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

[CarbonV12V]

MARKY08 said:

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

Hi sorry for the delay. No this was not resolved and the contractor is in the process of having to replace all the slabs that were affected - about 50 in total.

The marks are still visible when the slabs get damp and as they are drying out - it was not a surface mark but presumed to be where the primer has either been pulled through into the slate slab or the slab has been crushed by the power of the Grabbo vacuum.

It would suggest that the Grabbo is not suitable for porous stone/slate but they will not admit that. The contractor followed the recommended installation process.

What issues are you having and what material - feel free to message me?