Does your floor have cracks?

[jrhaines2]

Just curious if your concrete floor has any cracks in it.I have poured a few floors but I am a novice and far from a seasoned concrete contractor and all the floors I have poured or helped pour have ended up with cracks.

Not that I check out every concrete floor I come in contact with,but I have never observed a floor with no cracks in it.

 

[NXGTS]

I just had a new floor poured this spring. Yes, it has cracks and was warned it might because it was a little breezy the day of the poor.

 

[2manytoyz]

All concrete cracks in FL. Probably due to the sandy soil. House foundation, driveway, sidewalks, etc. "Hopefully" they'll crack along the lines that are scored in the surface... but usually crack in many places.

Your location may differ, but never seen an uncracked concrete slab here.

 

[Gary S]

My garage floor has a crack along every relief cut I made when the concrete was fresh. It worked just like intended.

 

[dirttracker18]

Very minor crack (hairline about 6") under the service door where the concrete protruded over the foam board.

Other than that, nothing in a 30 X 36 with no relief cuts.

 

[Will67]

Got lots of em, you need some concrete cracks?

My suggestion is to do the maximum amount of prep work...compact and compact then compact some more.

 

[rvr6000]

I rebuilt my garage about five years ago.....my buddy who did the cement work tore out the old slab, dug it out and packed down all new class 5 before pouring the new slab. Within a couple years the floor had a crack almost identical to the one I had in the original floor. Wonder if there isn't a really soft spot or something several feet down in that area.

 

[Al Bundy]

My floor has none but my **** has a crack in it.

 

[pro machine Engineering]

mine has cracks none that spread open wide. i got 6 inch pad poured been here 15 years has a bridgeport southbend lathe 2 cnc machines and a vibra burr with no problems the cracks was there before got the cnc machines in

 

[Falcon67]

Mine has spider cracks and the slab next door has that too. The new house to the west has dyed and sculptured concrete - looks nice and has some bigger cracks than my garage floor. We also have some in the driveway, on the side walk, etc.

 

[ddawg16]

I have a couple of hairline cracks.....you have to look hard to see them...but they are there.

But I'm not concerned....I know it's thick enough and has enough rebar.

 

[Jazz]

My garage floor is about 25 years old, 24'x26' and not a single crack on the entire slab. Guessing its a combination of a good pour and stable ground.

 

[bobadame]

I was in the local Homer Depot yesterday and I noticed their floor had no cracks. It had been cut on a grid maybe 12' X about 16'. I imagine it's also pretty thick. My floor is 4" to 6" thick with 6"X6" 10 gauge steel mesh. It's been in place 3 years now and it's starting to crack. Under the concrete is many tons of compacted #7 structural fill. Under that is expansive soil. It was just a matter of time. Unless you've got HD's money to pay for extra thick high strength concrete, at least around here, it's going to crack.

 

[buening]

Cracks have many different sources/causes. Some are temperature shrinkage/expansion cracks, plastic shrinkage cracks, some are due to improper compaction of the aggregate below (settlement), some over time will develop if you don't have your downspouts positioned away from the building (washes away fines in subbase and then settles), there are also cracks associated with a chemical reaction called alkali-silica reaction (ASR), and many more. You can also have surface crazing/map cracking that is sometimes due to too much water on the surface when finishing.

I recommend going a bit overboard on the amount of rebar a person puts in the slab, pour the slab on a day that is not windy and not too hot, steal the water hose from the finishers so that they don't make it too soupy (easier for them to finish) but ends up crazing the surface, practice proper curing methods, and put a bit more aggregate below the base and compact it with a machine tamper. Footings down to the frost level are also highly recommended but be sure the slab is floating. If you really want to go overboard, you can have shrinkage reducing admixtures put in the concrete to make it a low shrinkage mix. That stuff isn't exactly cheap and is commonly used in warehouses where control joints are kept at a bare minimum and cracks are not allowed.

