Preparation Concrete grinding prior to tiling - Tile Advice

[JS1]

I've just had a 7m x 4m concrete slab laid by a contractor to fix 20mm porcelain to as a patio. Despite the written and verbal specification/briefing stating the importance of the slab being flat (+/-2mm over 2mm) the end result is a slab with high spots of 14mm in several areas. The only way to solve the problem is to grind the slab flat. Can anyone advise on the considerations to achieving this - the slab contractor states he can hire a machine but I'm nervous about allowing him to do this, is it a specialist job or within the capabilities of a competent DIY'er. Any advice gratefully received. Thanks

 

[Taylormade]

No it’s not a specialist job. Do you believe he can rectify the errors if not?

 

[JS1]

No it’s not a specialist job. Do you believe he can rectify the errors if not?

I hope he can, if it's not a specialist job it should be capable of being done by a reasonably practical person. I haven't spoken with him to establish any prior experience with grinding work perhaps that's the next step?