Black specks in garage concrete flooring...

[pmdiyer]

I am currently in the process of zhuzhing up my garage, we had vinyl rolls covering the concrete floor before. I removed it the other day to be met with little lumps of black charcoal/tarmac looking specks in the concrete. It wasn’t stuck down with adhesive so it's not residue from adhesive.

I’ve tried scrubbing the floor several times and used the jet washer on it aswell. Some of the specks have been washed away whilst other bits are embedded in the concrete. Once water touches the specks, it begins to bleed brown similar to coffee granules. Someone said it might be mould but some of the specks are embedded within the concrete. Could this happen?

So, my question is... What is it and is this normal?

 

[freddiemercurystwin]

I can't help with your post but great use of the English language there "zhuzhing up", haven't heard that expression in years, I shall attempt to use that more often.

 

[dazlight]

It’s lignite