Some good info to help understand cracking and ways to avoid it:


http://nrmca.org/aboutconcrete/cips/03p.pdf
http://nrmca.org/aboutconcrete/cips/04p.pdf
http://nrmca.org/aboutconcrete/cips/05p.pdf

List of all the helpful documents: http://nrmca.org/aboutconcrete/cips/

 

[c39er]

My 15 year old floor had no cracks-till the last earthquake-now I have a 4 foot long very thin crack. Never has extended. 6" thick with fiber and 6" wire mesh and zip strips in 12 foot grids.

 

[Zeke]

So many that I have to get out of my rolling office chair and lift it to move it.

House and garage built in 1930 on expansive soil.

 

[InPrimer]

I have about 1500sq' of garage, another 2000sq" of dryway parking area. The concrete guys guaranteed 3 things, 1 you"ll get cracks, 2 it won't catch fire, and 3 no one is goint to steal it. My point, unless the cracks are structual there is no real way to prevent it.,

 

[pro machine Engineering]

I know wal-mart does it and I bet the other big stores do also. When they built the 3 new super centers for walmart in the area. All 3 of them did not pour the floor until the airconditioning was installed and they could cool the inside of the building when they poured. They use a high grade of concrete and cooling things down makes it cure slower helping with cracking. I havent noticed any cracks in the walmart floors

 

[ket-tek]

I have two hairline cracks right down the middle in a 28x38 6" fiber 3500psi floor with 2 relief cuts. The cuts stopped the cracks. You can see the cracks but you can't really feel it or put put anything in it. It did not raise or spread apart, I barely notice it.

 

[hemibee69]

An old concrete guy told me "there are 2 kinds of concrete, concrete with cracks and concrete about to crack"

 

[cowboyjosh]

My garage floor is epoxied, but before i had the floor done the control joints cracked, but nary a hair line crack in th slabs. I have a couple hairline cracks in my sidewalk and back patio, and nothing more then cracks in the control joints in the basment floor.

 

[c39er]

Who really cares as long as the cracks don't open up a 1/4"?

 

[NUTTSGT]

Yep, mine has cracks, they're right in the relief cuts.

 

[KermitFrog]

Mine has a crack going all the way across my garage. It is around 37' in on the slab. The idiot that poured the slab knew nothing about concrete - that being said I did learn from my mistake. When I was getting it all ready I used a lot of clay, just because of the sand....of course the lot not being level was a player in it too. One side was built up almost a foot while the other maybe 4 inches. I do think the clay has helped the slab from cracking worse. Of course as I said before, I'm an idiot when it comes to concrete.

 

[StaggeringGoat]

My 40x60 has releif cuts in 10x10 squares throughout, there are no cracks that I am aware of, unless they're in the cuts. I don't know how thick it is but it's a commercial building so I'm guessing it's a bit thicker than normal.

 

[ConCretin]

An old concrete guy told me "there are 2 kinds of concrete, concrete with cracks and concrete about to crack"

No offense hemibee69, but I propose that we all agree to never post that particular expression ever again.

 

[hemibee69]

No offense hemibee69, but I propose that we all agree to never post that particular expression ever again.

How about this one...."the truth hurts"

 

[radrush]

An old concrete guy told me "there are 2 kinds of concrete, concrete with cracks and concrete about to crack"

When contractors say this it's their way of telling you that they are lazy slugs, that they understand nothing about concrete, and that they have never even read the information put out by their own trade association.

List of all the helpful documents: http://nrmca.org/aboutconcrete/cips/

 

[Dan in Pasadena]

Not trying to start an argument but you're in err about this opinion. Concrete DOES crack. It all cracks which is why concrete is placed with crack control joints in designed-in locations on large civil projects.

I am the Project Quality Manager for Metro here in L.A. I am currently working the Sepulveda Pass Widening project ("Carmageddon", you've heard of us) I have over 30 years experience in huge scale civil engineering projects. I did the Metro Green Line, the Eastside Extension and many more.

