Laymans guide to a grano floor.... - Question regarding grano flooring

[martynx]

Having read most of the main site , i got exited about grano.. Its as rare as rocking horse manure in London but i located some & I have a plasterer coming tomorrow to apply some in my garage , he's never done grano before so i wonder if any members could give me a laymans guide ... he panicked when i said the recipe included soft sand hence this posting !

I have got myself 2 tonnes of grano, 6mm to dust & a tonne of soft sand, & 26 bags cement, these quantities were guessed from one of the caluculators on the main site, i am looking to have 50mm mimimum depth. Mixing ratio planned is 6/1/2 grano/sand/cement. Floor area is 14ftx 23ft.

Do we need to treat the existing concrete base in any way other than a wash & brush up ? (most of it was laid 3 months ago )

Do i need a DPM of any kind, polythene sheeting maybe ? ( the base is 500mm up from ground level)
can i just add some liquid waterproofer from Wickes ?

Wil 50mm be strong enough for a motorcycle workshop / occasional car ?

Is it definateley soft building sand ?

All advice greatfully recieved

By the way Jewson in Eastcote Middx got the grano in for me at 50 quid a tonne.. Prices here in NW London varied from 20-100 a tonne but only Jewson were up for sourcing it for me..

Friday UPDATE - its going down well, not really enough fat though for ultra smooth finish but more than adequate.

[Tony McC]

Probably too late now, but a grano overlay on an existing concrete base needs a bare minimum of prep. A good brushing to remove any dust, soaking with water to prevent parching the grano when it's placed, and a coat of bonding agent. If it's a new-ish concrete floor, it's usually a good idea to acid-etch it to remove any laitence - actually, acid-etching well-established concrete is no bad thing.

How did it go?