Is it ok To lay block paviors on old tarmac??
- Thread starter aspley
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Okay aspley. Straight answer. Hope you understand it.
Yes it is now possible to lay block paving over either concrete or bitmac, providing good falls of at least 1 in 60 are already in place, either to a side to side camber or across the width.
However the block paving can not be laid in the traditional method. There must be a fin drain laid either side if the fall is a camber or one side only if cross fall. The fin drain, or drains must connect to a suitably designed soak away. There must be a geo-composite drainage core between the impervious bitmac and the sand bedding course. This core will consist of a permeable membrane, the drainage core and a bottom impermeable membrane. This composite must be taken down the fin drain trench to the bottom of the fin drain perforated pipe.
This system does work, but the disadvantages are.
1. If existing drive abuts house wall, lifting up new block driveway by approx 110mm may interfere with DPC
2. If existing drive marries in to existing back edge of footpath, then you have a lot of cobbling round to do at that point.
3. Additional Cost.
4. All of this drainage will be 90% redundant after two or three years when the paving has matured to being 90% impermeable.
There are cheaper ways of laying blocks over a impermeable sub base, that we have tried, but they did cause us a lot of problems in the initial maturing period, and if we did use these methods again, they would need a lot of improvement.
With regard to bitmac planning’s. Yes they have been used for years as hardcore, but would suggest you only, use them underneath concrete, new bitmac or old field tracks, and not underneath block paving as over time planning’s revert back to an impervious base.
We would not advise anyone to lay block paving over an impervious surface, unless they fully understand how to deal with the hydrostatic pressure from water in the sand bedding layer.
Your choice, Help this helps.
oldun
Yes it is now possible to lay block paving over either concrete or bitmac, providing good falls of at least 1 in 60 are already in place, either to a side to side camber or across the width.
However the block paving can not be laid in the traditional method. There must be a fin drain laid either side if the fall is a camber or one side only if cross fall. The fin drain, or drains must connect to a suitably designed soak away. There must be a geo-composite drainage core between the impervious bitmac and the sand bedding course. This core will consist of a permeable membrane, the drainage core and a bottom impermeable membrane. This composite must be taken down the fin drain trench to the bottom of the fin drain perforated pipe.
This system does work, but the disadvantages are.
1. If existing drive abuts house wall, lifting up new block driveway by approx 110mm may interfere with DPC
2. If existing drive marries in to existing back edge of footpath, then you have a lot of cobbling round to do at that point.
3. Additional Cost.
4. All of this drainage will be 90% redundant after two or three years when the paving has matured to being 90% impermeable.
There are cheaper ways of laying blocks over a impermeable sub base, that we have tried, but they did cause us a lot of problems in the initial maturing period, and if we did use these methods again, they would need a lot of improvement.
With regard to bitmac planning’s. Yes they have been used for years as hardcore, but would suggest you only, use them underneath concrete, new bitmac or old field tracks, and not underneath block paving as over time planning’s revert back to an impervious base.
We would not advise anyone to lay block paving over an impervious surface, unless they fully understand how to deal with the hydrostatic pressure from water in the sand bedding layer.
Your choice, Help this helps.
oldun
Thanks for that Theoldun...........it all makes sense and leads me to conclude that it's worth giving it a go as the job is for myself so .........'time + cost saved=risk worth taking'
Now that is what forums are about
Now that is what forums are about
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I have also seen it done on a new housing development. Tar laid on roads until all houses complete then roads finished with block paving. Tar was punctured in a grid pattern 1m apart for drainage and road was adopted by roads authority no problem
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Well, it's a good job i looked past this helpful comment !whats your horse called?
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I was wondering of you managed to lay pavers on top of tarmac without any issues. I'm considering doing this myself any pointers on doing this?
Does this also apply to concrete? Reason I ask is that 15 years go I prepared my own drive before paving (seen too many sink where cars sit on them). I probably went over the top but after clearing the soil, I put down probably 6" of what my mate called 'type 1', compacted it with a whacker plate, then, and only because I got it for free and saw it being done to a building near where I worked, I helped myself to a load of leftover twisted steel and some plastic cups that they sat on and built a reinforced grid before covering the whole area with about 4" of concrete. I then got a block paving specialist in to supply and lay the blocks. Never had any problem with it, it never sank and is as level as the day it was laid despite having some very heavy vehicles sitting on it.
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as stated above most newbuild roads are are constructed with base coat tarmac then 70mm holes punch through filled with coarse grit then sanded and paved so as long as your levels are okay it doable not the right way as its done for temp road surface
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Thank you for your response. My drive is quite steep and you say 'as long as your levels are okay' does this mean it can only be done on level ground or is a gradient okay?
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the main thing I'd say is don't build up over your damp proof course of your house. It's an extremely popular thing to do but it's a good cause of penetrating damp. Ideally keep over 1 brick course below, but 2 is the gold standard where rain will be splashing off the ground.
My other comment is make sure you bed them on sand, someone on our road laid them directly on concrete, they haven't sunk at all, but loads of them have cracked as the base is too hard.
My other comment is make sure you bed them on sand, someone on our road laid them directly on concrete, they haven't sunk at all, but loads of them have cracked as the base is too hard.
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