Block over tamac
-
paulray2452
- Posts: 4
- Joined: Thu Jan 22, 2004 9:22 am
- Location: Manchester
A freind of mine has been given quotes for a block drive but i have now found out that the drive is going to be laid over the origonal tarmac drive and that the tarmac is not going to be removed. I would lift the tarmac and make sure that the correct base was laid to ensure no faults occuring in the future. What are your thoughts and advice.
-
84-1093879891
My initial concern would be the levels. How will overlaying the bitmac tally with dpc and threshold levels?
There's no real structural problem with overlaying a bitmac base, as illustrated on the Overlaying a base page, as long as some provision is made for bedding layer drainage, but it's a rare thing to come across a bitmac drive that's suitable for such treatment.
Even using a 50mm block with the minimal 35mm bed, the Finished Paving Level (FPL) is going to be elevated by 85mm, and, as most bitmac drives are laid to 150mm below dpc, then lifting FPL by that 85mm means the gap to dpc is reduced to a worrying 65mm.
With regard to the thresholds, by the time bitmac is removed to accomodate tie-ing in, how much of the original bitmac will remain?
Personally, I'd break out and cart away the bitmac. The sub-base (assuming one is present and it's suitable) should be re-graded and then the blocks laid.
There's no real structural problem with overlaying a bitmac base, as illustrated on the Overlaying a base page, as long as some provision is made for bedding layer drainage, but it's a rare thing to come across a bitmac drive that's suitable for such treatment.
Even using a 50mm block with the minimal 35mm bed, the Finished Paving Level (FPL) is going to be elevated by 85mm, and, as most bitmac drives are laid to 150mm below dpc, then lifting FPL by that 85mm means the gap to dpc is reduced to a worrying 65mm.
With regard to the thresholds, by the time bitmac is removed to accomodate tie-ing in, how much of the original bitmac will remain?
Personally, I'd break out and cart away the bitmac. The sub-base (assuming one is present and it's suitable) should be re-graded and then the blocks laid.