The Brew Cabin

I have started laying the base for a new patio measuring 7 x 4 m. Due to an new extension next to the site I was left with a hole 600mm deep over most of the site. This I have filled useing old brick, concrete, gravel etc, however I am still 300mm short of the final surface level. I intend to put either brick or block paving around the edge with Bradstone 'old riven' flags inside.
Question, what should I fill the rest of the hole in with. The local experts advise more rubble, scalpings, compacted grit.
Any thoughts would be welcomed.
Many thanks

If the layer of fill that you've already laid is 'tight' (ie, no voids) and well compacted, then you could lay a 150mm layer of crusher run stone (what you call scalpings) and top that off with 150mm of DTp1 granular material. However, if the fill layer is patchy and 'open', then I'd put down a membrane of Terram 1000 or TDP115, and then do two 150mm thick layers of the DTp1. The membrane will help prevent the subsequent layers of DTp1 settling into the voids, which would lead to settlement on your eventual patio paving.

Thanks very much for that. I have the latter, The old rubble has been 'wacked' a few times but still has largish gaps in between.
Not being into the 'technical' side of this what is TDP115 please. Is it available from any BM?
Great site, lots of help advice and tips. Please keep it going.
Thanks

TDP115 is just an alternative geo-membrane to Terram 1000 - in fact, I can't tell the diff, which may be bcause there isn't any! ;)

Any decent BM will stock one or t'other, or you can buy piddling 10 square metre 'mini-packs' online at the GardenFab website where they sell it as 'Patio Partner'.

Thanks again. Off to the BM tomorrow and see what they have.

Hi Tony
In my part of the world we have 'CLAY' sub-base. At the moment it is dry and hard and this weekend will lay DTP1 150mm thick. Is it best to have the clay hard or is it better to have it wet and soft so the dtp will bed in better. If you compact it when dry and then it gets wet later will I end up with sagging.
You mention using a membrane, where should it go? In my case I have clay, broken concrete/rubble, scalpings and a top layer of grit. Where does the membrane go please.
Thanks


(Edited by flashman at 9:44 pm on April 10, 2003)

I hope I'm not too late replying to this - it's Sunday afternoon, and you're probably halfway through the job now, but I've been away and this is the first chance I've had to get into this corner of The Brew Cabin since I got back.

Anyway, the state of the clay isn't a big issue. It's easier (and a damn sight cleaner) to work on a dry clay, but it make little difference in the long term. Clay does expand slightly when wetted, but, to be honest, you'd need to be a geo-scientist to measure the diff on a typical driveway or patio job, so don't fret over it. :)

Positioning the membrane seems to be a matter of opinion. There's a good case to be made for placing it between the sub-grade (ie, the clay) and the sub-base (what you might call 'hardcore'), as this will prevent the sub-base material sinking into the clay, but then, if you have an open-textured sub-base, as is often the case when relying on a non-DTp1 material such as your broken concrete and scalpings, then placing the membrane between the sub-base and the bedding layer (ie, the sand) will help prevent the sand being washed into any voids within the sub-base, which can lead to settlement.

From what you have described so far, I suspect the clay is fairly firm and the sub-base material should be ok, so I'd probably go for a membrane on top of the sub-base. However, if you have more than enough, you could always double up, and use two membranes. :)

Let me know how you get on and which option you go with.