The Brew Cabin

Posted: **Mon Nov 23, 2020 10:23 am**

Hi,

First-time poster and longtime admirer of this website. I moved over from Ireland in 2012, I came straight out of university to work as a setting out Engineer in Manchester, and to be honest, I was a bit wet behind the ears. This website was a godsend giving me clear and to the point descriptions of everything from drainage installation to paving/flag laying.

Last week I started helping out on a small housing project that is running behind and has had some level issues. In one garden the flagger is laying porcelain flags onto a wet mix mortar directly onto approx 4-inch of pipe bedding. Has anyone seen pipe bedding used as a sub-base layer? I've checked the website and forum but couldn't see anything. When I questioned it I was told that it's the way the Germans do it! The drawings stated a more typical construction of sand on asphalt binder on type 1.

Cheers,

Mick

Posted: **Mon Nov 23, 2020 11:08 am**

Mick, I thought we'd stopped exporting all our good people when we came over in the 60s! Naaah....I know it still happens, but not as common as it was when I was younger. More opportunities at home, nowadays.

Anyway: porcelain on mortar on pipe-bedding....a tale of half-truths and misunderstanding.

For all sorts of silly (genuinely silly!) reasons, we accept porcelain laid on a wet mortar in Britain and Ireland, even though it's not really the best laying method. What the hell! It's cheap and it's quick! All there is to say is that, as long as there's a suitable bond bridge primer and a decent sub-base, it's not really the end of the world.

But pipe-bedding (A10) as sub-base? I know it regularly gets used as such on new-build housing estates because the groundworker, responsible for the drainage installation, the foundations and the surround paving, bought in a few 20-tonne loads and has plenty left over by the time it comes to the paving. Why waste it? Use it as an 'alternative' to a genuine Type 1 - who's to know?

The claim that it's a German methodology is not quite correct. The modern German method, and one we *will* be adopting over the coming decade (if the relevant BS cttee can get their act together) uses a no-fines sub-base, similar to a Type 3 (but often a bit smaller, say 20-5) and then a 'Trass' bedding, which is a no-fines mortar based on grit, resulting in a bedding material with the texture of childrens' rice-crispie cakes. The idea is to have a highly permeable sub-structure to take water away from the surface and from the immediate vicinity of the flags.

So, the Germans (and many of the Scandiwegians, Austrians, Poles, Czechs, Slovaks, Balticles, etc...) use a 20-5 clean aggregate as a sub-base (or as the upper part of a sub-base structure), but it's not quite the same as a pipe-bedding.

Given all the other iffy practices which take place on new-builds, particularly the largely indifferent approach to backfill materials, the use of pipe-bed isn't the worst sin. As long as it's well compacted and angular, rather than rounded, it's probably just about tolerable.

The Brew Cabin

Laying porcelain flags on pipe bedding