Grabo suction marks on slate

[CarbonV12V]

Having some patio and path work done at the moment. Much of the patio is slate slabs and the guys have been using a couple of Grabo vacuum lifters to move them around.

They were jet washed yesterday in preparation for pointing but the the imprint of the Grabo's has come out really clear to such an extent they don't want to point until they know why and how to remove as they don't want to seal the imprint in.

They tried burning out the imprints on a spare piece of slate but other than cracking the slate the imprint is still there - see attached photo.



Any suggestions on what has caused this and whether it will go away with some water penetration/rain or whether we need to do something else such as an acid clean to remove the marks before pointing etc.

Thanks in advance.

[MARKY08]

Hi did you resolve this I've recently done some paving and this has happened to me