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Posted: Sun Dec 10, 2006 8:11 pm
by Skan
My contractor is doind some work for me and they had excavate to the required level, they pour concrete on the ground(blinding), install timber formwork, install the steel bars and pour the concrete.
Why do we need the concrete blinding?
What does it do and how does this come about?
Do you pay the contractor for the concrete blinding too?
Why some concrete work require the concrete blinding and some don't?
Posted: Sun Dec 10, 2006 8:15 pm
by Ted
Skan wrote:My contractor is doind some work for me and they had excavate to the required level, they pour concrete on the ground(blinding), install timber formwork, install the steel bars and pour the concrete.
Why do we need the concrete blinding?
What does it do and how does this come about?
Do you pay the contractor for the concrete blinding too?
Why some concrete work require the concrete blinding and some don't?
Why do we need the concrete blinding?
You blind the compacted hardcore with sharp sand or ballast to get a nice level surface for the slab to sit on. If the base for the slab is noce and smooth it means that when the concrete moves it does not crack, otherwise part of it may be held in place whilst part of the slab is moving away, thus creating forces on the slab and subsequently cracks.
A contrcator can't charge much for blinding; it takes pretty much no time and costs a tonne or two of sand. Basically a slab should always have a hardcore base and this should be blinded. \Foundations and footings often don't need this.
Posted: Sun Dec 10, 2006 8:21 pm
by seanandruby
it gives steelfixers? chippies a good clean level surface to work on. also we put a membrane under the blindig. the moisture wont be sucked out by the soil.
Posted: Sun Dec 10, 2006 8:23 pm
by lutonlagerlout
are you sure its "concrete blinding " skan ??
they might use lean-mix concrete for this application which is ok
but i cant see the point of them using expensive concrete for blinding
ask them,communication is the key to sucess
regards LLL 
Posted: Thu Dec 14, 2006 7:33 am
by Skan
Hi,
What are the differences between lean mix concrete and concrete blinding? As far as I am concern, it is concrete and they mentioned that it is concrete blinding.
Posted: Thu Dec 14, 2006 5:58 pm
by lutonlagerlout
it is probably crushed concrete which is suitable for a sub base,we were using it yesterday and today and it works fine
it could be lean mix concrete which will go hard as well and is also fine
you need to talk to your builder more mate,hes the one doing the job,but remember he will do what he has quoted for
LLL
Posted: Fri Dec 15, 2006 7:38 am
by seanandruby
personally i wouldnt be questioning the builder. the fact he is using blindig proves he is a pro. imagine if there wasnt any blinding, then the dig could be unlevel, muddy the steelwork would then sink, you wouldnt have cover on it causing it to erode, thus causing concrete to fail. blinding isnt structural, so it can be semi dry then wackered , or, piss it up make it easier to level. but it is very important to use it where necessary. on my job we dig, terrain, place 300ml of 20ml stone for filter drains ( about 200 tons a day) then membrane then blinding then 900 deep steelwork and mass pour with concrete. maybe 2, or, 300 cube per day.