The Brew Cabin

I'm looking to extend my driveway to accomodate 2 cars, and I want to block pave with Armstrong cobbles,no problem there I hope?

I have had qoutations from 3 companies quoting for a concrete sub base, and cobbles set on a Sand/cement screed. However another co is suggesting I would be best to go for the Geo -textile base Geo -Grid for reinforcement, then Grano -lithic Screed.

I am somewhat confused and noting the latter is some £400 more expensive,I need convincing this is the best option. Can anyone help ?

Many Thanks

Hi Mark,

the cobbles you refer to are the rounded beach cobbles, aren't they?

These are often laid in a sand/cement matrix, as illustarted on the Duckstones page, but the grano is a better medium, as it's much harder wearing. However, it needs to be carefully batched when mixing to keep it all the same colour when cured.

Just what the geo-membrane is for, I'm not sure, unless you're on rteally, really crap ground. The spec I would probably opt for is 100-150mm of C20 concrete with 25-75mm of grano screed bonded to the top and the cobbles set into that.

Has the contractor offered an explanation of why the geo-membrane is necessary?

Tony, thanks for the info.

just to confirm the "cobbles" are Armstrong "Beamish Cobbles", more of a "round edge" 60mm block,rather than as discribed in the duckstones section.

The ground is fine, and as suggested everyone else I have spoken to suggests a 150mm concrete base would be ok, it was just this one contractor who suggested that the concrete would crack and that we would get drainage problems.

He suggested this Geo Grid as a way to bond / hold the compacted hardcore together as the best option for longevity and drainage, as for the Geo textile, I'm not convinced myself.

I,m thinking of just going ahead with the Concrete sub base with the Beamish cobbles /blocks set on sand/cement screed 50mm, as has been qouted, saving me £400, is this the best option Tony ?

Many Thanks
Mark

Hi again,

so, they're a block, are they? Just goes to show what a nightmare paving terminology can be! I must update my library with Armstrongs products.

I'm not familiar with this exact product, so let me check it out before making further comment on the ebst laying method. However, the comments made about geo-membranes doesn't hold water, to coin a phrase.

Geo-grid *can* be used to stabilise sub-grades and sub-bases, but it tends to be used on large projects that will be subjected to exceptional stresses, or over 'made-up' ground. If a proper sub-base material is used rather than the rather unspecific "hardcore", there should be no need for a geogrid beneath a residential driveway.

And just how it is supposed to help drainage, I've absolutely no idea. A concrete or other cementitious bedding medium will be more or less impermeable, so what use is a geo-membrane at the interface of the bedding and the sub-base? I wonder if he means a drrainage composite?

Anyway, I'll take myself off to Armstrongs website to learn more about what passes for cobbles up there in the north-east. :~)

:)
Thanks for the info. Appreciate your time and effort. Sounds like the geogrid/ membrane are superfluous to our requirements and obviously more expensive.

Best of luck with Armstrong's website.
Mark.

It's not very good, is it? You'd think they'd at least have pictures of their products!! Still, that's what happens when you pay nerds with no understanding of the building trade to build your website. :(

I spoke to them on the 'phone and they promise info in the post tomorrow. Mmm. We'll see. ;)

The info, sparse as it is, arrived from Armstrong in this morning's post. The Beamish Cobbles are their attempt at a natural sett-like paving block, similar to the Rialta range from Marshalls or the Ionica from RMC. They are laid in the same way as those two better known ranges, ie, as part of a flexible system, just as described on the block paving page.
Quite why you're being told to use a concrete sub-base, I'm not sure, unless there are problems with bad ground, but the spec I would suggest is for 100-150mm of DTp1, with a 35-50mm bedding course of grit sand and then the Beamish Cobbles, laid hand-tight in courses.

If you have any specific queries about the blocks themseklves, the guy to speak to is Mark at Armstrong's Paving Block division in Consett. Tel is 01207 505655 or sales@thomasarmstrong.co.uk If you have any other questions about the construction method, you're welcome to post back here.
If you go ahead with the work, I'd like to see pictures of the Beamish Cobbles when they're laid. :)