Sub-base laying for gravel - Is 'finings' a suitable sub-base?

[Lesley Wiseman]

Hi
We are replacing a very 'weathered' tarmac surface on a driving/parking area with gravel. We have excavated and levelled the ground, which is largely rock (sandstone). We are then spraying with sodium chlorate and then laying a semi-permeable membrane. On top of that, we are advised that a suitable material for the sub-base is the scrapings from the old yard surface, which are being termed 'finings' (and are certainly much finer than DTp1. My concern is that this material looks quite like soil, in which I fear that weeds will grow up through the gravel. I am also concerned that the fine grade of this sub-grade material will block the pores in the membrane, eventually causing rainwater to gather. Any advice gratefully received. Thank you.

[lutonlagerlout]

you get fines in MOT too lesley,water should still drain through to an extent.but your subase need to be well compacted and also remember not to put the gravel on too thick,40 mm is about right for 20 mm gravel,otherwise the tyres will sink in
cheers LLL

[Lesley Wiseman]

Thanks very much for that advice. What about the membrane - will the fine particles clog it up? I'm really concerned about the weeds issue too. Would it be better all round to use the usual DTp1 than the finings? We can use the 'finings' for hard standing in a field, where a few weeds aren't such a hassle, so it won't go to waste. What do you think?
Lesley