Help, Dreaded cracks how bad will they get, what to do?

[davidhalliday]

I have just spent my life savings redoing the pool deck and patio with stamped concrete. But now after a week and one day it is cracking (not allong the control joints.) Today I have read lots on concrete and the threads here.

The cracks are not very wide at the moment but do traverse the thickness of the slab (can be seen at the edges) and run in random across the slabs. There are currently about 5 or 6 spaced over the work area.

The concrete was layed on a compacted base rock, with a rebar grid, I am concerned that the grid was not pulled up into the slab. I am also concerned about the control joints, maybe these are not cut deap enough and that the concrete was to wet or a poor mix.

What can I do? As this is over a week from the pour I have paid the contractor, what options are open to me? Will the cracks get worse?

I will try and post some photo's if this will help.

Thanks.

 

[SCGeo]

I assume you were not present at the time of placement, which presents a problem.

Some questions for you.

You mention a stone subbase, but was a vapor barrier installed between the stone and slab? That would be more important in my mind than whether grid, which is not universally required in all cases, was used.

Were the joints cut the same day the slab was placed? Timing is critical in that department.

One recommendation I would make is to try and obtain the concrete tickets for your pour. They would provide some information that could be useful to start out.

Next, see if you can get a friend of yours who is a civil or structural engineer to take a look at the deck as a favor. Such a person could definitely provide you with a recommendation.

If nothing else, observe the cracks on a day to day basis and try to determine whether they are getting wider, and if not, sealing may be your best course of action.

If all else fails, one course of action could be to hire a local testing company to core the slab in 2-3 locations. A visual observation of the cores could provide insight as to the condition of the mix, for instance if the aggregate had segregated or large voids were present. The compressive strength of the mix could be tested as well.
You could also determine whether a vapor barrier was installed, and the stone and soil subgrade could be tested at the same time.

If you mean to bring suit against the contractor, I believe the last option would probably be necessary.

 

[davidhalliday]

SCGeo, thanks for the quick response, as it happens I was there, this was a week last Saturday, but I am no concrete expert.

The base was a layer of class 2 baserock compacted with a vibration compactor, there was no vapor barrier put down but the contractor soaked the area with water the day before the pour.

The joints were placed in the slab with a joint tool as the surface was leveled but before the stampwork was done with a joint tool in the damnp concrete. (Could the stamp process have filled in the joints? They dont seem to be that deep.)

Until yesterday (day 9 after pour) there were no visible cracks but now there are several.

The mix did seem very wet to me, the crew seemed to simply push the mix around using their boots. (this is also why I am concerned that the rebar would have been pushed right to the bottom with all these people walking over it.)

Finally, how do I find a local testing lab, I have tried yellow pages and web but I am not sure what to look for, I am in the San Jose area.

Thanks again.

Dave.

 

[Tryan]

It is my opinion that a vapour barrier actually contributes to cracking, the same as an overly wet subgrade would!Let me try to qualify! As you have already read other threads on this subject, I won't rehash too much, but I do find SCGeo's assessment interesting to say the least!If the contractor doesn,t get it right on the day then no amount of cutting, even if you bog the machine in the wet concrete cutting the control joints, will stop THOSE cracks!They are not occurring because of the normal expansion and contraction of a concrete slab, they are caused by the bottom of the slab being in an expanded state and the top shrinking prematurely! The only way to stop this happening is to equalise the moisture loss between the top and the bottom of the slab ON THE DAY. This can be done in different ways which have been discussed before,but basically it's the contractors fault, he didn't make the right calls on the day!You should talk to him to at least find out how he feels, and go from there! let us know.

 

[davidhalliday]

Today I talked to the contractor and he says that the cracks are not his problem and suggests I drill some holes along the cracks, go to home depot to get some epoxy and pump it in the cracks and all should be good. He also says he can give me the name and number for a guy that can do this for $300 if I like. Would this even work? At the moment the cracks are still very narrow, maybe 1mm or so.

As suggested in another thread I took a close look at the control joints. All are <1/2" deep some only just over 1/4", I also noticed that one of the cracks formed above a pool pluming pipe where no control joint was placed above it.

I am starting to get a sinking feeling about all of this. I now realy wish I had not paid up the last of the 11K so quickly.


Dave.

 

[SacreBleu]

Try the State Contractor's Licensing Board. Lodge a complaint there. It may not be successful, but at least it won't cost you anything to try.
Hiring a lawyer could well cost you far more than repairing the slab.

 

[SacreBleu]

postscript - many authorities consider any crack less than 1/8" to be "cosmetic", and not worthy of litigation.

 

[dbuzz]

The appearance of the cracks a week or so after the concrete pour rules out plastic settlement and plastic shrinkage cracking, which usually appear between 30 minutes and six hours post-pour. The timing may indicate craze cracking, a primarily cause of which is over-trowelling, a secondary cause is inadequate curing and a contributing cause can be the concrete mix (if there was a high water-cement ratio combined with a cement-rich mix).

However, you mention two things that stand out to me: "the mix did seem very wet to me"; and "the crew seemed to simply push the mix around using their boots". The Contractor's practice of pushing the fresh concrete around with their boots seems inconsistent with good practice. Did they vibrate, float and trowel the concrete?

It seems to me that the most likely explanation for the cracks is subsidence cracking, which is caused by high water content ("the mix did seem very wet to me"), too rapid placement and insufficient vibration ("the crew seemed to simply push the mix around using their boots").

If you think you're headed for the courts, get and a Professional Engineer involved ASAP and take plenty of photos including close-ups of the cracks (make sure you include a ruler or tape in the shot to establish the scale in the printed photos).

 

[JAE]

dbuzz is on track - I would add that in addition - smaller coarse aggregate can also add to the shrinkage of wet concrete and a shallow trowelled joint doesn't always get deep enough to force the crack to begin at the joint.

All concrete cracks to some extent - but with the rebar or mesh stomped on - its probably on the ground/concrete interface and isn't helping a bit.