Slab Cracks in New Home

I need some help from a Pro.

We recently moved in to our new home a few months ago. We had noticed slab cracking before we moved in but were assured by the builder that this was a normal occurance and they would repair the cracks before we moved in. The problem now is the cracks are showing up through our vinyl flooring. The slab was poured December of last year so I would assume there may be some settling still occurring right now. I am worried, however, that these cracks will continue to grow and pose problems with termites and mold later on. The home is under warranty and would like to know what steps, if any, I should take. Please take a look at the following URL's at some pictures I took in June. Any feedback would be welcome right now. Additionally, if you could tell me what caused these cracks I would be thankful.

http://nexus.nanospace.com/~phorse/famroom.jpg

http://nexus.nanospace.com/~phorse/livingroom.jpg

Regards,
Tony

 

[JAE]

Looks like shrinkage cracks to me. Note that in your family room, the crack at right extends from a re-entrant corner. Many homebuilders and their crews like to place concrete with a lot of water. The soupier the mix, the easier it is to finish. The excess water in the mix adds to shrinkage and the resulting cracks.

Since your slab is about a year old, probably 70% to 80% of the total anticipated shrinkage has occurred. I would definitely fill the cracks with a semi-rigid epoxy. (moisture, etc are valid concerns) Each crack should be routed out to form a V shape groove along the crack. The epoxy can then be placed in the groove. Some people prefer to form a more rectangular groove, perhaps 1/2" to 3/4" wide and 1/4" deep. Some tape is placed across the bottom of the groove and the epoxy installed such that it only attaches to the vertical sides of the groove. This allows the epoxy to stretch across the full width should future movements occur.

 

[ishvaaag]

I would also recommend to anyone this reading to use slabs on the ground at least 15 cm thick (preferably 20 cm) and doubly reinforced top and bottom. Both the shrinkage and mechanical strength problems will be far less than with one 11.5 cm thick weakly reinforced. Of course it will cost a bit more but, are worth the savings the problems phorse tells us about?

The pattern indicates clearly shrinkage, but more inspection would be welcome to definitely ensure there's no settlement influence (mainly in the form of a too thin slab).

 

[JAE]

Well, for homes, I don't think 15 cm (6 inches) is appropriate. Most homes in the U.S., with slab-on-grade foundations, use 10cm (4 in.) slabs and perform very well. Reinforcing in the slabs in non-epansive clay regions can actually be eliminated if you substitute fiber reinforcing. Otherwise, #4 @ 18" o.c. (13cm dia @ 450 mm o.c.) would work fine.

In expansive clay regions, the use of stiffened slabs with turn-down grade beams, monolithic with the slab are used. Still, the slab is usually 4". The thickness of the slab doesn't directly affect the cracking that Tony is talking about.

 

[ishvaaag]

It is clear from what in this site read and some UK books I have the practice in UK and US is less thick for both walls and non load bearing slabs on the ground. For mats bearing loads the difference must be not much, nor must be in prefab walls and so on.

The fiber reinforced option I maybe would look positively on well compacted ground, the other I wouldn't feel so happy with. For instance, it is unusual for us there having anything non reinforced at separations bigger than twice the thickness, which this does not meet. On the other hand, steel ratio looks first-sight enough for anything related with centered efforts, but I am not confident in such being the efforts in any slab on the ground. Yet I take your word, and the many 11 cm or so examples seen be there for something.

I think that the general scope of soils is not much different between continents, in spite of some cautions in some books I have on foundations...soils will be poor, normal or good and so on anywhere, and exceptions need be treated as so.

 

Thanks for your responses to my concerns.

Do you think I should I hire a structural engineer to inspect the foundation? Also, I am assuming the only way to truly inspect all the slab is to rip up the carpet and vinyl? I wouldn't be too concerned if the cracks were not all the way through the slab but from the size and patterns of the cracks I would think that some of them may be all the way through which could pose great problems later. I value all of your opinions and advice.

Thanks,
Tony

 

[rustbuster1]

You might want to get the builder to recognize his obligation here. Most new home either have an explicit warranty that is violated here, or are covered by standard commercial terms which ascribe a 12 month "warranty". If you send thim a registered letter defining your concerns, you will at least have initiated the claim at a verifiable point in time. Then you and he can mutually negotiate such items as which structural engineer to use if one is needed and who will pay for what. This should give you reasonable protection in case you have to pay for your own services in assessment and remediation, should the builder prove unresponsive.
Thinking ahead, be advised too that many states require - under legal penalty - that all defects in homes be revealed to the buyer, so your choosing to live with this may come back to haunt you later if you want to sell.

 

[Ron]

Tony,
JAE has appropriately described both the cause of your problem and its repair. The problem is non-structural so it really isn't necessary to hire a structural engineer to evaluate the issue, but moreso as Rustbuster1 has said to get the contractor to recognize his responsibility.

I would encourage you to go on record immediately by notifying the contractor by certified mail that the shrinkage cracks are excessive and intolerable.

As JAE mentioned, you likely have achieved the most significant shrinkage already, but the remainder will open the cracks a bit more and can present a problem for materials bonded to the surface (tile, fully adhered vinyl, etc.).

 

Thanks ALL..

The builder is already aware of my issues and I am unsure at this point how far they will go to correct the problem. We chose a type of vinyl which looks like wood "Congoleum Forum Plan" in our kitchen and family room. It is glued down to the slab in 3 x 36 slats. The problem with this flooring as with any other vinyl is it is showing all kinds of cracks across the slab. The builder wanted to remedy the problem by placing a free floating floor down such as a wood laminate (largely at my expense) on top of the vinyl. They tried to tell me that they would not repair any cracks unless they were greater than 1/8". This does nothing to fix the root of the problem or the other cracks which are hidden under the carpet.

Luckily I videotaped our walk through with the builder and their representative assured me the slab had been inspected before flooring was put down and any cracks would have been repaired before the flooring was affixed. I honestly have no idea if any such repair took place but for some reason I highly doubt anything was done. I am hoping that the pictures and video tape footage of the cracks as well as the statement from the builder (recorded) will solidify my case. I am almost sure if I have this problem then many others in the same tract might also have the same issues but might not even know if they didn't catch it before the carpeting was put down.

Oh well, from my point of view, I do not feel like I am overreacting. When you pay so much money for a new home these days, you would expect it to be mostly trouble free.

We shall see how this plays out but in my mind they should rip up all the flooring and properly repair the slab.

Thanks again everybody for your expert comments!

Tony