Why do some spots on concrete appear to not get wet?


I was washing my car in my driveway the other day, and realized that while some spots seem to get saturated with water, other spots stay the same color and appear to stay dry the whole time. Why is this?

In: Chemistry

I work adjacent to concrete, and while I don’t know for sure, I think it might have to do with what they spray on after a pour. I know concrete after it’s poured and all smoothed out there’s generally a lot of surface treatment that goes on depending on what it’s for. Like concrete meant to be exposed usually gets polished really smooth and then it gets sprayed. Some codes require you to cure concrete for a certain amount of time after it’s poured but no one ever sits and makes sure every inch is covered equally. I usually see it in patches or spots that correspond with how I see the after treatment being sprayed.

Other than that, I think it also could do with just the general make up of concrete. Usually it’s cement, water, sand and whatever aggregate is being mixed in. If you have poorly mixed concrete or poorly finished concrete, I imagine there are areas where there is more sand and areas with more rocks etc if it’s not mixed back as it’s placed. So that area could possibly have more tiny pores absorbing water than other patches.