The Brew Cabin

This is a great site and very informative. I am having a block paved driveway done at this very monent and the contractor has used some of the old tarmac beneath the sub-base. He dug out the depth well beyond 200mm, removing a lot of heavy clay in the process. He has used some of the old tarmac drive beneath the sub-base which is at least 100mm of type 1. Does this sound reasonable ? In a few places there is are some chunks of tarmac mixed in with the Type 1, but generally it seems to be pretty consistent across the whole area.

Has he done the right thing removing clay and replacing it with old tarmac, or is he just avoiding having too much tarmac to dispose of? He took away most of the old tarmac away anyway so I cant think of any sinister reasons for what he has done. Advice welcomed, he's coming back tomorrow to do the edging...


(Edited by rspecial at 3:13 pm on Oct. 1, 2002)

It's a little bit naughty to use old bitmac as a fill layer, as it does degrade over time, but, for a residential driveway, it should be ok, as long as it hasn't been used to skimp on the actual sub-base, and doesn't protrude into the bedding layer.

It should have been broken up into 'chunks' no bigger than 50mm and evenly spread over the exposed sub-grade as what we call a 'capping layer'. I suppose the contractor has elected to use it to replace some soft clay or other suspect sub-grade material, which is better than leaving the iffy stuff in place, but not as good as building-up with genuine sub-base material or using a geo-membrane.

Depending on how the excavated material is being disposed, it can be cheaper to send inert clay to the landfill, than to send old bitmac, as that is NOT inert and has to be treated as degradable waste, attracting a higher level of landfill tax. Some companies charge a standard rate for all waste; others charge less for inert. So, maybe your contractor is being a little bit clever (they'll probably call it "environmentally friendly" ) by sending the clay to the tip, rather than bitmac. :)

As long as you're getting an insurance-backed written guarantee, there's probably nowt to worry about.

Thanks for the prompt reply - its really useful and I spoke to the contractor after reading it. He did use the tarmac to make up a small area of poor subsoil where the original house builders had dumped a load of broken up clay/rubbish etc. He assures me he put a good layer of type 1 on top and certainly used a big wacker to compress it all so all should be fine :).

(Edited by rspecial at 5:53 pm on Oct. 1, 2002)


(Edited by rspecial at 5:53 pm on Oct. 1, 2002)