New Slab....tons of problems

[Nitrobob]

Had my slab poured today for my 30 x 40. Contractor called me and said the concrete delivered was air entrained although he specifically told them what he wanted. Concrete provider acknowledges this and has taken full responsibility for the pour.

They have offered 2 things:
1) provide concrete/labor charges to pour another 4" slab on top of this one.
2) cut out all the bad areas completely and patch these areas with new pour
then epoxy coat the whole floor (no charge). Also refund all money for
first pour.

Concrete looks pretty bad...Lots of blistering that will defiantly delaminate and pop. Also quite a few areas of scaling. What is the best course of action here. Going another 4 in. wont affect build at all, no framing done yet.

Never heard of pouring a slab on top of another. Is this going to be a quality repair or a band-aid.

Any help is greatly appreciated.

 

[JJThrasher]

My opinion, cut it all out and start over.

 

[mopar440_6]

My question is, if the contractor knew the concrete mix was air entrained why did they continue to complete the pour?

I would push to have it all broken out and start from the beginning.

 

[red]

What's your concrete contractor say?

 

[ddawg16]

I'd go with the 4" on top.

The existing slab would make for a pretty good base.

And...knowing how some people like to pour slabs at grade level, getting the slab up away from grade is a plus

 

[jhelrey]

Pics?

 

[Nitrobob]

My question is, if the contractor knew the concrete mix was air entrained why did they continue to complete the pour?

I would push to have it all broken out and start from the beginning.

He didn't realize it till he started to machine trowel it. He also said he was asked when he ordered if he wanted it and declined but the sent it anyway. Not knowing he thought he was using regular mix because that what was ordered and on the ticket but after he called concrete supplier apparently the ticket was wrong and air entrained was sent.

 

[ssdave]

Air entrainment shouldn't cause the problems you describe, unless it was extremely high content. There may be something else wrong with the mix.

Personally, I think I'd go with another 4 inches over the top. That would be the fastest/easiest, and get the best product in the end, compared to a patch job. Whatever was wrong with the concrete to cause it to delaminate and blister in spots is wrong with the rest of it also, so the patch job will leave a lot of bad concrete there to fail.

As said before, the strength of the extra concrete is a plus if you top it with another slab. What will happen, is the concrete on top will crack easier and more. The first slab will also act like a vapor barrier, so plastic shrinkage cracking and slab curling in the top slab will be a concern. I'd place the new slab at as low a water content as I could, and do it on a cool, overcast day so that the top doesn't dry out quickly. That will help minimize plastic shrinkage cracking since the top won't dewater as quickly. Since the bottom slab it is placed on provides very low friction to help resist shrinkage, the slab will crack on a much smaller grid than a slab placed on a rough gravel base. I'd saw cut it at 10 foot intervals instead of the usual 20 ft because of that. Or, add microfiber to the mix, and don't saw cut it at all, and seal the surface after it cracks. Unless the appearance of it bothers you, I think that microfiber and no saw cuts would give you the best product overall.

So, my opinion summarized? The double slab will get you the strongest slab, but not necessarily the best looking one. If you want the best appearance, the only real way to go is to demo out the first slab, and start over.

 

[ford33]

Why accept substandard product? It is not what was designed or requested. Remove the existing slab and have them do it again with right product.

 

[Cairo94507]

Have it removed while it is still green and have it poured over.

 

[James-W]

I have mixed thoughts about it. At first I thought it would be best to rip it out and start over again. But now I am thinking a good case can be made for covering it over with new concrete. At the moment I am not real sure what I would do if it were mine.

 

[USAFpj]

If you pour over the 'troubled' slab with another 4in, will the contractor give you any type of warranty on the overall slab? I would see what his recommendation is, because if he cares, his name and reputation is on this decision.

 

[DougWil]

Very easy to get blisters power troweling air entrained concrete, easy to do hand troweling if you steel trowel it too soon.

What does this current slab have for reinforcement?
And what would the upper slab have?

 

[strutaeng]

I have researched about this topic. In general, the the industry consensus is that air entrained concrete is not to be hard troweled. The biggest thing is that air entrainement hampers bleeding of water, fooling finishers into thinking that they can proceed with troweling.

What was the air content? What they should have done is delayed the troweling.

If I were you, I'd rather pour another layer on top, even a topping slab will probably work. They make products specifically for this. Of course, assuming everything else still works (anchor bolts are still long enough, brick ledges, whatever.)

Good Luck!

 

[Chuck Baggs]

It's a tough call. If they used rebar, then demo will be more challenging, but if the mix supplier is paying, then start from scratch and demo out the old and re-pour. However, if the mix supplier is only going give you more concrete, then pout slab over slab with the mix you originally wanted.

 

[machsnell]

I would worry about the first slab reflecting cracks through to the new upper slab.

Tough one.

Sent from my SM-G900V using Tapatalk

 

[1940_dodge]

Sounds like the safest bet is to do it over from scratch but that didn't seem like a possibility.

 

[gnpenning]

It is my understanding that anytime you pour over existing slabs to put a layer of sand in between to keep cracks and defects from the bottom slab happening in the top slab.

 

[nh_yota]

I'm not sure I would go with the more complicated option because they could always screw it up a second time.

 

[Blk88GT]

I'd like to see a picture if you've got one.

Me personally, I'd have the whole thing removed and repour.

 

[sberry]

I would toss some rods down on it, pour over top, why toss it? Its a super base, pout on it and take a hook and pull rods up in the mix or set them on some bricks or chairs.

 

[lakeroadster]

Depends on where ya live Nitrobob.

If you live where freezing is common place I'd be concerned with water getting between the slabs during freezing weather and having frost heave issues.

Pic's would be helpful. Are the columns/posts already in the ground and cut to length? If so you just lost 4" of ceiling height if they double up....

