Screed Floor - Quantities of Sharp sand and Cement

[steveharr]

Hi,

I am wanting to lay a screed floor that will be 50mm depth and 3 X 4 Meters area.

Can someone please advise me on the quantity of Sharp sand and Cement that I will need for the job assuming that a ratio of 4 : 1 Sharp sand / Cement is correct.

Can I get this sort of quantity delivered (readymix)? And what would be the economical to do so??

Cheers Steve.

 

[TexMex]

3 x 4 x .05 = .6 cubic Metre Sand (about 750Kg)

For a 4:1 mix
Cement would be a quarter of this volume ie .15 cubic Metres (which equates to about 255Kg or about 10x25kg bags)

For a 3:1 mix
You would want .2 cubic Metres of cement (approx 340kg, about 14 x 25kg bags.) Only about £12 more expensive than the 4:1 mix!

The sand would be best obtained loose from your local builders merchant.

I don't know if it would be economically viable to get .6 cubic metres of readimix You'd have to check locally. but mixing that amount by hand is not too difficult.

 

[steveharr]

Thanks very much TexMex what a superb answer.

Steve.

 

[masona]

Just to add on, make sure it's a dry damp mix, hold it in your hand, if it hold together that's the right mositure,

 

[steveharr]

Cheers Masona

 

[steveharr]

Can you tell me roughly what the volume of a 25 kg of sand is compared to a 25 kg of cement. Is it about 2 sand to 1 cement?

 

[breezer]

are they not the same, both being 25kg (and same size bag)

 

[steveharr]

They are the same mass but not the same density therefore not the same size/volume.

 

[TexMex]

Sand is actually quite variable. Most of this variability is caused by the different moisture content. 1.25 Tonne per cubic metre is a fairly good approximation. Cement is quite a bit denser at about 1.7 tonne per cubic metre. You will find that a 25kg bag of cement is a tad smaller than 25kg of sand.

Concrete/Screed/Render/Mortar mixes are, invariably, quoted by volume. Therefore, if you ever wanted a 1:1 mix, you'd need slightly more cement (by weight) than sand.

Another point to bear in mind, is that the cement, itself, doesn't actually add to the volume of the final mix. Due to it's fine particle size it simply works it's way into the voids between the grains of sand/balast. For this reason, the final mix (once compacted) generally comes out closer to 2 Tonne per cubic metre.

Hence, my method of approximating requirements, is to consider the filler requied to fill the volume in question, then to calculate the cement to make the appropriate mix.

Coming back to your original question a bag of cement would be approximately 1.25 /1.7 (about 3/4) the volume of a bag of sand of the same weight.

Alternatively, a bag of sand would be approximately 1 and 1/3rd the volume of the same weight of cement.

Just to confuse matters, cement is still available in 25kg and 50kg sizes while sand is usually sold in 40Kg bags, from builders merchants, whereas the sheds generally sell it in 20kg (or even 10kg) bags.

Before you finally order, make sure you check what size bags you're talking about. Not all bags are born equal.

 

[steveharr]

Thanks very much TexMex

 

[biffvernon]

Just step back a moment and ask, Why use cement? You can make a perfectly good floor with a sand and lime. Lime takes less energy to make than Portland cement and absorbes carbon dioxide from the atmosphere as it sets. It is less damaging the to the planet than cement. Cement's greater strength has advantages in certain applications such as airport runways and multistorey carparks but otherwise we really don't need to use it. Come to think of it, we don't really need airport runways and multistorey carparks.

 

[Thermo]

not going on holiday this year then?

 

[Jimbob99]

If you use a small container and your kitchen scales you will find that sand weighs quite a bit MORE than cement - it is denser.

Hence a bag of cement will be bigger than the same-weight bag of sand -- I think we can see this by looking at the two bags next to one another.

Blue Circle and LaFarge both say their cement is about 1.3 tonnes per cube - all searches for density of sand on the Web come up with a minimum of 1.6 tonnes per cube - and my scales, and litre container, agree.

Be cautious of any advice based of bag-to bag ratios - stick with buckets when mixing.

 

[mointainwalker]

Been dead six years then brought back to life.

Record ?

 

[^woody^]

Not only that, but there is a damn screed estimator sticky that has been at the top of the forum since year dot