One last push

[johnboi]

First of all thank you everyone for your help so far.I have got as far as laying the sub base and tomorrow the first lot of bricks and sharp sand are arriving! My question is what level of sand should I use in order to compact and screed.I an using 60 mm high clay block pavers over around 18 m sq.I have read Tony's stuff on screeding and will use his preffered method but what level should I lay the uncompacted sand before a couple of passes of the wacker and then screeding.From the screeding section I read
"To construct a screeded laying course, the bedding material should be spread quite generously over the area to be screeded, and evened out with a shovel or a rake so that it is 30-50mm higher than the level required." also "uncompacted bedding usually compacts by 30-50%. So, to achieve a finished bed of 50mm thickness it may be necessary to start with an uncompacted bed of 70mm or so." To my unprofessional brain these 2 bits of advice are confusing.
Do I rake the sand to 70 mm or to 80-100mm before lightly compacting and screeding. I want to finish with a layer of sand around 50mm compacted so I end up with sub base 50 mm, sand 50mm and block paver 60mm.
I hope I am not asking a too obvious question? I get the impression that this may need some trial and error but any help as usual would be appreciated.
By the way Tony if you read this glad to see your op went ok... you don't know me but from reading your fantastic site I feel as though I know you...long may you continue!

[84-1093879891]

Screeding is a terribly complicated thing to pin down exactly. The way that a sand or other bedding material compacts depends on so many variables that it's totally impossible to give 'hard and fast' rules that, for example, "83mm of uncompacted sand will give a compacted thickness of 50mm when passed over twice by a vibrating plate".

Grain size, moisture content, bed depth, force of vib plate....all of these have an effect on the compaction, and so the only guaranteed way to determine the required depth of sand is "trial and error". If you are aiming for a 50mm thick bed, then spreading the sand to 80-90mm should be plenty - this depth of sand will probably compact to around 55-60mm, which then allows you to screed it off the surplus and so prepare the perfect bed.

There is a new page dealing with the art of Screeding in preparation, but I'm not sure when I'll get it completed. I've quite a few drawings to finish, and some more photo's to source, but, hopefully, when it's finally ready (I've been working on it for the past 9 months!) I'm hoping it will be the most comprehensive guide ever written.

In the meantime, if you follow the advice above, and allow 80-90mm of uncompacted coverage, you should be fine. :)

Let us know how you get on.

[johnboi]

Thanks Tony for your prompt reply. I will aim for 80 -90 mm and see how it goes from there...fingers crossed!