Concrete cracks. The question isn't whether it will or not, the question is how to control it. It cracks in approximate squares and for example on the project I am currently working the Design-Builder is required to use Caltrans mix designs which have high water to cement ratios and are slightly more prone to cracking which necessitates different curing methods to minimize it.

 

[Dan in Pasadena]

Back to the OP's question:

My cracks have annoying floor between them!!!

My garage slab is 85 years old and unlike modern residential construction, there is no perimeter footing, so no way to demo and replace the slab. What I've done is make a relief cut in the slab intending to demo the most heaved portion, repour and then tile ala Jack Olsen which will allow me to fudge a bit with the thinset and make my floor approximately flat. Pretty much the best I can do.

My floor has two oil change pits in it that the prior owner filled/paved in 1959. Decades ago, water undermined the slab on one side and the slab cracked to the limit of one of the pits. You can see the pit edges and the relief cut in one of the photos below:

Opinions and comments about alternate ways of dealing with this are appreciated.

 

[rvr6000]

Can't say I know a whole lot about concrete.....what role does wind play when pouring concrete? Dries too fast?

 

[ConCretin]

Can't say I know a whole lot about concrete.....what role does wind play when pouring concrete? Dries too fast?

Wind tends to dry out the surface before the concrete underneath has set up enough to support the weight of the finishing crew. The concrete 'crust' on the top cracks resulting in crazing.

The worst case scenario is de lamination of the slab surface.

Evaporation retarders like Confilm help a little but the best solution is to shield the slab from sun and wind with windbreaks, etc. or pick a different day to pour.

 

[ConCretin]

How about this one...."the truth hurts"

I was just being a smart ***. Someone inevitably throws that expression in to every thread on the issue.

It's entirely possible to place an average size garage floor without cracks.

 

[jtshusker]

where I live you can't pour concrete without cracks, bentonite in the soil. No matter what you do it cracks at every house in my neighboorhood!

 

[jtshusker]

see if you have bentonite in your soil where your live. I am not sure on the spelling of bentonite, but look it up. Do your neighboors have the same problem?

 

[jrhaines2]

When contractors say this it's their way of telling you that they are lazy slugs, that they understand nothing about concrete, and that they have never even read the information put out by their own trade association.

List of all the helpful documents: http://nrmca.org/aboutconcrete/cips/

When contractors tell you concrete cracks,it is there way of telling you that they are not in fairy land.

Please present me with one contractor who will guarantee a floor with no cracks???

Does your floor have cracks?

 

[buzz4041]

Two things for sure concrete will do 1. Get Hard 2. Crack

 

[dirttracker18]

I totally disagree with the statement that concrete will crack. Over a very long term I suppose it is inevitable but in the lifespan of a typical garage no. Unless there are circumstances that cannot be controlled there is no reason why concrete must crack. If your contractor tells you that your concrete MUST crack, find a better concrete guy.

For our resident project manage, I am sure in large scale pours there are issues that are assumed but in a small scale foot print of the average garage, the possibilities can be minimized.

If it was not for extending the concrete over my foam at the service door (about 1" thick), I would have NO cracks at all. That one crack is minimal and barely noticable.

I would not expect any contractor to gaurantee no cracks but a good one can do it most of the time on small scale jobs.

 

[buening]

I totally disagree with the statement that concrete will crack. If your contractor tells you that your concrete MUST crack, find a better concrete guy.


I would not expect any contractor to gaurantee no cracks but a good one can do it most of the time on small scale jobs.

+1! There are many jobs where the Contractor has to guarantee no cracks (larger warehouses). You won't find many that will guarantee a small slab though due to the small profit margin. A good quality concrete contractor can provide a small slab like a garage that will not crack.

 

[dirttracker18]

Yup,

In my area where major industry is building, many pads and pours must be crack free for safety.

Cracks appear, contractor must remove, repair and replace.