Shed/aviary base

[Jackmcgee]

Hi,

Just looking for a bit of advice / guidance.
I'm build a new shed and aviary. The old shed has already gone and I've doug out ready for the new base. My original plan was to reuse the old slabs for the base to save money. I've done some working out today and I'm really not sure it will be! It's about 3m X 2m so I'll need 2x bags of MOT (wickes £135 + £35 delivery) then a bag of sharp sand plus 7 bags of cement (roughly). Would it be just as easy and maybe cheaper to get some free hardcore off FB then I'll just need 1X ballast £100 inc. delivery & 8 bags cement?
I'm also assuming concrete is stronger/better and is more likely to be OK in 15-20 years?
One other thing as you see the area backs onto my fence so I need a small retaining wall, would it be OK to use paving slabs on there ends? they are 16" by 16" so I was going to bury half of them in the ground on a mortar base?

Thanks in advance

 

[Wayners]

I just paid £40 plus £10 delivery for type 1.
Large bag is 850kg I think.
20kg bags are £3 each so expensive if you want a few..

Loose tip gravel and sand can be cheaper sometimes and local firm can normally deliver same day.
Large bags you might have to wait a few days.

Sharp sand is about £60 for 850kg.

So £40+£60+£10 delivery if you want large bags.

Yeah use paving for edgers.
SBR and cement to make a slurry if you want concrete to stick better


You could use concrete and polished off for smooth surface. Then seal

 

[oldbuilder]

Your base area is 3m × 2m = 6m², so it helps to separate the sub-base and concrete calculations.

If the chosen construction requires 100mm of compacted MOT Type 1, that is 0.60m³. Using 2.2 tonnes/m³ as a planning density gives about 1.32 tonnes before allowance, or about 1.39 tonnes with 5% added. Two 800–850kg bulk bags are therefore in the right general range, although the merchant’s actual bag weight and material density should be used.

A 100mm concrete slab over the same area is also 0.60m³, or 0.63m³ with 5% allowance. At 75mm it would be 0.45m³, or roughly 0.47m³ with allowance. Those are quantity examples rather than a recommendation on the correct construction depth.

One bulk bag of ballast plus eight cement bags is unlikely to produce 0.63m³ of finished concrete, so check the supplier’s stated yield rather than relying on bag weight.

 

[yardcalchub]

To turn the volumes above into actual bags: your 100mm slab over 3m x 2m is 3 x 2 x 0.1 = 0.6 cubic metres, and with a small waste allowance you should plan for about 0.63 cubic metres.

A standard 25kg bag of ready-mix concrete makes roughly 0.012 cubic metres, so 0.63 / 0.012 = about 53 bags. That is a serious amount of hand mixing, so for a job this size it is usually cheaper and quicker to buy two bulk bags of ballast plus 10 to 12 bags of 25kg cement and mix at roughly 1 part cement to 4 parts ballast.

For the small retaining wall by the fence, count blocks from the face size: a standard 440 x 215mm block laid flat covers about 0.44m by 0.225m including the joint. A 2m long wall at 0.45m high needs 2 courses of 5 blocks, so about 10 blocks plus a bag of cement for the mortar bed. Build the wall first so the slab locks its toe in.

A poured slab will outlast slabs on sand as long as you compact a good 100mm of sub-base under it, and keep the shed's timber bearers off the concrete with packers so they stay dry. That is the detail that gives you the 15 to 20 year life you are after.

 

[stevie888]

1 to 4 is way too rich. 1 to 6 or even 1 to 8 for this sort of job.