The Brew Cabin

I excavated about 50 sq M down to about 10 inch -
its not easy getting down exactly 8 inch ! I've backfilled
with 20 mm Limestone where the concrete edgestrip will go to bring back up a couple of inches to 8 inch
and so save concrete.

The concrete strip will be 12 inch or so wide - I've not
provided for any steel reinforcing as I figured it would
be OTT. However there will be some damaged but new 4"x4" X 7' 9" concrete posts (I had left over from a previous job) laid in the trench.


I've broken up the very heavy concrete flag stones
(typically 6" x 4" and 2 1/2 inch thick ) that used to
form the driveway and will put them down with
6 " Dtp1 over top.

I will be using blocks on top of the concrete strip as edging and presume to get the slope I simply bed
the bricks at one end of the drive on more
concrete than the other end ! The drive is 8 metres
long and I'm going for 10 mm per metre slope on the edging strip.

Any advice would be appreciated - including what proportions to use in the concrete mix.

On a 8m x 6m area at 6 " deep I figured 1 1/2 cub
metres of concrete would be needed and was going
to do it by hand - is this stupid ar anything else
I've said not that smart ??

Cheers

Fatcat

p.s. Am I supposed to mix inches and metres 'cos
can't work any other way !

Have you read any of the Block Paving section?

This gives full details on sub-bases, edging courses, concretes and everything else you could need to know for a typical block paved driveway.

10mm fall per metre is not adequate - you might just get away with it, but at 1:100, even the slightest deviation from line will result in ponding. You need to be nearer to 1:60 fall.

Also, you don't generate falls by increasing the amount of concrete beneath an edge course. You should regulate the sub-grade or the sub-base so that the concrete bed is a fairly uniform depth. If, for example, you find that at one end of the job you need a concrete bed that is 150mm deep and at the other it is 250mm deep, then you'd use some sub-base material to make up the difference so that a uniform bed depth of 150mm could be used all the way along that particular edge strip. Having said that, 150mm is a touch excessive for a residential driveway, unless you're using really heavy vehicles. For 99% of driveways, a bed depth of 100mm of concrete is plenty.

Read the pages quoted above, and if you still have questions, come back here and post them.

Had trouble with your web site but looks like
it was AOL browser playing up (not unusual).
can read nearly all web site now including
actually seeing the pictures !

I still can't get the hang of how the levels are set.
I've seen the pic showing how a strip of wood is
used to level the sand by running over the top
of the edging strip. O.K.

The edging strip will be set on a concrete strip
that itself rests on the sub base. Now my simple electricians background tells me when you run
concrete in a trench it ought to settle at the
same level all the way round ! i.e. roughly
horizontal.

If you alter the gradient of the sub base to 1 in 60
then how do you maintain that gradient when you
lay the concrete strip on top ?

Got me beat. Maybe I should stick to wiring industrial units !

Concrete will sort-of settle to level if is it sopping wet, but that's not the type of concrete we want to use for bedding edgings, edge courses or any other paving units. We use a semi-dry mix, which is relatively stiff, or 'low-slump', and is capable of maintaining gradient of greater than 1:1.

All this is described in great detail on the main website. Get rid of the silly AOL comedy-browser and you should be able to view the entire site in all its glory.

Thanks for info I've been through the (brilliant website)
umpteen times and think I'm sort of getting the idea !

One question though. Setting the sub base gradient
for the edging correctly is one thing but I'm worried about setting the gradient over the rest of the area
to be paved - which is around 8m by 6 m. With the edging strip set is it ok to rely on the bedding sand
to compensate for any diffences in gradient where I don't quite keep it uniform or am I going to eventually encounter some settlement problems ?

No - you should never vary to the depth of the laying course to compensate for inaccuracies in the sub-base or to create falls. The sub-base should be formed so that it matches the required profile in terms of falls and levels, and should be accurate to ±10mm.

If you use a variable depth laying course, you end up with differential settlement.