Advice needed on stained flags

[lesperks]

Hi all, i have had a contractor in and he has dropped some weber mushroom on the flags and i cant get it off! i have tried brick acid but it hasn't budged can anyone recommend a cleaner or method

Thanks Les

 

[owls]

Yes everbuild mortar stain remover. Dilute it down first, let it soak in, jet wash away.