Is this normal for concrete?

[ju2tin]

Finally had the concrete slab floor poured in my pole barn garage about a week ago. It's supposed to have a smooth finish. It started out all the same color, but as it's been curing, these splotchy light-colored areas have been coming out and spreading around:

Here's a close-up:

And another:

The light-colored areas are pretty much as smooth as the dark areas; they just look lighter. Never had a slab poured before, so is this normal and/or acceptable for concrete? Or is it a sign of problems down the road? And will the floor always have this mottled light-and-dark appearance, or will it all turn the same color over time?

Thanks.

 

[STx]

Mine cured unevenly at first and ended all.the same color. I think it's just the moisture wicking out differently in some areas. I dampened mine acouple of times a day for the first week or so, it kept the appearance a little more even.

 

[John Fitzgerald]

It's soluble salts leaching out of the concrete, called efflorescence. On outdoor slabs, this will get washed off by rain or wetting. You should clean it off with water, and ventilate the building well until cured. It can cause a little bit of roughness in the surface if allowed to remain. It's common in indoor slabs, and even outdoor ones where excess humidity is present.

 

[Tractor Seabee]

Did your contractor put calcium in the mix for cold weather freeze protection? It will leach out like that. If so, that is a huge mistake as calcium corrodes any embedded metals, like reinforcing or anchor bolts. There are better ways to do cold weather concrete. Good to see you got those control joints done. Hope it was as soon as they could get the saw on it. Next day is too late.

Ron

 

[John Fitzgerald]

Did your contractor put calcium in the mix for cold weather freeze protection? It will leach out like that. If so, that is a huge mistake as calcium corrodes any embedded metals, like reinforcing or anchor bolts. There are better ways to do cold weather concrete. Good to see you got those control joints done. Hope it was as soon as they could get the saw on it. Next day is too late.

Ron

They would not use calcium chloride this time of year, especially in an indoor slab. Yes, there are better ways than CC. Concrete will have efflorescence without any calcium chloride under humid conditions on an indoor slab. If they put too much water on it to work it, that will cause that kind of bloom to be worse. Best solution is to clean it off with a vinegar solution, wipe that up, then use a baking soda neutralizing solution afterward, followed by rinse.

 

[ju2tin]

Did your contractor put calcium in the mix for cold weather freeze protection? It will leach out like that. If so, that is a huge mistake as calcium corrodes any embedded metals, like reinforcing or anchor bolts. There are better ways to do cold weather concrete. Good to see you got those control joints done. Hope it was as soon as they could get the saw on it. Next day is too late.

Ron

They used Daraset Non-Chloride, which I have read is supposed to not damage rebar in the concrete.

I'm a little concerned about the control joints because they didn't cut them the same day. However, they did cut them about 19 hours after finishing the final pour and about 13 hours after finishing the power troweling. Acccording to the load tickets, they started pouring around 9:30am, and finished pouring by 11:35am. They were still power-troweling the surface when I came home around 5:45pm or so. Then they came back early the next morning (I think around 7:30am or so) to cut the joints.

Their reason for not cutting the joints was something about the weather; I think they said it was too cold and rainy out, so the concrete was taking longer to firm up? (It was a bit rainy, and some rain was coming in through the open garage doors, which wouldn't close because they needed to be readjusted for the thickness of the concrete slab.) This may have been BS and they just ran out of time before their workers went home. Probably it was taking longer to cure, but also they couldn't keep their workers on the job site all night long waiting to cut.

I would have liked them to cut the joints sooner, but so far so good.

 

[ju2tin]

They would not use calcium chloride this time of year, especially in an indoor slab. Yes, there are better ways than CC. Concrete will have efflorescence without any calcium chloride under humid conditions on an indoor slab. If they put too much water on it to work it, that will cause that kind of bloom to be worse. Best solution is to clean it off with a vinegar solution, wipe that up, then use a baking soda neutralizing solution afterward, followed by rinse.

Yeesh. I don't put that much work into maintaining the wood floors in my house! :laughing:

Now, where did I put that mop and bucket...

 

[ju2tin]

Mine cured unevenly at first and ended all.the same color. I think it's just the moisture wicking out differently in some areas. I dampened mine acouple of times a day for the first week or so, it kept the appearance a little more even.

Thanks. I don't really mind the look, although it would be nice if the color evens out a bit. Mainly I was concerned if it meant the concrete was weakened. Glad to hear that's not it.

 

[John Fitzgerald]

I haven't seen any control joints in a residential garage around here, and I have seen lots of them. Most are at least 22 feet square, some as big as 36 feet by 24 feet. They crack eventually, but not bad enough to affect use. I think your joints will be fine, and your slab probably won't crack much, if any.

 

[ju2tin]

I haven't seen any control joints in a residential garage around here, and I have seen lots of them. Most are at least 22 feet square, some as big as 36 feet by 24 feet. They crack eventually, but not bad enough to affect use. I think your joints will be fine, and your slab probably won't crack much, if any.

Thanks. Mine are 8' square! So I hope that will give any future cracks plenty of nice cuts to form in.