I'm going to attempt a small path around my conservatory as a starter project - my query is on the relationship between the sub-base and the edging course's bed of concrete:
In your cross section diagram of a typical block paving setup I've noticed that the 100mm bed of concrete to lay the edging course starts halfway down the compacted sub-base - presumably 35 -50mm below the level of the finished sub-base. In the 'real world' am I expected to lay the 100mm compacted sub-base and then excavate 35 - 50mm around the edge 200mm + ? Wouldn't this excavation disturb the compacted MOT1 ? Or am I to lay a 50 - 65mm bed of sub-base, then lay the bed and edge course, wait for it to go off and then top-up the inner level to 100mm??
Is there another alternative way of achieving a sturdy edge base without messing about either excavating what I've already done, or to do two layers of thinner sub-base?
Hope you understand and can make some suggestions..
Kind regards
Ruski
Edging course bed and sub-base
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84-1093879891
It's up to you how you do it. Some contractors will lay the edge courses on a concrete bed before placing any of the sub-base - the advantage to this approach is that thge edge course blocks act as a good guide to level, even if an extra spadefiul or two of concrete is used.
Alternatively, the sub-base can be spread, levelled and compacted and then a shallow channel scooped out to accommodate the edge course bedding. This really doesn't cause much disturbance to the rest of the compacted sub-base - you'll disturb it more walking about wlooking for your clonker to hammer down the blocks, or bringing in the concrete!
However, if there was significant disturbance to the sub-base during the edge course laying, then simply run the vib plate over it all again before you place the bedding material. In most cases, simply compacting the bedding layer tightens up any loosened sub-base material.
There is a bit of a 'midway' option, where you lay a blinding of sub-base (50mm or so) beneath the areas where edge courses are to be laid, so that you save that much extra concrete. The rest of the sub-base can be laid before or after the edge courses, as you see fit, but, to be honest, I think this is more bloody trouble than it's worth!
My preferred method is to lay the edge courses at the free edges (ie, those not abutting a wall or other fixture) on an extra-depth concrete bed, get them aligned and haunched, and then place the sub-base. For the remaining edge courses, those that will not need haunching, it really doesn't matter if they are laid on a bed that's only 50mm or so in depth. In fact, some contractors lay these edge courses on plain grit sand, arguing that a concrete or cement-bound bed is not necessary as there's nowhere for the blocks to go anyway! However, I prefer a concrete or cement-bound bed because it guarantees the edge course blocks won't be dislodged when I'm screeding off for the body of the paving.
Has that cleared things up or just confused you more?
Alternatively, the sub-base can be spread, levelled and compacted and then a shallow channel scooped out to accommodate the edge course bedding. This really doesn't cause much disturbance to the rest of the compacted sub-base - you'll disturb it more walking about wlooking for your clonker to hammer down the blocks, or bringing in the concrete!
However, if there was significant disturbance to the sub-base during the edge course laying, then simply run the vib plate over it all again before you place the bedding material. In most cases, simply compacting the bedding layer tightens up any loosened sub-base material.
There is a bit of a 'midway' option, where you lay a blinding of sub-base (50mm or so) beneath the areas where edge courses are to be laid, so that you save that much extra concrete. The rest of the sub-base can be laid before or after the edge courses, as you see fit, but, to be honest, I think this is more bloody trouble than it's worth!
My preferred method is to lay the edge courses at the free edges (ie, those not abutting a wall or other fixture) on an extra-depth concrete bed, get them aligned and haunched, and then place the sub-base. For the remaining edge courses, those that will not need haunching, it really doesn't matter if they are laid on a bed that's only 50mm or so in depth. In fact, some contractors lay these edge courses on plain grit sand, arguing that a concrete or cement-bound bed is not necessary as there's nowhere for the blocks to go anyway! However, I prefer a concrete or cement-bound bed because it guarantees the edge course blocks won't be dislodged when I'm screeding off for the body of the paving.
Has that cleared things up or just confused you more?
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Ruski
- Posts: 2
- Joined: Fri Mar 12, 2004 6:43 pm
- Location: Warks
Tony
cheers for that - it's as I think I thought!! I'll go for the 'extra deep' edge bedding and then fill afterwards - seems the most practical of options.
One further q. though - I'll be using bags of ballast to create the edging bed - I think your recommendations are a 1 cement, 3 sand 6 gravel when mixing on site - does that equate to a 1:9 when using bags of ballast from the merchant?? Seems a bit weak to me - but what do I know!!!!!!
Many thanks again for your expert reply
Cheers
Ruski
cheers for that - it's as I think I thought!! I'll go for the 'extra deep' edge bedding and then fill afterwards - seems the most practical of options.
One further q. though - I'll be using bags of ballast to create the edging bed - I think your recommendations are a 1 cement, 3 sand 6 gravel when mixing on site - does that equate to a 1:9 when using bags of ballast from the merchant?? Seems a bit weak to me - but what do I know!!!!!!
Many thanks again for your expert reply
Cheers
Ruski
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84-1093879891
1:3:6 or 1:9 is the old standard 'kerb laying' mix, which is roughly equivalent to a C7.5 or C10. I know it can seem weak, but it's not actually under much strain. You could beef it up, if it would make you feel happier, but as long as it's well compacted, both as bedding and as haunching, it really will be fine, particularly as there's unlikley to be that much vehicular traffic on your conservatory path! :)