B
Bill
Personally, for that type of limestone and the joint width, I would use silver sand and cement. (save a lot of money too)
If you are not comfortable with that idea then you need to find a specific wide joint grout variety - there are plenty on the market.
Do try and work as clean as you can and you should be able to seal those after laying but before grouting. Always do a test in an inconspicuous area.
A 10mm trowel is not enough and I suggest getting a 20mm round notch like this one
20mm x 15mm U Notched Extra Deep & Extra Long Trowel £11.69 + VAT in stock - next day UK delivery plus Tile Cutters and Tiling Tools - https://www.tradetiler.com/20mm-x-15mm-u-notched-extra-deep-extra-long-trowel.html
Back butter the slabs too.
If you are not comfortable with that idea then you need to find a specific wide joint grout variety - there are plenty on the market.
Do try and work as clean as you can and you should be able to seal those after laying but before grouting. Always do a test in an inconspicuous area.
A 10mm trowel is not enough and I suggest getting a 20mm round notch like this one
20mm x 15mm U Notched Extra Deep & Extra Long Trowel £11.69 + VAT in stock - next day UK delivery plus Tile Cutters and Tiling Tools - https://www.tradetiler.com/20mm-x-15mm-u-notched-extra-deep-extra-long-trowel.html
Back butter the slabs too.