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My new driveway was poured on a humid day after much rain. As it dried, big streaks of green-black "mold" became obvious. There are fist sized balls of it also. These are not on the surface but trapped at varying levels in the concrete. The builder says this will disappear in a month. Is that true? Will pockets be left in the concrete that will weaken it? Will it be discolored? I live in MI. Thanks for ANY advice.

I don't know of anything that will do what you describe. Maybe you can find someone else to look at the concrete to tell you what happened. fresh concrete is so alkaline that for a little while it s a really hostile environment for any living thing. Then mold and mildew takes a bit of time before it puts out the black part which is the reproductive stage. Any voids or spaces inside the slab are permanent. Whatever the substance that was in those holes it wasn't supposed to be there. I would certainly question the durability of the concrete. It appears to have been contaminated with something. You need an eyeball inspection by someone who can tell you what is going on. You may need to locate a residential general contrctor who can do the inspection for you. Offer to pay for a written opinion. Then see what happens.

I would contact the company that supplyed the concrete and have them send a rep out to look at it. I've never heard or seen anything like you discribed.

Jdn and joecaption--thanks for the help. I think a local cement contractor is the best bet now for an opinion. The company who poured it has sent out a rep who said "this happens every 250 driveways or so" He refused to talk about what it was or driveway durability. He just said it "might" go away in a month.

i'm w/jd & joey,,, in 35 yrs, never saw that condition,,, curious how you know its at varying levels, tho,,, i STILL can't see thru conc past the surface & its not because i need glass's.

call the conc supplier & start yelling !!! either your contractor's peeing on your leg & telling you its raining OR he's invented a reason for a problem he's hiding,,, bet a pro eng'll only charge $300 for an opinion letter - good money for those initials when you talk to the readi-mix plant.

i GOTTA hear this 1

One time I remember a load of washed rock where clay balls had made it all the way through the screening and washing process. If that rock had been used for concrete aggregate there would have been soft lumps inside the concrete.