Thread: Need help identifying these stains.

Hey guys,

I inspected a home Friday that was built 1 year ago. The house is a single story raised home. the elevation of the floor is 8 feet high with a poured concrete slab beneath the house. The owner told me that the contractor did lay the proper vapor barrier before he poured the concrete. after the owner took possession of the house some dark colored stains started to appear over the past year at different intervals. When he called the builder to investigate the cause of these stains, the builder's explanation was that the owner must have spilled something in these areas and that he should pressure wash the concrete. The owner assured me that he had not spilled anything in these areas but did do as the builder suggested and pressure washed one of the stained areas. After a few weeks the stain started to reappear. When I rubbed these stains with my fingers, it appeared to come off as a powdery substance almost like mold. Do any of you know what this is and what the cause of this staining could be?

Thanks in advance for your opinions. For your reference, I have attached some photos.

Sure looks like some type of spill, might have been during the finishing of the concrete. Leaves make it hard to see, but is there a pattern to follow as if someone was carrying a leaking bucket?

Are all the stains outside?

If they wash away, then reappear, then it could be mold or algae.

Have the owner put a drop or two of chlorine on the spots and observe/report the results.

Possibly some type of admixture in the concrete?