Cobbles / granite setts

jkgray

I am currently considering putting in a cobble / granite set driveway.

I have been offered some surplus granite sets from a larger job (I have been given spec but have not seen them yet) on the following basis - Around 1800 block - each 8 inches (~20 cm) long x 4 inches (~10 cm) wide x 3 inches (~7.5 cm) high. I was told they would weigh about 3.5 tones.

On the basis of the dimensions I thought these would cover about 36 m2 [each block covers 0.02 m2, on basis of 0.2m x 0.1m meaning would need 50 per m2 and there are 1800 block]. Leaving aside that I have made no allowance for the grout (so in fact coverage woudl be greater), is my math correct?

The other issue is the weight - if 1800 cobbles weigh about 3.5 ton, this would mean each cobble weights about 1.75 kg (based on 1 short ton = 907 kg; 3.5 t x 907 = 3174.5 kg; divided by 1800 = 1.75 kg) which seemed awfully light.

When I raised this I was told there was mistake and the block weight was more like 3.8 kg, so the estimated total weight was around around 6.8 tons.

I have seen different measurements expressed elsewhere for 100mm x 100mm x 50 mm cobbles (so less than half the size of these ones) but these have ranged from 9kg per cobble to 'you get about 2-2.5 m2 per tonne'.

On the basis of 2.5m2 per ton about 6.8 ton would only cover 17 m2. Am I going wrong somewhere?

Is it likely these block are manufactured block (which I've heard is lighter) rather than real granite?

Any thoughts appreciated.

Thanks:beer:

jkgray

anyone? anyone? :rolleyes:

Canucklehead

Good afternoon: an excellent paving website and forum here.

HTH

Canucklehead