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Lobster
 
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Default Floor screed: how many bags of sand /cement?

I cannot believe the answer to this isn't somewhere in the archives, but
I'll be damned if I can find it!

I'm about to lay a floor screed (approx 3m x 1.8m area) using a 3:1 mix
of sharp sand:cement, using a mixer. I can easily come up with the
volume of wet mixture I need; but where can I find out the number of
bags of cement and sharp sand I need to pick up from Wickes?!!

Cheers
David

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AlexW
 
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Lobster wrote:
I cannot believe the answer to this isn't somewhere in the archives, but
I'll be damned if I can find it!

I'm about to lay a floor screed (approx 3m x 1.8m area) using a 3:1 mix
of sharp sand:cement, using a mixer. I can easily come up with the
volume of wet mixture I need; but where can I find out the number of
bags of cement and sharp sand I need to pick up from Wickes?!!

Cheers
David


Can you calibrate the mix ...

Based on say a bucket of sand, mix up 3:1 then work out the % of the
bucket the result fills. I think it will be less than a bucket ... say
85% full? You can get an approx sand/cement to volume multiplier then.

Approach may or may not be helpful...

Alex.
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John Rumm
 
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Lobster wrote:

I cannot believe the answer to this isn't somewhere in the archives, but
I'll be damned if I can find it!


How about:

http://www.pavingexpert.com/concmix1.html#mix


--
Cheers,

John.

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Lobster
 
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John Rumm wrote:
Lobster wrote:

I cannot believe the answer to this isn't somewhere in the archives,
but I'll be damned if I can find it!


http://www.pavingexpert.com/concmix1.html#mix


Thanks John, I did try that site but didn't find that table TBH. Using
that it seems that if I make some assumptions, eg that my sharp sand
will be equyivalent to 10mm aggregate for calculation purposes (is
it?!), and if I change my mix from 1:3 to 1:4) and guess my concrete
grade(?!) and slump(???!) I can at least get some figures out... all
seems awfully overcomplicated though!

David

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John Schmitt
 
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Lobster wrote:

I'm about to lay a floor screed (approx 3m x 1.8m area) using a 3:1 mix
of sharp sand:cement, using a mixer. I can easily come up with the
volume of wet mixture I need; but where can I find out the number of
bags of cement and sharp sand I need to pick up from Wickes?!!


Sand has a bulk density of between 1.4 and 1.6 kg/l (T/m^3)As you are
making a mortar, the higher value will apply. The cement fills in the
interstices, so make no allowance for that or the water. Once you have
calculated how many kilos of sand, decide on your mix. Calculating the
cement should then be a doddle.

John Schmitt




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Lobster
 
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John Schmitt wrote:
Lobster wrote:

I'm about to lay a floor screed (approx 3m x 1.8m area) using a 3:1
mix of sharp sand:cement, using a mixer. I can easily come up
with the volume of wet mixture I need; but where can I find out the
number of bags of cement and sharp sand I need to pick up from
Wickes?!!


Sand has a bulk density of between 1.4 and 1.6 kg/l (T/m^3)As you are
making a mortar, the higher value will apply. The cement fills in
the interstices, so make no allowance for that or the water. Once you
have calculated how many kilos of sand, decide on your mix.
Calculating the cement should then be a doddle.


Thanks John, that's the sort of answer I was hoping for! The figure I
calculate is also close enough to the answer I came up with from t'other
John's pointer to the pavingexpert site to give me confidence I'm
ordering the right amount.

Out of interest, and for my possible future use, what's the rationale
behind the following:

Sand has a bulk density of between 1.4 and 1.6 kg/l (T/m^3)As you are
making a mortar, the higher value will apply.


Thanks
David
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John Schmitt
 
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Lobster wrote:

Out of interest, and for my possible future use, what's the rationale
behind the following:


Sand has a bulk density of between 1.4 and 1.6 kg/l (T/m^3)As you are
making a mortar, the higher value will apply.


If the sand is dry it will be 1.6 if a bit damp the sand tends to behave
like brown sugar and tends to "fluff up", hence 1.4. Wet (saturated)sand
has an overall density of 2 because of the water in the voids, however
the actual particle packing is almost exactly as for dry sand. I hope
this is clear enough.

John Schmitt

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Rick
 
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On Tue, 16 Aug 2005 11:53:42 GMT, Lobster
wrote:

I cannot believe the answer to this isn't somewhere in the archives, but
I'll be damned if I can find it!

I'm about to lay a floor screed (approx 3m x 1.8m area) using a 3:1 mix
of sharp sand:cement, using a mixer. I can easily come up with the
volume of wet mixture I need; but where can I find out the number of
bags of cement and sharp sand I need to pick up from Wickes?!!

Cheers
David


I use the volume of the sand. I reason, rightly or wongly, that the
sement sits in the gaps in the sand to "glue" it together.

Rick
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John Schmitt
 
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Rick wrote:

I use the volume of the sand. I reason, rightly or wongly, that the
sement sits in the gaps in the sand to "glue" it together.


Most on-site mixing of concretes and mortars is done by volume. The
readymix (supplied to site in mixer lorry) tend to use weighbins as they
batch from their silos and a water meter to achieve better quality
control. If a bad load goes into a big project, it can turn very expensive!

John Schmitt


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