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-   -   Cracks in new concrete (http://www.diychatroom.com/f105/cracks-new-concrete-186121/)

Contractor9 08-28-2013 07:50 PM

Cracks in new concrete
 
4 Attachment(s)
I just had 1400 sq feet of concrete patio done last month, with color concrete, stamped. The contractor did the work on a very hot day, and then when I asked him if I should spray water on the concrete, he said no.

We had 105+ days for a week right after that, and looks like the concrete has not cured well. Right away nearly half of the controlled joints had long cracks, and cracks started appearing (and getting longer) on the concrete surface (see the pictures).

It also seems like the top layer of the concrete is not very strong, as I dropped a screwdriver from 3 feet height and it chipped the concrete.

The contractor says this is normal (no surprise there :-)). Is that correct? He says he will put a quick patching, and once the concrete is sealed, the cracks won't be visible at all.

What do you guys think? Thanks for your advice.

jomama45 08-28-2013 10:31 PM

I think you contractor is full of BS, but that's just me. And I have no idea why he hasn't sealed the concrete yet, over a month in sweltering temps? What's he waiting for??

stadry 08-29-2013 07:23 PM

can we also suppose the check is already cash'd ? ? ?

Contractor9 08-29-2013 08:22 PM

Unfortunately, Yes :-(

Mort 09-01-2013 06:14 PM

Looks like he poured it rrrreeeeeaaaaaalllllyyyy wet. And I'm sure there's a tail-light warranty on it, eh? I wonder how he's planning on fixing that huge crack so you can't see it.

Let us know how it goes.

Tscarborough 09-02-2013 12:32 AM

Tear out and redo, correctly this time.

stadry 09-02-2013 05:27 AM

here's a thought,,, what about overlaying the existing ? certainly worth a few phone calls, isn't it ?

had you look'd at his work on other projects ? stamp'd conc isn't brain surgery however there're some necessary tasks to be done in the proper order at the right time or the job goes south,,, 1 of which is watch the temp incl winds,,, looks like you had some surface crusting & it was floated over,,, but that's just my opinion from here,,, good luck ! not easy putting up w/nagzilla's stares, is it :laughing:

Contractor9 09-09-2013 10:58 PM

Thanks for all the feedback!

I called the ready-mix concrete company my contractor had used, and inquired about what exactly was ordered by my contractor. It turns out that he ordered the concrete with a slump of 5, which is marginal at best (4 or less is desirable). So the concrete was already somewhat watery. On top of that, he added 40 gallons of water on arrival (to 16 cubic yards of concrete), making the slump to 7.5 - WAY too watery. The water to cement ratio was 0.59, making both the ratio as well as the slump too high to make acceptable concrete.

It turns out that he clearly violated the ASTM C 94 standard. According to the ready-mix quality control guy, he should have requested plasticizer instead of adding so much extra water. Plasticizers are cheap ($1-3 per cubic yard), so it is really surprising that he cut corners there.

Now I also understand why he asked me not to spray water, as he know he already had put in too much water to begin with. So we ended up with too much water during pouring, and too less water during curing.

Just to gather some conclusive evidence, I have asked the concrete quality control guy to come by tomorrow and do some Schmidt hammer testing, so that I can clearly show that the slab is weak. (For those who do not know this, the test is free, and non-destructive).

Then the fun will begin when I break this to the contractor...

Tscarborough 09-09-2013 11:05 PM

Don't get too excited until you read your contract. You do have one, right?

jomama45 09-10-2013 08:38 AM

I'm really surprised the ready mix supplier shared all of that info with you, unless you bought the concrete directly? Kind of sounds like they're willingly throwing the contractor under the bus. Makes me wonder if they have some other issues with him or something??

I think your best chance at remediation from the contractor is if you have a contract from him stating the proposed concrete mix strength, and it fails at the tests. I highly doubt that the contractor's contract states anything about allowable maximum w/c ratios or cracks.......

Contractor9 09-16-2013 03:17 PM

I have the Schmidt Hammer test results:

The compression strength of the patio ranged from just 1500 PSI to 2200 PSI. COmpare this to my existing patio right next to it, which scored 4000 to 4500 PSI.

As expected, the contractor is balking at the idea of redoing the work. His excuse is that everyone adds extra water into the concrete preparation, and 1500 PSI is just fine.

The work is clearly not acceptable to me, so let's see how we resolve this. I will keep you posted.

Thanks for your replies so far, I learned quite a bit already.

Contractor9 09-16-2013 03:44 PM

Quick question: The contractor now says he will overlay a top layer of strong bond concrete to make the concrete stronger. Is there such a thing?

Canarywood1 09-16-2013 06:59 PM

Like irc said you can try an overlay,just be aware that the cracks in the existing pour may telegraph.

joed 09-17-2013 10:12 AM

How thick a layer? The cracks will likely come through any layer put on top.

Fix'n it 09-17-2013 10:13 AM

post a pic from further back.


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