Concrete Base

[Blackswanwood]

I am putting a concrete base in for a woodshed and will be including a steel reinforcing mesh. The plan is to do my own concrete with a mixer rather than get a ready mixed delivery. Do I need an additive when mixing concrete for use with steel mesh or am I over thinking it?

Thanks

Robert

 

[AJB Temple]

By additive are you thinking fibre strands or a plasticiser?

For a shed base I would not worry about such things. In case you have not done much, you will find that to get a really good mix takes longer than you think in the machine. It's worth being careful with quantities so that you get a consistent mix quality too.

 

[Blackswanwood]

At the back of my mind Adrian I thought RMC used with steel mesh had an additive to inhibit corrosion of the mesh?

 

[Lurker]

Does a woodshed need mesh reinforcement?
Maybe your ideas are more upmarket than mine

Being a cheapskate, I would use compacted rubble, with second hand slabs.
Assuming you have the transport, slabs can be had for little or no money from gumtree/Facebook marketplace.

 

[Mike G]

I am putting a concrete base in for a woodshed and will be including a steel reinforcing mesh. The plan is to do my own concrete with a mixer rather than get a ready mixed delivery. Do I need an additive when mixing concrete for use with steel mesh or am I over thinking it?

Thanks

Robert

No, you don't Robert. The only reason for using an additive would be for frost protection during curing.

Mesh isn't as straight forward as people think. For it to do any good at all, it needs to be on the side of the concrete in tension. If the ground is liable to collapse, then this is the underside. If the ground is liable to heave (clay, tree roots and so on), then it should be towards the top. If you are protecting against both, then you need mesh top and bottom. Being on the centreline is completely pointless as it will do literally nothing at all. However, mesh needs at least 25mm cover (engineers generally ask for 50mm). It is really difficult to achieve 25mm of cover and still have the mesh in the correct zone if your concrete is only 100mm thick. Practically, unless your concrete is at least 150mm thick mesh just doesn't work. You might usefully add chopped strands of fibreglass instead if you are just worried about the bearing strength of the ground, but are only pouring a 100mm slab.

 

[Blackswanwood]

Thanks Mike - very helpful and makes sense.

 

[clogs]

also out of interest,
the waterproofing agent for concrete doesn't like steel.....?
that was what I was told.......?

my new shed will approx 160m2.....I want a 150mm thick base due to loading and ground conditions....
the ready-mix firm wont deliver up my hilly drive.....and the conc pump wont reach from the road....
(read track) so might need two pumps....
so far this looks like it will be done by hand in 2m strips x3m long .....unless I get lucky with another conc firm....
all the fun of the fair......hahaha....

 

[Mike G]

also out of interest,
the waterproofing agent for concrete doesn't like steel.....?
that was what I was told.......?

my new shed will approx 160m2.....I want a 150mm thick base due to loading and ground conditions....
the ready-mix firm wont deliver up my hilly drive.....and the conc pump wont reach from the road....
(read track) so might need two pumps....
so far this looks like it will be done by hand in 2m strips x3m long .....unless I get lucky with another conc firm....
all the fun of the fair......hahaha....

Waterproofing additives are used with steel all the time. In fact, because their role is the prevention of micro-cracks which allow the passage of water, I doubt they're ever used without steel reinforcing. However, once you get into reinforcing and waterproofing, you are into a structural engineer's territory. I'm not sure, though, why you would need a waterproof concrete unless you were building a retaining wall or an underground structure.

Even the most efficient shape for 160 sq metres of base suggests a minimum concrete depth of 270mm unreinforced. 150mm sounds thin to me even for a reinforced slab. I would certainly recommend you employ a structural engineer for a slab that size.

Have you considered hiring a dumper to ferry the concrete to the pour site? You are also going to need to get your ducks in a row with regards spreading, levelling, tamping and floating a slab of that size. Anything above 30 square metres is a challenge for 1 person, and I suggest you are going to need 4 or 5 people, and at least a couple of them need to be skilled.

 

[Doug]

Did this about 20 months ago



This will eventually be a new wood store, it was all mixed by hand





It’s around 4” thick & I incorporated reinforcing fibers like this

https://www.amazon.co.uk/Build-Colour-B ... 86206&th=1

It went down surprisingly quickly considering there was only me & my lad doing it. Its held up really well considering all the materials for block paving the drive were stored on it last year, quite a few tons of stuff & it’s showing no signs of cracking.
I can’t imagine there will be that weight in timber when I finally get round to constructing the wood store but unfortunately the GLW wants a garden room building before I can get round to finishing it.