The Brew Cabin

I have narrowed down a decorative aggregate to cover my drive (which i dug out a little deep ended up filling with 7 tonnes of DtP and its not that big, but hey i bet i wont get drainage problems :) )
The aggregates i have been looking at come in 4 sizes from 6 mm to 20 mm we were going for the 20mm maybe 14mm, at 20 and 14mm how much would a 1 tonne bag cover in Sq Metres at approx 40 mm deep or should i go deeper... Thanks in advance

i would go for less than 14mm if poss, average is 1.2 tns per cubic mtr ie; 0.048tn / sq mtr @ 40mm depth or half a tonne will cover 10 mtr2 or more as i woulld cover at about 30-35mm depth.

That figure for gravel density is somewhat light. The usual figure for gravel is 1.7 tonnes per cubic metre, although there is some variation depending on size (smaller gravel is 'denser') and, of course, rock type (granite chipping are denser than gritstone chippings).

Overall, a typical 10-14mm gravel has a coverage rate of 15-20m² per tonne at 30-35mm depth.

I was under the impression that 1.8tns per mtr was used for calculating heavy material such as soil or clay we ussually estimate a usage of 1 tn per 16m2 at 1 inch depth and are usually quite accurate i agree with Tony that gravel density varies (due to there being more voids in larger gravels per mtr 3) but im not sure it varies that much if i were you i would order somewhere inbetween and see how you go because if you end up with a few spair tns you will end up deeper than you want to be and this will cause you a never ending maintenance problem.

What would the "never ending maintenance problem" be if the gravel was too deep, say to a depth of 50 - 75mm.

30 - 35mm seems very thin (I would have imagined) for gravel depth on a drive to take vehicular traffic, or has experience over the years brought you to this ideal depth?

gravel is not stable like mot or similar sub bases and if it is too deep then it will furrow when trafficed resulting in you constantly raking it level. 50mm is probably ok but i really would not go any deeper. Alan D.