# Forum Home Renovation The Garden Shed  Slab for a shed, before or after ?

## mterra

Hi guys, I am planning on building a shed/workshop soon approx 10m x 4m.  What's better, building the slab first then the shed, or the shed first then the slab after?

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## TermiMonster

Horses for courses, but my preference would be slab first, it possible.
TM

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## rod1949

As TermiMonster said, slab first.  Set up your formwork square and level then screed off across the 4m wide and it will give a true finished level... easy.  You can even set the bolts (if using posts/coloums). 
If you went the other way shed first then it means the posts/walls would have to set up packed and braced and a bit extra mucking around to pour/finish the slab.  Another issue in doing it this way which doesn't show up until sometime in the future is if you are cladding the walls with any zincalume sheeting and using the sheeing as the formwork then the wall sheeting will corrode due to the reaction of the wet cement at the initial pour.

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## mterra

Hi rod1949, do you mean the sheeting can't touch the concrete when it's wet?  The sheeting would touch the slab in either method.  My main reason for wanting to build the slab after it will be easier to position wiring etc.  My garage was built slab afterwards around 20 years ago.  The sheeting on the garage was around 30 cm above the ground, so my Dad and I made a brick wall from the ground to the sheeting and filled it with concrete.

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## rod1949

> Hi rod1949, do you mean the sheeting can't touch the concrete when it's wet?

  If you are going to clad with a zincalume sheeting then yes that's one reason ie  the heat/curing action of the wet cement effects metal.  And then lets say the cladding is custom orb (corrugated) and is used as the formwork thus the wet cement flows into every corrugation, when the wet cement dries and shrinks away from the custom orb and creates a little gap, with the build up of moisture over time the custom orb corrodes from the back where it been against the concrete.

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## mterra

So as long as the sheeting on the walls is not acting as a form for the concrete building the slab after is ok?  In my garage bricks were used as the form and the concrete maybe covers the bottom of the sheeting by about 1cm.

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## Harry72

Before you set up the pour in the shed coat the exposed tin in a bitumen paint... should see you an extra 20yrs.

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## mterra

Thanks Harry72 that's a good idea!

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## corbs

I have done a bolt on and a pour in.  If given the choice I would go the pour in anyday.  It is water/wind/weed/pest proof.  There is a bit more stuffing around getting it all level in the early stages but no worries with formwork or anything else at the end, just back the truck up and pour it in until you hit your level.  One of those laser levels which give a solid tone when you are on your level are worth their weight in gold for levelling it all. 
Corbs

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## jatt

Yeah Helped build a shed that was clad with colorbond about 5 years ago.
Slab was poured after shed was cladded.  Same deal as previously stated.  Cladding started rusting down the bottom where the slab was poured.  As a result when a mate and I built our respective sheds we put the slab down first. 
Heard of folks using black plastic to protect wall cladding whilst pouring.  Sounds like a pain to me tho. 
What I recon is a good idea is where a "step" is created on the edge of the concrete slab when poured.  Work out where doors are going to go first naturally.   
Whatever u are using as wall bracing (top hats etc..) make sure the outer edge finishes these in a vertical plane with the top of the slab.  The bottom of the wall cladding sits in the actual step.  Harder for the rain to get in. 
Hope that makes sense.  Too bad I saw this after my shed was built.  
Helps keep the cladding out of the dirt.  At least for a while anyway.

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