# Forum Home Renovation Concreting  type of sand under slab

## barney118

I was wondering the type of sand I should use under a new slab pour. I need to get some sand for mortar and was wondering if I should just use this, I understand that this has some clay in it compared to other types. 
Cheers Barney.

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## cherub65

Just use fill sand, cheaper

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## barney118

My thinking is save on delivery as I will need a T for brickwork I may as well buy 3 t all up for screening.i would assume brickies sand would compact harder too?  
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## cherub65

Won't charge more if you get on same load. Brickies sand doesn't compact better as it has a higher clay content

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## Bloss

Simple answer is it doesn't really matter - once the slab is in place the sand can be washed away, it's effectively the formwork for the base! But as Cherub says most places will do mixed loads so you could save some money by getting the part load of brickies sand which is 'fatty' and the 3m of washed sand or even roadbase for the fill. Depends where you are, but brickies sand around $95-$110 m3 and fill sands about $10 a m3 less - so not much of a saving, but roadbase/ fly ash or crusher dust can be half that amount or less. So my suggestion is get some prices before you order.

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## barney118

My brother in law is a concreter and he is saying use crusher dust as it compacts better, but there are pipes in the concrete so I believe that doesn't matter, slightly off topic I believe I can have 50 mm concrete over the top of the pipes in this bathroom?  
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## Bloss

crusher dust is cheaper too

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## intertd6

> Simple answer is it doesn't really matter - once the slab is in place the sand can be washed away, it's effectively the formwork for the base!

   this would be true for slabs with close internal beams but with a normal slab with just a perimeter edge beam then the the slab supporting fill is very important for permanent support of the concrete & when you think about it it would be really hard for a 100mm slab with one layer of F72 mesh to span say 10 meters unsupported.
regards inter

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## Bloss

Not suggesting otherwise, but there is little likelihood in the vast majority of cases anything except a small area of collapse of the fill if the area has been compacted ie: result could be fractions of a m2 or even 1m spans unsupported not 10m.  Real life not theoretical possiblities. We are talking about a garage slab here too - not a residence. In any case read my signature . . .  :Wink:

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## barney118

Sorry Bloss, the pour I am talking about is going to be an infill slab for my bathroom laundry to start with. It's a room 5.1m long x 2.5m wide I removed the existing infill and I am on clay which is as hard as rock and dry. The brickwork is single leaf engaged piers on 400x 250 strip footings which appears to have 2 layers of mesh, no DPC in bricks or membrane on the stri footings. I was originally getting sub floor water in here, but I have put that down to the backfill on the side wall upto 600 high that I have since removed. The plumbing is just complete for the sewer do I now need to work out my slab height etc. The pipes are 100 mm and they are under the strip footing on one end and level with the top of the pipe at the 5 m end, fall of 100 mm over the floor.I am looking at filling inbetween the pipes to level ..... And concreting over the top of the strip footing by 90-100 mm leaving a gap between the bricks the thickness of form work. I will lay a membrane down and termite stuff (detail to follow). I haven't ruled out removing the brickwork (where windows are) and pouring the slab to where the bricks are now and inserting dpc and termimesh, which also allows more options for windows etc. I will join the metal lintle by welding, paint etc and rebrick.
Phew that took some effort!
I have plenty of height above, what is the minimum height slab I can put down? Over the pipes, they ok to be encased here?
http://www.renovateforum.com/attachments/f205/91596-bathroom-laundry-critique-please-bath2.jpg picture. 
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## Bloss

Ah well now I know eh!   :Redface:  For some reason I confused this with another post which had a pic - and was for a shed. In any case crusher dust is OK. Inter is right on this one - you should be building to a spec, not guestimating . . .

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