We've just had a new patio laid, and I can see the footprints of the builders on the slabs (photos attached). It looks kind of like they've stood in varnish before standing on the slab. Jetwashing is not removing it.
We've had them back twice to remove them - once they came when we're out, the second time it was raining so we couldn't really check their work.
I'm going to go back yet again to them - but does anyone have any ideas what it might be and how they can be removed?