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Imo, it's always worth making the right mix for the job.
Am I correct in assuming that you want to do foundations around the outside, then have the middle be bare soil to plant into?
Rather than having a slab, and raised beds on top?
Around the outside, maybe dig 400mm down, put in 200mm of compacted MOT, and 200mm of C10 concrete mix.
And put some rebar in if you're feeling extra (it's not that expensive). Just remember that if you put rebar in, it is an absolute arseache to rip the concrete up afterwards.
Though tbh, unless you're really keen for the plants to root into the ground, I'd do a slab!
Yep, correct, the idea is to plant in the soil...
I currently have a square trench ready to go, well... it was late last summer, niw it's a swimming pool for various small animals (yes... they can escape... it's not a death trap before someone complains)
I wasn't thinking about things like compacted gravel / MOT, but to be fair that's not a bad shout. Thanks
Also, regarding not getting a straight answer out of anywhere...Honestly, if you got 4 builders to make plans, you wouldn't get a consensus.
Unless you go down the path of putting down extension grade foundations (taking into account nearby trees, slope, clay type), filling a nice wide trench with MOT and concrete is going to be fine for a greenhouse.
What are the greenhouse plans, out of curiosity? I've always fancied building a wooden one.
So advice from someone who has erected a few garden buildings. Greenhouses included. Particularly on a clay rich soil.
Use the pre mixed high strength stuff:
As the clay dries under the greenhouse it will shrink and you want the concrete to be able.to survive a few small voids. The 40kn stuff has never let me.down.
Also, If at all possible. You may want to drive some stakes (even rebar would help) into the ground before you pour over.
The more work you put in now the better. A solid base will pay for itself in the long run! DM me if you have other questions.
Ok, now this seems like the answer I'm looking for.
I'd not thought of adding any spikes in, but seems like a good idea, it's amazing how much the ground moves and changes.
Thanks
A normal sized greenhouse hardly weighs anything. Digging footings etc seems like a complete ball ache and overkill.
Personally I'd flatten the ground. Paving slab it then build off that. You can even get paving concrete in bags. Slap it on the ground nice and flat, put the slabs on it, then either water with a hose or wait for it to rain. It's basically postcrete for slabs.
However if you absolutely positively must have foundations then the standard mix will be more than enough. The standard mix is 1 2 3, 1 cement to 2 sand to 3 aggregate(gravel etc).
Hell, for something like a greenhouse you could probably get away with 1 cement to, what, 4 sand then add aggregate to suit.
Will postcrete work? For a standard sized greenhouse then, yeah, within reason.
Bit bodgy, but it's only a greenhouse.
It's not designed to be laid in long lines so it may crack.
If I had to use postcrete I would get a shit ton of aggregate, some sharp sand, and add it to the postcrete mix to add strength, flexibility, and try to mitigate cracks.
However it would probably be cheaper to buy a wheelbarrow and rent a cement mixer for the day and mixing up normal concrete, then barrow it through the house.
Alternatively you could dig holes and postcrete. Then build 'stilts' off of the postcrete. Then build off of the stilts, which, admittedly, will take longer but should be cheaper.
It's not really the vertical weight so much as the force when the wind's across it - hell even the empty frame moves around in the wind and needed pinning down.
Good point on the postcrete, I'd not thought of it cracking in longer lines, will give that a miss then.
Yeah, I just don't have the experience to know if a 1-2-3 or a 1-4-? mix is right, or not, but at least you've confirmed it's not something completely different...
Thanks
If you've got wind problems (😏) then the 1 to 4 with aggregate slung in to add strength will do the trick.
I live in Scotland's countryside. Very, very windy at times. As in it's difficult to walk at times type of gusts, and the rain can spend the day going almost sidewards not downwards.
And one of our sheds is built off paving slabs. Now, admittedly, I didn't build and I probably wouldn't have built it like it is, but it's passed the test of time all the same.
What they did was:
Plonk the slabs down. B
Shuttered the sides.
Concreted over slabs to tie it all in and give it lateral strength.
Built the building and screed it down, then built around the bottom of the shed a little bit to stop any sideways sliding motion in the wind.
Wouldn't pass any building regs but it's been up for decades and it's still here.
Edit: you could probably do the above slab way with external self leveling compound, not concrete. Flatten, slab, shutter, self level, wait, build greenhouse and screw it down, put something around the edges of greenhouse to stop it from going sideways.
Good idea on the edging. I won't ignore the advice from a windy Scot!
Why not just put some patio slabs down? Quicker and easier and if you find some second hand probably cheaper too.
I think it would destroy itself. The ground isn't stable as the clay changes so much between wet & dry, so I'd be laying a large base under the slabs... in which case... no point in the slabs 🙂
I don't know the answer to your question but B&Q have quite a few DIY guides/videos on their website, looking there might help.
Ah, good point, not thought of that. Thanks