Sub base - Reusing existing sub base

[Ian Rutherford 1]

Hi !

I have just started to block pave my drive - 100 m2. I have ripped up the old tarmac (the house is 20 years old and the drive is the original) and found what looks like reasonable hardcore underneath. I am doing checks to see if it is the right thickness and if it is then I was proposing to reuse it rather than buy a load of new hardcore. Is this acceptable ?

Also, I first block paved a drive 6 years ago and although I was pleased with the result trams lines appeared after about 6 months. Nothing too serious but irritating nevertheless. I thought I had 'wacked' it properly. How can I avoid this issue ?

Any advice welcome !! Thanks !!

[Tony McC]

Yes, you can re-use the existing sub-base, as long as it is 'competent', which means it is "up to the job". It may need regulating (re-levelling) and re-compacting if iut's been disturbed during the excavbation works, but, if it consists of a decent type of material and is at least 100mm thick, then it should be fine.

To avoid channelisation (your tramlines), you really need to ensure the sub-base is up to scratch. Channelisation occurs when the same 'track' is used day in and day out, repeatedly loading the same 'channels' of paving. An adequate sub-base should prevent this happening - the single biggest cause of channelisation on residential driveways is the sub-base, or lack thereof. If you have any real concerns, then consider using a thicker sub-base; say 150mm rather than 100mm, and, if the sub-grade is iffy in any way, use a geo-textile to help support the sub-base.