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Posted: Sat Jan 13, 2007 11:21 am
by TheVictorianCobbleCo
Question. Where I'm working, a new bedroom floor is going in over an old existing concrete floor. The guys doing it have laid building sand hand compacted to level, then about 2 1/2" insulated polystyrene type sheet, chicken wire over to bind, and then 3" - 4" cement/sharp sand screed, in a quite dry consistency. My question is - is there an engineering reason for the thickness of the screed, or will it do as well to do a wet concrete mix for say 3", let it dry, and then do a 1" damp screed of sand/cement to finish? I've not seen it done this way before (coming from outside the UK) and just want to understand the logic. Thanks for any input.
Posted: Sat Jan 13, 2007 12:16 pm
by lutonlagerlout
hi bill
that is the way we do it here mate,
normally screed is only specified as 50mm thick ,the main reason for screed is that it gets the floor really level, and because it is quite a dry mix you can do a lot more than with a wet mix in a day
its very difficult to get a wet mix as flat and level as a dry one
the guy we use has a pump/mixer ,1 guy knocks up and 2 lay and they did 55m2 in 50 minutes for me the other week, and its all spot on.
he reckons some days if they have a run 3 blokes can do 5-600 m2 a day,thats a lot of screed
cheers LLL 
Posted: Sun Jan 14, 2007 9:46 am
by TheVictorianCobbleCo
Thanks, I appreciate the response. At those volumes the guys obviously know what they're doing. Way out of my league. For those areas would they have to include expansion/crack joints, or because something generally goes on top, theres no problem?
Posted: Sun Jan 14, 2007 10:05 am
by seanandruby
try screeding one inch of screed is a nightmare. if you placed the concrete higher you would still have hills / valleys in it and at the high points the screed would be even shallower, so there would be no strength and it would fail. 50ml is easier to screed and trowel up. ask me to screed 25ml and i would walk away. on my job thousands of metres are done each week all we do is shutter 50ml, then the screed is pumped self leveling. we do the smaller rooms the old way. its all down to tolerences, strengths and the good old tried and tested methods. hope this helps?
Posted: Sun Jan 14, 2007 10:18 am
by lutonlagerlout
TBH bill i have never seen anyone use expansion joints on screed,it may be specified on larger jobs but i have never seen it
and as sean says 50 mm is the ideal screed depth,i have done s5 mm screed but only when i knew flooring was going down as soon as it was dried out,proper pain .
cheers LLL
Posted: Mon Jan 15, 2007 3:50 pm
by TheVictorianCobbleCo
Thanks all, appreciate the input, and it all makes good sense.
Posted: Wed Jan 17, 2007 8:23 am
by simeonronacrete
If you use Ronafix (liquid) with your cement:sand screed you can lay a screed with a minimum thickness of only 38mm on to polystyrene.
Your screed would be 1:2.5 cement:medium sharp sand gauged with 1:3 Ronafix:water.
Give Donna or Daniel a call on 01279 638 700 if you want more information.