Patio slab screw-up

[couch67]

Hello, I just had a 16x16 slab done by a contractor, used them before and they do great work. They were done placing concrete yesterday at around 9am, but took a while to set, almost 2 hours after placing before they floated and broomed the finish. All in all they were done and gone by 12pm. Temperature was about 65F in the morning and low humidity, so a bit cool but not cold.

I watched the slab the rest of the afternoon, and when I was satisfied it had set up enough, started to mist it around 3pm. So this was almost 4 hours after they finished it. At about 5pm, I set up a sprinkler on a timer to keep a spray on the slab for 10 minutes every couple of hours.

I went to check it today, and I could see patches of spalled concrete - basically the top surface easily flaking off in areas. In the photos, the spalling appears to have happened in the lighter areas of concrete. The photos were taken after I lightly hosed the spalled pieces away (this would be 32 hours after the initial setting of concrete)

I'm thinking I hit it with water too early after the set? Could it be anything else? I'm going to contact the contractor, but I have a feeling this was self-inflicted. I think my only option is to surface grind it to get the bad surface off.

 

[couch67]

After reading up more, if the finish was done (float + broom) with too much bleed water present, it could trap water under the surface and cause the flaking.

The guys had fans on the slab to promote evaporation, and even used a leaf blower on the slab before finishing. I've never seen this done before, but I'm sure it was to speed things along and get rid of surface water. So who knows - I may have jumped to conclusions that the sprinkler to keep the slab wet was the cause.

 

[yelchevelle]

We don’t do a ton of concrete (we mostly install pavers) but I am guessing too much water at some point in their process, either mix was too wet or they added too much to the surface while finishing. There are certain things that you can’t beat using concrete for, but I hate the variables with it. That’s why I like pavers for stuff that needs to look good. 2 guarantees with concrete. 1. It’s going to get hard

2. It’s going to crack

 

[ConCretin]

WTH! That is strange looking slab. The white appearance has me baffled. Any chance they applied a tinted curing compound that is flaking off or is it actually thicker pieces of delaminated concrete? Concrete delamination is usually an 1/8" thick or so and requires a little mechanical force to dislodge. You usually don't even get delamination with a broom finish because the surface isn't sealed with steel blades.

In any case, the application of curing water is not the cause.

 

[couch67]

Thanks for the replies. Yes its not a deep de-lamination, i would say 1/16" or less that is flaking. I haven't prodded at it too much to see how much else would come off. Not sure about the different tinting in the slab, if that is due to a curing compound or something else.

Spoke to contractor this morning, he is going to work with me to make it right, regardless of fault. He said it could have been finished too early, but also mentioned I should not have hit it with water to cure as it was pretty cool out that day, and did not need additional water on day 1. He did say he's had one other de-lamination he can remember in 10 years. I've worked with them in the past and happy with their previous work, and they have a good reputation in town.

He's suggesting sandblasting to take off the top layer. Will have to see what the final finish is, but as long as it takes the top layer off I will be happy.

 

[ambenz]

Just like Carmax, you will ALWAYS pay more than you would at a dealer, if you know how to haggle.
These no haggle companies are catering to the general public that are computer savvy, but have little interactions with others.
Where as the general public raised before PC's are savvy enough to actually interact with others and know how to walk or sign a deal after haggling for a agreed value. So no surprise that your daughter is looking at a computer website to pay more for something she could get cheaper at a dealer. IMO, I would go to a dealer with her and help her to interact and haggle...it is a good exercise in dealing with others even if you cannot agree on a cost she is willing to pay.
She will learn that dealing with others is a common sense exercise and she will have for the rest of her life! ...and have a skill set you rarely see by young folks anymore.
She will save money that can be used for gas and insurance.

 

[FMB4]

Imo, floating/brushing that slab at a 65 deg amb temp should have been done no less than 3 hrs after the pour. Just over 3.5 hrs. would have been about right. Note: other factors can, of course, play into that faulty pour such as too much water in the mix, or a poorly mixed batch of concrete. I'd have your contractor remove it and pour it again, that is if you can trust him again.

 

[duneslider]

Curious what your night time temps were? When my garage was poured it lightly rained that night and was going to get cold, I called the contractor and he said he would send someone over to cover it up. They didn't show that night and we got a light freeze that came right after the light rain and one area in the garage had some areas with a really thin layer pop. Looks a lot like what your pictures look like only not as white. I was planning to grind and seal it eventually so I didn't really care, I'm not as picky as some about what my garage floor looks like though.

 

[couch67]

It was a mild evening, it did not get much less than 60

 

[couch67]

surface was sandblasted today. Very happy with the finish / texture, will be perfect for anticipated wet / freezing conditions with the hot tub. With forms peeled, everything looks great. Forgot to take photos before it got dark, will post at some point...

 

[i4ni]

If you wouldn't mind post up some pics after sand blasting for us to compare.

 

[couch67]

Here's an after pic, there is a slight difference in texture where the largest spots of delamination occurred. I'm not concerned about it, and happy with the overall finish. I do like the 'knocked down' finish of the sandblasted broomed finish. Still enough bite for wet feet, and some exposed aggregate too.

** I suppose a close up would have been useful! Doing the paver work today, will remember to take a few better shots.