Fitz wrote:
I've been googling for this but I seem to have lost my mojo.

I'm going to be laying a patio soon and plan to use a 75mm layer of
compacted dtp1 on top of soil. Then bedding layer and then flags.

The thing I can't seem to find is any indication of how thick the
uncompacted layer of dtp1 should be so that after the appropariate
number of passes with a whacker plate it compacts down to ~75mm.
Shoudl it be 80mm, 85 mm, 150mm or what? I'm not after millimeter
perfect I just have no idea how much this stuff will compact.

I've ben using the excellent pavingexpert site and I have a horrible
feeling it will say somewhere on there, but I havn't found it yet.

thanks in advance

It doesn't go down very far so don't go berserk with it!
If you want to put down 75mm and then whack it this is perfectly adequate,
although for a patio it's probably not required at all considering it's only
taking foot traffic....I use 100mm compacted for drives, with a 50mm bed of
grit and then block pavers or flags and I've never had one sink yet, even
those who have 2 or 3 large Mercs, although I don't use a whacker for this,
I use a vibrating roller - that *does* take it down! - it pulverises it into
the subsoil and if it's wet you can get a finish on it that you could mix
sand & cement on with a shovel and not get any stones in it.

For a patio I would use only an inch or two, just as a firm base for your
sand/cement mix, to get 50mm all over (prior to whacking) use
trammels....two lengths of 50mm timber down each side, fill in with
hardcore, then run a trammel (another length of straight timber) across the
top of both (like a letter H)so that the thickness is even and the surface
is fairly flat, then whack the lot a few times, you'll notice dips and
lumps, fill in the dips with finer grade stuff or grit sand and scrape off
the lumps and whack again, you don't need to get it like a snooker table,
but the flatter you do get it, the easier the flag laying is....use a
stringline for your flags and lay them on 5 big blobs of grit sand and
cement (no plasticiser or any other additives), for getting the blobs equal,
I normally use a 3 inch plant pot and they come out like little uniform
sandcastles!....a couple of *taps* with the flagging mallet and they are
done, don't walk on flags for 12 hours after laying.


HTH