Marks on new paving slabs

[oron]

Hi,

An elderly relative recently hired some builders to lay some new paving in her back garden. They finished the job yesterday and several of the paving slabs have marks on them as in the below photos (the marks in the middle of the slabs)

She thought these were marks that would just wash off with the rain. However, it rained quite a lot last night and the marks were still there when I visited this morning.

Could anyone tell me what exactly these marks are, if they can be removed, or if these builders have basically just put down some poor quality paving.

Thanks for any help

 

[footprints]

paving often has white marks on it due to efflorescence it looks like the marks are the areas that have not suffered if it is efflorescence it will weather off in time mine took almost a year.

 

[footprints]

https://www.marshalls.co.uk/gardens-and-driveways/blog/what-is-efflorescence-and-how-to-treat-it

 

[oron]

Thanks for the replies. Maybe I'm wrong, but isn't efflorescence light coloured stains and not dark ones as in my photos?

 

[footprints]

I think the bits that are dark are the bits without efflorescence.

 

[Charlie George]

They look like marks from rubber maul to level slabs,should wear off eventually.

 

[domdee]

They look like marks from rubber maul to level slabs,should wear off eventually.

that was my thoughts