The Brew Cabin

I have laid down some slabs on a dry (10:1 sharp sand
/ cement) mix, is this right?

the gap between each slab is 5mm

Can I use the sharp sand for dry jointing it.

please advise as appropriate . thank you

10:1 for the bedding is fine. However, for the jointing, a genuine jointing sand is preferred to plain old grit/sharp/coarse sand. It's a minor point, and there's nowt to stop you using sharp sand if you want, but a proper jointing sand is specifically selected to interlock as it settles into place and so provide a tighter, well-filled joint.