Tarmac sub-base - What to use

[YorkshireDoug]

I've had a bit of a nightmare with getting my driveway done and would like some advice to get it finished.

I dug out my driveway to 225mm ready for sub-base and tarmac. I had a builder in to put sett stones in as a nice edging for the tarmac and he filled the area with roughly 150mm of 40mm to dust crusher run. Once he had finished, the tarmac subcontractor complained that the sub-base was low in a few areas and asked for it to be rectified. The builder came back and levelled it. The following day the tarmac guy came back and filled it further with what I can only assume was waste product (crushed brick, tarmac, stone, clay etc.). I wasn't impressed as this left as little as 40mm for tarmac in some areas (185mm sub-base) and wasn't quality material IMO. He is no longer doing the tarmac.

I have dug out the material that the tarmac guy put down, along with some of the crusher run that now contained clay. I am now at about 100mm to 125mm thick, 40mm crusher run sub-base thickness. So I need to bring it back up by around 25mm to 50mm to get to my desired level.

Can I use 20mm crusher run to do this last inch or two or does it have to be 40mm crush? My nearest merchants only have 20mm crusher run. My builder has advised me that 20mm will make it easier for me to reach my desired level, which makes sense. But on this website it advises 40mm crusher run for a sub-base and I cant find any conclusive information that says 20mm isn't suitable.

I'm probably making a mountain out of a mole hill, but I just want it to be right after I've ploughed so much time, effort and money into it.

Thanks

[Tony McC]

You should be OK with 20mm crusher run - it would certainly be better than the crap put in by the blacktop guy, which sounds suspiciously like the lucky dip that is SF2 (which I think is now referred to as SF6, like Windscale was renamed Sellafield in an attempt to assuage it's appalling reputation!)

Roughen/loosen the top of the existing sub-base, even if it's just with a rake, add the new aggregate, and then re-compact the lot. By loosening the top, you help the added material embed itself and minimise the risk of any lateral slippage/creep.

[YorkshireDoug]

Thanks for the input Tony. Appreciated.

I'll be sure to give it a good once over with the rake then.