Hi @Char1991,
This is a pretty big slab of concrete, which will be a mammoth task alone. At 100mm thick, you are looking at 2.8 cubic metres of concrete which will weigh approximately 7 tonnes. When you are dealing with this weight of materials, with a timeframe that starts ticking the second the concrete leaves the truck, I'd strongly suggest you get a helper or two.
With your existing sheds, are they sitting on concrete slabs and your new slab will butt up against them? Or will the concrete run up to the frame and the corrugated sheeting that sits in front of it? If you have some photos of your existing shed's foundations, this will certainly help me offer my best advice.
If the concrete doesn't butt up to existing concrete slabs, I would need to see it to offer advice.
If the new slab will butt up to the old slabs, you can use them as formwork to pour your concrete against, but you will need to allow for expansion. Attaching Sika 10 x 100mm x 25m Abelflex Expansion Joint Filler Foam to the outside of the existing slabs is essential for this.
I have seen a variety of different things used as formwork with 90x45 framing and 100mm fence rails being common choices. You'll want the top of the formwork to act as a height marker for your concrete so you can screed off of it, so look for a material that is the same thickness as your slab.
You'll want your formwork to be well supported along the full length of each side to make sure the pressure doesn't bow the edge of the slab, so you'll need to drive a star picket or timber stake into the ground every metre or so along the outside of the formwork and screw it in place. These Growies 50 x 25mm 450mm Hardwood Garden Stakes or these Jack 45cm Premium Steel Ultraposts are good options.
Once the concrete has arrived, you're on a tight timeframe, so you'll need the right tools to ensure things are spread quickly.
You'll need a d handle square mouth shovel, such as this Saxon Square Mouth Shovel and a Masterfinish Placer Rake to move your concrete around.
To screed the concrete, you'll want the longest screed possible. This Masterfinish 3000mm Screed is a good option.
You're also going to want a long spirit level, at least 2 metres long to ensure everything is falling away from the existing slabs as intended. You can set your formwork as a guide before the pour, but you'll still want a level handy while it is going on to ensure the concrete is falling as intended and there are no low spots that will accumulate water.
Once everything is screeded, you'll need a Masterfinish Telescopic Handle and a Masterfinish Bull Float so you can smooth the concrete without walking on it.
You'll then need a Masterfinish Cement Edger to edge up against the formwork, so you have nice, rounded edges instead of sharp ones.
Depending on the finish you are looking to achieve, you may also need a Masterfinish 16" Masonry Float to get an extremely smooth finish, or a Masterfinish 900mm Finishing Broom for a broomed finish.
As I'm sure you'll see, there is quite a bit to it and you're going to need quite a few tools to ensure things go smoothly.
Let me know what you think and if you have further questions, please don't hesitate to ask.
Jacob
