of two guarantees that you get with concrete. It WILL crack. It's up to the owner as to where one chooses to place the cracks with expansion joints. It's neither cosmetic (as it is there to stay) nor is the structural integrity compromised (it's there to stay).


This may be a stress crack (from your description) which is normally the full depth (or cross-section) of the slab, or it may be a surface shrinkage crack. Nonetheless, it's there to stay.

Wire mesh is basically useless. Fiber additives are to control surface shrinkage ONLY. It is not for any strength reinforcement. If someone told you otherwise, they were misinformed.

 

[brone1]

I was always told there are 2 kinds of concrete

1. Cracked concrete.

2. Soon to be cracked concrete.

 

[bmwpower]

No control joints? How was the sub-base?

 

[chicane]

No control joints? How was the sub-base?

No control joint. The soil is hard as a rock VA clay. I can't remember how many tons of gravel was laid for the base (but it was over 10 tons I believe) and it seemed well well pre-paired. There was a moisture barrier laid then the mesh then the fiber reinforced concrete.

I wanted to put a four post lift in there but I'm not sure if that will be a problem now.

 

[chicane]

Wire mesh is basically useless. Fiber additives are to control surface shrinkage ONLY. It is not for any strength reinforcement. If someone told you otherwise, they were misinformed.

If wire mesh is useless why is it required for the inspection process?

 

[Charles (in GA)]

Concrete will spend the next 50 years (aprox) hardening and shrinking. As it dries out, it shrinks, and thus cracks. It will crack where it wants to, if you saw cuts in it, or put in keyways or "expansion" joints, then it will tend to follow them most of the time.

If its done right, it won't crack much more than hairline, and won't shift and cause unevenness,

My slab took almost two years before the first crack appeared, but it has metal keyways that were set and most of the shrinkage followed the keys. When the hairline cracks showed up at the edges, they were at anchor bolts and Door track anchors that were set into the slab for a rolling door.

Charles

 

[mjohnson327]

Don't feel bad.My shop floor was poured in July and i have found a stress crack.
When i built my house and ordered my tile i ordered 4 extra cases ,because i was told to expect the stress cracks.

 

[Skinny_Blinky]

If wire mesh is useless why is it required for the inspection process?

Two different isues altogether. Inspection and structural design are apples and oranges. Not to mention how mesh is laid in and placed in the concrete.

I'll not argue this point. I know from experience and schooling.

No more fishing for me.

 

[chicane]

Concrete will spend the next 50 years (aprox) hardening and shrinking. As it dries out, it shrinks, and thus cracks. It will crack where it wants to, if you saw cuts in it, or put in keyways or "expansion" joints, then it will tend to follow them most of the time.

If its done right, it won't crack much more than hairline, and won't shift and cause unevenness,

My slab took almost two years before the first crack appeared, but it has metal keyways that were set and most of the shrinkage followed the keys. When the hairline cracks showed up at the edges, they were at anchor bolts and Door track anchors that were set into the slab for a rolling door.

Charles

What about doing something like cutting in an independent Sonotube footing supporting the lift independently of the slab?

 

[chicane]

No more fishing for me.

Did you catch anything?

 

[Vicegrip]

What about doing something like cutting in an independent Sonotube footing supporting the lift independently of the slab?

Why? The existing slab is up to the job at hand if it is the right thickness and material as called for by the lift maker. 4 post lifts are less dependent on the slab anyway. Some hairline cracks means nothing. My 24X30 slab is 4 to 6 inches of 3000 with both wire and rebar on rock hard VA soil too. It also has hairline cracks. They will not likely shift or grow wider as the rebar keeps things in line. Even with wire only your cracks are not likely to be a problem. You can saw cut and hope it takes the hint and cracks along the lines or let the slab crack itself where it wants to. Ether way your slab will have cracks in it.

 

[tdickman]

No control joint. The soil is hard as a rock VA clay.

Doesn't matter how hard the surface under the concrete is, the clay/soil and cement are two different materials with different coefficients of thermal expansion. Depending on the width and depths of the cracks, you may want to saw cut the floor about 25% of the slab thickness (if it doesn't interfere with the wire mesh) then fill the cracks and coat it....or just fill the cracks and coat it.

Here is floor I did, this job was a fire restoration project. Cracks were chased with a diamond tuck blade then filled with a polyurea, we then ground and feathered the crack area to create a smooth transition. Then coated. Its not perfect but it looks 100% better.

Before............

After Prep..............

After Coating was completed...........