Cracks in new concrete slab?

Question

I just had a brand new 3 car garage built. The slab is a 4 inch slab, with monolithic footings. The ground seemed to be compact well with lots of gravel and the contractor used mesh during the poor. There were no stress cuts placed in the concrete, it was one solid pour. The slab looked great to me after it was finished. However, about the past month or so, I developed about 25 various cracks in the slab. Most started out as very think, barely noticeable cracks, but they all seem to be getting wider and longer. I can tell these cracks are likely to continue expanding. I know some cracking is normal, but when or how do you know if there are too many?

Answer 1

Concrete cracking is normal in some respects. As soil gets moist or dries out it expands and contracts. Expansion joints are put into concrete for just that reason; concrete is rigid.

A lot of the finshed product with concrete has to do with the temperature and humidity when it was poured and as it set up. Cool/damp conditions are best. Plenty of time to cure before use is important too.

For a garage floor I would have used something more than mesh though. Mesh is fast but not all that strong. I know it meets most standards but it will crack! Persoanlly, even though it would have cost more I would have put in rebar at about 12"X12"and maybe added a couple more inches of concrete.

Answer 2

crack will develop depending on the type of concrete used and many other conditions. If there is too much water in the mix when it is poured it will make cracking more likely. Curing time is best to be slow so a pour on a hot day will make the concrete dry too quickly and shrinkage will cause cracks to develop, ctually a concrete slab should be kept damp for at least a couple of days to allow a very slow cureing time, but when keeping it damp it should not be wetted and then alowed todry and then wetted again as this will change the moisture levels and this will cause cracking. Putting the slab under stress during curing will cause cracking, dont drive cars on it for a good week.
Cracks in a slab are normal as all of the above are difficult/impossible to control. A crack wider than 10mm would be considered a stuctural issue but anything smaller is only ugly to look at, but you chose to have no joints put in so you get that, in future if you dont want any joints done, make sure you get the slab cut with a concrete saw in the same way as a normal joint, you can get this done the same week you do the pour and later on fill it with silicone sealer, this allows for movement and helps to align cracks in the cut line.

Answer 3

this isn't normal, either the mix contained too much cement or dried too quicky and shrank. The mix should ideally have contained a plasticiser to slow the drying process, or the slab should have been sprayed with water when part-dried. If the concrete is also damp it would indicate that the layer of visqueen (plastic damp-proofing) is missing and the water in the concrete has gone downwards, speeding up the drying process. If the plastic was in place it would have retained all of the moisture, drying out slower As concrete hardens to a peak over a 40 year period this will get worse I would get a structural engineer to look at the damage before passing the report on to the builder. is the house still under warranty? if not you can still claim for shoddy workmanship. The concrete floor is not load-bearing and could be dug up and replaced without affecting any other part of the building

Answer 4

When I inspect concrete slabs and find cracks, the three basic things I look for are:

1. A crack wider than 3/8 inch.
2. A crack with vertical lift or shearing.
3. Previously repaired cracks that have re-opened.

I also look at the location and direction. For example, a crack that runs angled across a corner of the slab may mean that that corner is sinking.

I would get a third party out there to look at it for you and give you an opinion after actually looking at it.

You could also seal and fill the crack, then see if it re-opens or keep spreading.

Answer 5

This Site Might Help You.

RE:
Cracks in new concrete slab?
I just had a brand new 3 car garage built. The slab is a 4 inch slab, with monolithic footings. The ground seemed to be compact well with lots of gravel and the contractor used mesh during the poor. There were no stress cuts placed in the concrete, it was one solid pour. The slab looked great to me...

Answer 6

The concrete in your house is supposed to be 4 inches thick. The concrete in your driveway and garage is supposed to be 6 inches thick because of the extra weight it has to endure. That is what I learned in school here in Florida. It would make sense that it would be the same where you are. I would check it out. The slab might have to be torn up and redone. Good luck.

Answer 7

Concrete is a very unique material. When installed properly, it can be one of the most durable and long lasting products you can use around your home. However, many concrete contractors fail to follow established guidelines with respect to concrete placement. Durable, high strength, and crack resistant concrete does not happen by accident. You must do many things to achieve these qualities.

Concrete can crack for many reasons. Shrinkage is a primary cause of cracking. As concrete hardens and drys it shrinks. This is due to the loss, thru evaporation, of excess mixing water. Thus, in most cases, the wetter or soupier the concrete mix, the greater the shrinkage will be. Concrete slabs can shrink as much as 1/2 inch per 100 feet. The actual amount is 1/16th inch for every ten feet of horizontal distance. This shrinkage causes forces in the concrete which literally pull the slab apart. Cracks are the end result of these forces.

Concrete does not require much water to achieve maximum strength. In fact, a wide majority of concrete used in residential work, in many cases, has too much water. This water is added to make the concrete easier to install. It is a labor saving device. This excess water can not only promote cracking, it can severely weaken the concrete.

Also, rapid drying of the slab will significantly increase the possibility of cracking. The chemical reaction which causes concrete to go from the liquid or plastic state to a solid state requires water. This chemical reaction, or hydration, continues to occur for days and weeks after you pour the concrete. You can make sure that the necessary water is available for this reaction by adequately curing the slab. The use of liquid curing compounds, covering the slab with plastic, wet burlap, and other methods can be used to cure concrete.

Cracking can be minimized by following other guidelines as well. Install the proper strength concrete for your intended use. Concrete is available in many different strengths. The ground upon which the concrete will be placed must be compacted. Never pour concrete on frozen ground. Install adequate control and isolation joints. Control joints occur at regular intervals in the slab and are intended to account for horizontal and vertical movement in slabs. These joints can be formed with a tool or sawcut soon after the slab has hardened. The purpose of these joints is to create a zone of weakness where the forces which are pulling on the slab will relieve themselves. Isolation joints allow a slab to move independently of other fixed or stationary objects.

As a last resort, consider installing reinforcing steel. Reinforcing steel for residential purposes comes in two basic varieties, wire mesh or rigid reinforcing bars (rebars). The use of reinforcing steel can help in the event a crack develops. The steel can often stop the crack from widening and displacing vertically. Reinforcing steel is also quite inexpensive. It is usually very easy to properly install. Steel can significantly enhance the strength and durability of concrete. In addition to all of the other measures taken to prevent concrete from cracking, steel offers a low cost last line of defense.

Answer 8

Why Does Concrete Crack

Answer 9

The concrete slab might have been laid in a uneven surface or the curing to the slab is not good.

Answer 10

I'd pay a home inspector from your area to check it out. They'd know what is normal or not for your area. It depends a lot on temperature ranges, humidity when pouring/setting, and the ground underneath.