I think I'd have them tear it out and do it right.

 

[hemifalcon]

nothing good ever lasts covering something of poor quality.. I don't know anything about concrete, but covering the bad concrete with another slab only sounds like a bad idea--logically. I'd have them remove the slab, and put down another one--no questions whatsoever..

 

[jask]

OUCH!! sorry for your troubles NitroBob. I would have a good look at those offers myself- we all make mistakes and the fact that they admit and are willing to make right is a good place to start. The slab you have is not structurally inferior and there are a lot of good reasons to use that mix in cold climates, but hard troweling is a recipe for surface defects and I personally would have no problem with either of those solutions offered.. IF... my plans did not include things like a two post lift or a really heavy point load ( big mills or lathes ) those can still be options but will need to be planned for now. If you pour a slab over it needs to be decoupled from the original pour with plastic or tarpaper etc and properly reinforced with fibers or welded mesh. Is this going to create problems with interior finished heights, stairs, doors etc? is it a slab on grade? or a stem wall?
I personally would be considering how much it would cost to add radiant lines to that topping slab

 

[Jon_E]

I had a slab for my 24x36 garage poured this morning by a crew who's been in the concrete business for over thirty years. I specified 4000 psi mix, 5% air entrainment, and nylon (short) fiber additive and they had no issues with it. It is a full 6" thick slab with 6-gauge mesh and radiant tubing. Concrete was started at 8 am, in place by 9:30 am and bull floated smooth by 10. The lead man is still out there now at 5 pm doing his third pass with the power trowel, and he expects to be here until at least 8 pm. I questioned him quite a bit today, to educate myself, and he said that the key to finishing a heavy slab with air entrainment is to wait it out.

I suspect that your contractor finished it off too early. Air entrained concrete needs time to cure and a light touch on the troweling.

EDIT: After asking my concrete guy about this very thread, he replied that the best thing to do is to tear it out and start over. He also said that if some sort of separation can be made between the old slab and a new slab poured on top, such as a layer of crushed stone or foam board, the old slab could be left in place (but not recommended).

 

[Jinks]

Long answer....... When I built this house I had a patio slab that I had poured myself. It was fine. The concrete sub misread the plans & cut it in half... He replaced it, but he wasn't any better at slabs than he was at reading plans. I had to have the patio & front porch jack hammered out & re-poured. The new concrete sub was as bad as the first, so the contractor jack hammered the front porch again & got a third sub to pour it correctly. Before the finish of the build I had patio cracks, so the third (& best) sub covered it with a second slab (we had room). Fast forward a couple of years & the whole thing is cracked again!...

This time, on my dime, I had it jack hammered again & poured by a good concrete contractor. It's fine & has been fine for 5 or 6 years. Moral of the story; Do it right the first time! Don't pour/patch over a bad job! You'll just get to do it again & again till you get it right.

 

[PT Doc]

Do it right the first time, so start from scratch and forget about it.

 

[tlmartin84]

WOAH..............

Do you not want it coated with something? The blistering probably is less than an 1/8" deep??? am I right?

If so you should look at having them bring in a grinder, and then coating it for you......probably be cheaper, and you get a coated floor..........

Most epoxy, and sealer preps recommend grinding. As far as the air being added, it won't affect the performance as a whole. Just as someone else mentioned, it is just the blisters from being trowelled before the air released, and it pushing through.

Just my 2 cents........

 

[joes169]

We use full (5-6%) air entrainment on almost every slab we pour, and we power trowel it. I understand some contractors struggle with it, but the OP's should have been able to use some kind of finishing aid to counter the air in the load.......

 

[Dominico]

Do it right the first time, so start from scratch and forget about it.

X2...X2....X2..DO IT RIGHT THE FIRST TIME!!!

 

[mygarageone]

Off subject but what causes a concrete slab to have hole pops in it year after year ? I have heard it's from the wrong stone being used in the concrete.

 

[HemiRamOn22s]

The cracks will transfer through. I would cover the slab in 2-3" of sand and pour a new slab. but thats 6-7" of ceiling height lost. Let me ask you this... was it windy when they poured the slab?

 

[ssdave]

Off subject but what causes a concrete slab to have hole pops in it year after year ? I have heard it's from the wrong stone being used in the concrete.

Probably an alkali/aggregate reaction; this causes some of the sensitive aggregates to react and swell up, popping a hole out where the aggregate was.

No cure for that particular problem, although sealing the concrete to keep moisture out helps.

 

[joes169]

Probably an alkali/aggregate reaction; this causes some of the sensitive aggregates to react and swell up, popping a hole out where the aggregate was.

No cure for that particular problem, although sealing the concrete to keep moisture out helps.

More than likely, it was from porous stones in the mix that act similar to sponges. They are more absorbant than common, and store water in Fall & Winter, and pop when it freezes. here, in my locale, chert is the most common stone to do such a thing, and chert pops are evidenced by observing a soft, chalky stone left right below the pop.........

 

[Nitrobob]

Just wanted to update this post.. Everything worked out...Concrete supplier paid to have it removed and supplied concrete for new pour free of charge.. Garage and floor turned out great...

 

[James-W]

Just wanted to update this post.. Everything worked out...Concrete supplier paid to have it removed and supplied concrete for new pour free of charge.. Garage and floor turned out great...

All is well that ends well.

 

[HemiRamOn22s]

glad to hear!

 

[lakeroadster]

That's good to hear. One less thing for you to have to wonder about.

 

[Todd.Brock]

Nice that they stood up behind their product. Glad it worked out

 

[James-W]

Nice that they stood up behind their product. Glad it worked out

I agree. It is refreshing to hear that a company gives you a warranty and then stands behind it completely.