Concrete stain removal help
Hello - I am trying to figure out how best to remove my parents outdoor, covered concrete patio stains. These have been there since they did some remodeling work 15 yrs or so ago. The contractor used this patio to store all building materials including indoor concrete stain and they never had it cleaned. From the looks of it, I am not sure if these are organic stains in nature or require a harsher acid or etching treatment. The worst part of the patio is closer to the edge so rain may reach this and wonder if these might be something else. My parents live far away from me, but plan to clean this when I visit next month for a weekend DIY project. Hose or pressure washing does little to these dark stains apparently. Any help is appreciated on how best to prepare and handle this project. Thanks in advance.