Cobblers

[Roger H]

Hi All.

Does anyone have any good suggestions as to what specification I should go for when laying a edge course/drainage strip of river cobbles? These will provide a flank to a footpath of sandstone flags. The cobbles will form an edge about half a metre wide. They'll be in a public place so need to be reasonably secure although they won't take vehicle traffic. The river cobbles will be approx 100mm diameter and reflect a local detail.

I'd guess existing ones locally will be set in clay/hoggin but I think the installers of these might be looking for something more 'conventional' - for which read mortar. Would hydraulic lime be a reasonable compromise? Dry mix or wet?

The cobbled strips will abut the walls of a couple of listed buildings.

Thanks in anticipation.

 

[DaveBrigg]

Will the cobbles be walked upon? If so, whatever holds them in place will have to be pretty strong. I grouted our existing stone flags with hydraulic lime, and where shoes have been able to touch it, it has crumbled.

 

[Penners]

I'd guess existing ones locally will be set in clay/hoggin

Really? That sounds pretty un-robust. It wouldn't take many feet to dislodge them, surely?

Myself, I'd set them in concrete.

 

[Carol]

I have just had to change the surface from my chosen cobbles to granite setts on our new parking area, as the cost of foundations for the cobbles was so very expensive. We were recommended to have a concrete sub structure as cobbles need a strong base or they move and crumble. Pity, as they would have looked lovely!

Lime was not even suggested. And our builder is a trad. man!

 

[MdB]

Lime doesn't quite sound like the ideal material to me. It is useless in tension so it would need to be a very thick layer if used.

 

[biffvernon]

I'd guess existing ones locally will be set in clay/hoggin

That sounds a good idea. Mix a bit of hydrated lime in if you want. If you use OPC you will, of course, be counted as spawn of the devil, but, more immediately, will fall foul of planning now that impermeable surfaces are frowned upon. Increased flood risk and such, never mind the embodied energy and CO2 emissions. The water/drainage will be able to increase your drainage charges even if you did get planning permission.

Anyway this in PPUK so stick to hoggin. Our A-Z will get there eventually.

 

[Roger H]

These will provide a flank to a footpath of sandstone flags

Thanks all. The cobbles won't be intended to be walked upon as they are a strip half a metre wide at the edge of a flagged path. They are historically probably meant to be a drainage channel. They edge a public path and could be regarded as an 'anti pedestrian strip' to keep people off the two neighbouring buildings. There are dressed setts in the area but these are on the carriageway.

I'm suggesting a spec for my highways colleagues. I doubt hoggin will go down to well with them but hydraulic lime might. If I embed them in concrete they'd probably be unusable if they were ever taken up in the future.

 

[Moo]

Weren't cobbles used as an aid to traction for heavy horse-drawn vehicles? What did they set them in, in those pre-concrete days?

 

[biffvernon]

Hoggin.
But packed together as tightly as possible.

(Just Google "hoggin" if you're not sure.)