Cobbled drive jetwashed. Now: re-'grout' (I think) but with what, how?

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Hi all,

Cobbled 30+ years old drive slippery due to moss/lichen now jetwashed. Much cleaner, wow!

Quite a bit of material dislodged from between the stones per attached. My understanding is that the stones now risk becoming unstable, and best thing to do is re-'grout' them, eg by spreading sand over the stones, brushing into cracks and hosing gently.

Is this about right? What kind of sand (fine, sharp, etc)? Any tips on method (start from top/bottom - whatever)?

Drive sloping, and used to park car so subject to considerable forces.
20191202_141827_Post-jetwash_Drive.png

Any tips welcome.

Cheers,
auto

[EDIT: stones are 25x12.5cm]
 
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Kiln dried sand into the cracks - then later when the weather warms , a sand stabiliser - not a shiny block sealer . No hosing. Have a look at pavingexpert.com
 
Hi Nige F and Halitosis,
Many thanks for the prompt responses. Is there another term for "kiln-dried sand"? In Switzerland here and can't find a direct (French) translation.

Cheers,
AP
 
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No idea what it may be called over there but it is dried in an oven (kiln) to remove all moisture content. If they have block paving or driveways over there then I’d expect it to be common and available from most DIY warehouses or builders merchants. Should come in 25kg sealed bags to stay dry
 
Quartz sand used in the end; nice and dry (stocked indoors), not too fine or coarse - 0.6 to 1.5mm IIRC - and brushed in well. Diagonal brushing tip was a good one (thx Halitosis).

More time consuming and arduous than anticipated. Couple of tips/notes:
- Jetwash hired from an agricultural tool hire place, so more powerful than a domestic unit but also needing more oomph from water main. The unit stuttered unhappily when supplied via smallish-bore garden hose; only happy with fatter (19mm) supply. If hiring, ask for a fat hose and make sure you have appropriate adapters!
- ~130m2 area, with 25x12.5cm blocks (around 4000 blocks at 0.03m2 per block). Once rhythm/method established, it took ~5secs to jetwash each block, so nearly 6 hours (inc set up). 30 years of grot to remove and YMMV of course but that's probably a usable rule of thumb.
- Sand estimation tricky: I started out with worst-case as 10mm gap between blocks, to 10cm depth. Count one long and one short edge per block, so (25cm x 10cm x 1cm) + (12.5cm x 10cm x 1cm) => 375ml sand / block, or 0.375 litres x 4000 => 1500 litres. A good start but a *massive* overestimate, blocks are closer to 5cm thick, and vast majority have gaps <<5mm so required volume prob 1/10th of that. Density of the sand unknown, but a 25kg bag looked a bit smaller than a 35 litre under-sink bin liner, so maybe 20-25 litres. I bought six.
- Left drive and path to dry for a few days (beginning of last week was cold, bone dry and windy), brushing in took ~3 hours; 3 bags used.

Not really a winter job, but at least it's done and drive no longer horribly slippery in the wet!

Cheers,
auto
 

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