The Brew Cabin

Hi, no matter how many times i read the info on scredding bedding sand for block paving, it doesn't seem to click.
I have already started a project, a driveway. i have already laid the hardcore base and laid paviours around the perimeter of the site, and haunched with concrete. all i need to do is figure out the scredding process.
I have seen that you prefer the pre- compacted method but i have been told, what you call the hard way screeding without compaction.
The method i have been told is to lay sand within the inside of the edge courses and set up a notched timber method where you screed the sand to a level where the blocks lie 10mm higher than the required level, but when all blocks are laid, compact the lot down to the right level.
However what i don't understand is if you lay sand within the edging courses to a level higher than the required, lets say, 10mm below the finished level, and whack the lot, ie the pre compacted method, then screed off to the required level, so that the blocks lie above the required level. When you come to compact the blocks they won't go down as the sand is compact underneath.
This is my worry.

Hope you can help

Thanks

Liam James

The method we prefer, and the one that is used by most professional contractors, is actually the Partial pre-compaction method. This relies on the bedding material being partially compacted, with just a single pass, or two, of the vibrating plate before screeding to a level just a few mm higher than the required Finished Pavement Level (FPL).

If you use the non-compacted method of screeding, then you may find that, when it comes to compacting the laid pvers, you achieve 10-15mm of compaction, whereas with the Partial pre-compaction method, the pavers may be only 5-9mm higher than FPL.

However: with the uncompacted method, we find that some areas of the sand are naturally more compact, even without the benefit of the vib plate, and so you end up differential compaction and with an undulating surface.

The partial method is intended to compact the bedding sand to an equal degree, but not so much that it would not consolidate further. Experience shows that, after laying, the blocks will compact down to within 2 or 3mm of FPL. Understanding how much to partially pre-compact, how "high" to establish the screeded bed, and how much compaction wiill be achieved with a given sand, a given block and a particular size of vib plate, is all part of the art of block laying. :)

Does that make it any clearer?