The Brew Cabin

i am now using some 3 metre box sectional 10 gauge 2x1 aluminium lengths which are perfectly straight however my concern comes when i lay them on the subbase and cover with 2 - 3 inches of sand i then use the compacter plate over the sand and the bars, this is the problem for me how do i not bend or damgage the bars with the wacka plate when compacting the sharp sand prior to screeding??

Don't run the Vib plate over them! We don't set the screed rails in position until the sand is semi-compacted and we're ready to screed.

If you need the rails in place as a guide when sand placing, then do so, but remove them before compacting and re-set them once you're ready to screed. If your sub-base is accurate, then you really shouldn't need the screed rails in place as a guide - best to leave them out altogether until they're needed for screeding.

ok i kind of understand but what is the best tool for clearing out a channel in the compacted sand to place screed rails back onto mot?? so screeding can then commence with the compacted sand?

(Edited by suki at 5:31 pm on Aug. 6, 2002)

A Brickies' hammer.

Spread and compact your sand, then scutch out a channel for the screed rails in the sand (not necessarily all the way down to the sub-base). Set the screed rails in position, check for level and adjust as required.

Once the screed rails are set correctly, screed of the bedding layer, remove screed rails, tittivate the channel as required and lay them blocks! :)

i am slightly confused when u say not to take sand all the way down to the SB as i have 2" exactly screed rail i i need 50mm of screeded sand so i would in this situation need to go down to the SB or i would have too much sand??. ideally i would compact the sand to about 2.5 inches all over and drop in the 2" rails into the sand on top of the SB and then screed off the excess .5" sand leaving me with exactly 2" to lay the block onto???

If you have a screed rail the same thickness as the bedding sand, then, obviously, you'd need to place it on the sub-base, but, if you were using the rail t'other road round, so it's only 25mm deep, then it wouldn't need to go all the way down to the sub-base.

Remember, not everyone uses 50x25mm screed rails - some are only 25x25 or 40x30.

i understand exactly what u are saying tony but how do i know when using the 25mm x 25mm rails that they have axactly 1 " of sand is underneath them to the Sub baseand that the 1" is square along the lengh, these are things that i wish to learn, although our jobs are tip top and we get all our work from word of mouth i see u as the daddy of paving i wish to learn from your vast knowledge so plz do not see me as questioning what u are saying as i know u have massive knowledge and what u say is correct i am mearly trying to glean as much info as poss :) from the master ;)

You shouldn't set the screed rails to a level of x mm above sub-base - they should be set to x mm below finished paving level (FPL ).

Now, just how you determine the FPL at any given point is up to you. You could use an automatic level of some kind, or rely on boning rods, a taut string line, a laser, or whatever, but levels for ALL layers, are judged from FPL, not from the level of the preceding layer.

So, with the 25x25 screed rails, they might be 25mm above sub-base at one particular point, but they could be 30mm halfway along their length, and 35mm at the far end, if there was a 10mm difference in your sub-base. Remember that working tolerances decrease the closer you get to the paving layer. Your sub-grade can be +/- 50mm, and your sub-base +/- 10mm, the bedding +/-7mm, but your finished paving should always be +/- 3mm from FPL.

And less of the brown-nosing! ;)

ok i got it now i do it a little different to that and i seem to do ok but i,ll give it a try like that and see what happens, heres a quicky for ya , when we are working on site and one of the labourers drops a fag end on the sub base the norm responce is no where on AJ,s site does it say that fag ends is a suitable part of the sub base now pick that out and throw it in the skip, your site is a frequent talking point on the job im afraid, brown nosing apart it is excellant :)

Fag ends, the crusts off bacon butties, and unwanted copies of Juicy Lucy and her Triangular Monster with all the pages stuck together do not count as acceptable sub-base material, I'm afraid. ;)