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This years big project is to get the old shed (a brick/block pigsty, quite literally) replaced with something waterproof and better looking.
So far the favourite idea is 2x4 treated studwork all round, OSB inside, some kind of cladding (shiplap or loglap or whatever mrsmonkfinger wants nearer the time) outside with 18mm ply / felt pitched roof. Total size about 4m x 4m. Very likely with a 1m porch on one end, so 5m x 4m really. I'm happy with the woodwork side of things.
What I'm less sure of is the concrete base.
Crucially, we already have a (messy, made in several different stages and levels) slab under the existing shed, and its more than large enough, but some of it is lower than other bits and as mentioned its been poured in a number of different goes as and when the previous owner decided to tack another bit onto the pigsty.
Can I just pour over the top of the existing base to bring up the low levels and tidy it up?
Would I need some sort of ties to hold the new concrete to the old (maybe some studs made from rebar) to prevent cracks?
Will I get any weird chemical reactions with the new concrete on the old concrete?
Thanks in advance stw hive-mind
If the levels are not wildly different you could board around the edges and fill with self leveling compound.
I've got about 4 or 5" to make up at the worst points.
If the base is solid could you not leave it as it is and make up the difference with the woodwork? Would be a bit of a pain if you were buying a kit form shed but as you're building from scratch it should be fairly easy.
What is the least difference you have to make up. It's thin Concrete you need to worry about more. You can get away with thinner layer by using epoxy cements and bonding (not sure of details) but it is expensive.
Put some concrete slabs at the corners and where needed elsewhere to provide support. You don't need to add another solid concrete base if the existing base is sound. This sort of thing (lets air circulate too)...
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This is the issue. 4-5" is fine but less than 3 and you really need to be adding something to the mix. I use SBA. Clean the existing surface, brush a slurry of cement and SBA over the surface then pour concrete with SBA in it. Should stick together. That said for a shed base I'd probably just make it up with some slabs on mortar wherever the joists are sitting. EDIT ^ thatWhat is the least difference you have to make up. It's thin Concrete you need to worry about more
Sorry, bit of a mistype in the last post.
It's a 4 or 5" step from the highest level to next highest level, then as I keep going towards one end of the shed it gets lower still (and a bit rougher and quite possibly thinner).
So if I read that right, if I can do one thick layer (of at least my 4 or 5"), I'll be alright with pouring on top?
If the base is solid could you not leave it as it is and make up the difference with the woodwork?
I thought about that, but that would mean putting up with the odd step in the middle of the floor, or doing a suspended floor or something. It seemed like it might be just as easy to level the base off with new concrete.
Put some concrete slabs at the corners
Sadly we got the existing base already, otherwise I'd be right there with strategically placed slabs.
his is the issue. 4-5" is fine but less than 3 and you really need to be adding something to the mix.
Awesome. Sounds like we're good to go with plan A then.
I'd say so. Have at the existing base with a sledge hammer to compact down any loose bits and reveal and hollows then pour away. Give it a clean and a sweep first, too. Giving it a bonding layer of SBA/cement slurry will still help, though, but not essential at that thicknessSo if I read that right, if I can do one thick layer (of at least my 4 or 5"), I'll be alright with pouring on top?
cool
many thanks guys!
could you retain large parts of the existing structure? demolish what you don't need, add some new blockwork, new roof, cast/ make up the slab use some 1" mesh. Then over clad with a breather membrane and some timber cladding.
would be far more secure than a timber shed.
Existing structure is a mishmash of (fairly badly built) thermalite, breeze, brick, bits of fence panel (!) topped with an asbestos roof in parts, cracking corrugated plastic in others, with mainly rotten timber, I could go on. It's falling apart and there is literally almost nothing worth salvaging.
Appreciate the security suggestion. I may yet go with rendered blockwork + internal insulation for the walls - jury's out. TBH it doesn't make a huge difference in the end result or budget.