Weeds on monoblock

[Uncle Peter]

Why is it that roads made of monoblock never get weeds, but driveways do? Is something different about them? If so why don't they do that with driveways?

[cd]

I'd have thought provided you underlay with a decent grade of black plastic and mix plenty of salt in with the sharp sand base, you won't get anything coming up through.

[GB]

Don't roads also have about 6 feet of foundations?

[Nightjar]

Kent CC specifies a minimum of 450mm, with up to 600mm for heavy commercial traffic on a weak subsoil.

[GB]

Is that all? Roman roads were 1 to 1.5m in depth, and whilst they did not have the benefit of modern construction/materials, they did not have to stand up to 50 tonne lorries, either.

Anyway, even 450mm would tend to keep the weeds down.

[Uncle Peter]

Surely the weeds grow in the tiny amount of topsoil generated from passing feet etc.

[Uncle Peter]

I was thinking where I have gravel in my garden, with lots of weeds (plastic underlay doesn't work!), to take up the gravel, place a solid concrete base, then replace the gravel on top.

[harryagain]

Only the traffic keeps weeds down. You find plenty of weeds growing in the centre of narrow country lanes where wheels don't pass down the centre of the road.

Also salt applied in Winter kills off weeds

[Chris Hogg]

+1 It's the traffic that keeps the weeds down. Our block drive gets weeds and moss, but not on the two parallel strips that the car passes over. We live down a mile-long narrow tarmac'd country lane, and the centre of that lane is green with moss and weeds.

[Chris J Dixon]

As far as I can tell, most weeds on block driveways are not growing through from beneath, but establish themselves in the mix of sand and deposited dirt in the gaps.

Roadways generally get enough traffic to wipe out anything before it has chance to grow.

Chris

[Brian Gaff]

And of course more traffic on roads and probably they get killed off by the salting or even get sprayed for weeds. Brian

[Nightjar]

If I understand the document I found correctly, on strong sub-soils it could be less for strength, but 450mm is the minimum to stop frost heave in the soil under the road.

Especially as it includes a thick layer of concrete under the top surface.

[Martin Brown]

Although not the case on some quieter rural single track lanes where there can be grass growing down the middle. Roads are also periodically hit with glyphosate to take down the weeds at the kerb margins.

[charles]

known as "3 ply roads"

[Chris J Dixon]

Those are the times when caravanning that I really hope I'm on the right route.

Chris

[Huge]

My wife has a unerring ability to find B&Bs which are down narrow, steep, winding lanes with big banks either side when I'm towing my race car, so I sympathise.

[Uncle Peter]

I'm thinking of rural areas with little traffic. Just a culdesac etc. The cars won't drive on every part of it, yet there are no weeds at all.

[Uncle Peter]

No, the gravel is there because I want it there. The concrete is to stop the weeds.

[Uncle Peter]

But surely the weeds root in the dirt dropped into that 4" of chippings?

[Uncle Peter]

But that's a privately done road presumably? I've never seen a single weed (just a slight bit of moss) on a commercially done one (which services 20 houses or more).