The basement floor slab in this new home is a problem!
What's going on with this floor? It is only four months old.
The homeowners have been in the house for one month.
The basement is the indoor play zone for three small children. There is a lot going on down there!
A week or so prior to this photo spots developed in one area of the floor.
During the next few days these spots grew in size. The homeowners punctured one spot with a chop stick (!) and it opened right up.
The hole is about 1" deep and the goop inside smells like oil.
Of course they called me to ask if I knew what was going on. My answer? No.
So I went to the house to have a look, took some photos, went on the web, and asked some experts. The bottom line is that nobody really knows, but the consensus of opinion is what I speculated on site.
The aggregate put onto the floor had a bit of oil in it, which globbed up, rested near the surface cream, and festered near the surface, finally producing stains. The stains grew, and the area or cream immediately over each glob was very thin.
You can see from the photo that the largest stain was not very big at the time of the photo.
And by the time I saw it the goop had hardened, but could still get onto my finger, and it smelled like oil.
The builder was going to visit the house to see what was up. I'm waiting to hear the report.
The experts on line also said what I thought at the time I saw this: that area of flooring would need to be cut out and re-poured. The slab is about 5" thick.
Still, more time needs to pass to see if there are any more areas which develop the stains. They don't want to do anything until the entire scope of what is needed can be known.
My recommendation: sometimes things don't happen at first in new construction! But when they do it is best to consult a professional expert. We don't know what we don't know. And sometimes the experts don't know! But still, get the best advice and go ahead.