Advice on ballast/concrete ratio

biddy2101

I'm building a shed base 5.4m x 2.5m x 120mm = 1.620m3.
I need to do it by hand due to access issues, the resident teenagers are going to get a lesson in hard garft!!!  I've got 2 wheelbarrows, a hose & a host of other tools, plus my wife who makes a banging cup of tea,
I'm going to be using rebar as well so I am going to do a ballast/cement/ mix - using 6:1.
My question is - how much tonnes of loose ballast vs how many tonne bags do I need & how many bags of cement do I need?
Thanks

williamgriffin

Go for ready mix with the teenagers on the barrows. 

stuart45

You can always use this if unsure.
On-Site concrete calculator. (source4me.co.uk)

molerat

Doing that amount in barrows will at least teach you one lesson - don't try to do it again.  You will end up with a messy uneven mix.  Look up your local mini mix and get a quote. It will be around 40 barrow loads just to move it, way more than that to mix.  As a last resort hire in a mixer.

FreeBear

biddy2101 said: I'm going to be using rebar as well so I am going to do a ballast/cement/ mix - using 6:1.
My question is - how much tonnes of loose ballast vs how many tonne bags do I need

First off, you don't need a base 120mm thick just for a shed. Even heavy duty garage floors are rarely more than 100mm. No do you really need rebar to reinforce the slab... Dig out your base, put a layer of hardcore (crushed brick or MOT1) about 100-150mm thick and whack it down well. For a wooden shed with a timber base, 50mm of concrete will be ample. If you are planning on using the concrete base as the floor, then 75mm is more than adequate.

Second point - A bulk bag is typically 800Kg of sand/gravel/whatever, so when you do your sums, you'll need to take this in to account or run the risk of not having enough. I'd suggest shopping around and getting loose aggregates rather than bulk bags (if you have somewhere to tip it). Loose tipped should work out a lot cheaper.

Final tip - Put one bucket full of ballast in the wheel barrow. Add a quarter bucket of cement and mix thoroughly with a rake. Add another bucket of ballast + cement, mix again. Do this a third & fourth time, then add just enough water to get a damp mix. Work the water in well with a shovel, then pour. It is backbreaking work, and after the third wheelbarrow load, you'll wish you had a cement mixer. Having done two shed bases by hand, I went out and purchased a mixer to do a patio - So much easier.

biddy2101

FreeBear said:

biddy2101 said: I'm going to be using rebar as well so I am going to do a ballast/cement/ mix - using 6:1.
My question is - how much tonnes of loose ballast vs how many tonne bags do I need

Final tip - Put one bucket full of ballast in the wheel barrow. Add a quarter bucket of cement and mix thoroughly with a rake. Add another bucket of ballast + cement, mix again. Do this a third & fourth time, then add just enough water to get a damp mix. Work the water in well with a shovel, then pour. It is backbreaking work, and after the third wheelbarrow load, you'll wish you had a cement mixer. Having done two shed bases by hand, I went out and purchased a mixer to do a patio - So much easier.

I forgot to mention that I do have a cement mixer - doh!!  I wouldn't even entertain the idea of mixing it all by hand - moving the ballast alone will be hard work - that I know.  

Mickey666

I agree with FreeBear, the key is really the sub-base preparation.  I wouldn't quite go as thin as 50mm but certainly no more than 75mm for a shed base.  Might get away with 50mm if a sheet of steel mesh is used (easier to use than rebar), though a few cracks under a shed won't matter, especially if there's a solid sub-base to prevent any subsidence.

This is an excellent website for all things paving and landscaping, with this specific guidance for concrete bases: https://www.pavingexpert.com/concrete

shinytop

I just did this for a shed about the same size. Use the online calculators for quantity.  Digging out was by far the hardest, most time consuming job.  I dug down 200mm; that's a lot of soil to shift.  I got the MOT delivered in the big bags and barrowed it in.  Definitely hire a whacker plate to compact the MOT. I ended up with 100-125 mm MOT and 75-100 concrete. 

I would also recommend ready mix.  Even with a mixer it will be a slow, tedious task and will not be as good a mix.  It might even be more expensive; for me it was slightly cheaper for readymix than DiY.  Remember they will get the materials cheaper than you and you'll be one of several local drops.  Good luck -  I found laying concrete strangely satisfying. 

biddy2101

So after a lot tea drinking & biscuit eating & weighing up cost vs effort vs whinging teenagers - I contacted Mixamate (firm based in London) & they will charge me a minimum of 2m3 = £354.00 in total.

To have 3.5 tonne of loose ballast delivered by a mate was £140 & then the cost of bags of cement would be about £100 plus the reality of moving 3.5t and mixing 3.5t & then laying it gave me "back ache" thinking about it.

So we're going for the Mixamate big pour during half term so I can get whinging teenagers out of their pits and on the barrows, with direction from me and tea supplied by my wife - no brainer.

Thanks for all of your suggestions.  Stay safe guys.

shinytop

I biddy2101 said:

So after a lot tea drinking & biscuit eating & weighing up cost vs effort vs whinging teenagers - I contacted Mixamate (firm based in London) & they will charge me a minimum of 2m3 = £354.00 in total.

To have 3.5 tonne of loose ballast delivered by a mate was £140 & then the cost of bags of cement would be about £100 plus the reality of moving 3.5t and mixing 3.5t & then laying it gave me "back ache" thinking about it.

So we're going for the Mixamate big pour during half term so I can get whinging teenagers out of their pits and on the barrows, with direction from me and tea supplied by my wife - no brainer.

Thanks for all of your suggestions.  Stay safe guys.

I did a very similar calculation.  As an added bonus, my supplier had a long extension on his mixer (oo err missus!) so the barrowing distance was minimal. Make sure everyone has wellies and make up a tamper to level off.  Thanks for the update and good luck!