How to build a cement base for a garden shed?

ashp

Hello Experts,

I'm new to DIY in general. The most I have done is assemble flat pack furniture and do odd fixes around the house like filling a hole in gyprock or drilling a hole in brick.

I want to take up a proper DIY task and get a garden shed on the side of our house so i can put all the gardening tools in it and clear up space in my garage. I have read various posts in the workshop and planning to follow this post to build a cement base for the shed (1.5mx0.78m).

Additionally, i have some space in the corner of our backyard which i plan to convert into a multi purpose deck (2mx2m). Thinking of putting a cement base for that space as well before i put a deck. 

For both places i have the same question: How do i build a cement slab in a corner? How is the frame built for that?

Also, do you think it would be wise to take up task to build a 2mx2m cement slab by myself? I checked on some online calculators and it requires .36 cubic meters of cement or close to 40 cement bags. I'm optimistic that it can be done but need wisdom from more experienced members 😀

Any guidance is appreciated 🙏

Sharing the photo of side where I intend to put the shed as i have it handy. 

cheers - Ash

JacobZ

Hi @ashp,

A warm welcome to the Bunnings Workshop community and thank you for your question.

I'll start by saying that if you are planning to build a deck, there is not a lot of benefit in pouring a slab for it to sit on. You are better suited, simply digging pier holes to set posts in so that the deck sits over the natural ground. The number of materials, amount of labour and difficulty are far less than pouring a concrete slab yourself. While it would be possible, unless there was another reason you wanted to have a concrete slab, I don't see a benefit to it.

The smaller slab is much more achievable, only requiring around 10-12 bags of concrete, which is certainly much more manageable alone.

You would build your formwork using 90x45 H3 framing timber. Cut it to length, set it in place, then drive Jack 45cm Black Premium Ultraposts into the ground along the length of the formwork. You'll then use a spirit level to lift the formwork so that it is level on the outer edge and very slightly sloping away from the house. When you have found your levels, drive a screw through the pickets into the timber to set the formwork in place. You should aim to have a picket roughly every 600mm along the formwork to ensure it can support the weight of the concrete pushing against it.

On the house side of the slab, the brick will act as the formwork, however, you will have to apply this Abelflex Self Adhesive Backed Expansion Joint Filler Foam to the wall prior to pouring your concrete. This foam will create a barrier between the new concrete and the wall which will allow for expansion and contraction of the slab.

For a small slab like this, you should add some Jack 1800 x 1050 x 5mm Light Duty Reo Mesh, cut to size with some bolt cutters. You can pour half the concrete, set the reo mesh in it, then pour the rest of the concrete over the top. You need to ensure that the mesh is in the middle of the concrete and is not touching the ground or poking out the sides anywhere. This can be done with reinforcing bar chairs, but for a small slab, it is pretty easy to do without.

As you will have set your formwork to have a slight fall away from the house, you can use it as a guide to screed the concrete using a straight edge like a spirit level. Once your concrete is screeded, finish the slab with a Concrete Float and tidy up the perimeter with a Concrete Edger.

There are a few steps to the process, but a relatively small slab is manageable by yourself. You might like to give it a try and have a think about what you want to do with the 2x2m slab and whether you'd like to or not.

Let me know what you think and if you have further questions, please don't hesitate to ask.

Jacob