[Closed] Extending a concrete base for a cabin

I did this by shuttering off the extra bit level with the slab already there. I then drilled some big bolts for concrete into the edge of the old slab to give the new section something to ‘bind’ to. I then just added some hardcore and poured the new bit of slab. Worked for me.

Dowels for sure.

Ok. so the plan was to extend the base, using some rebar and ready mix.

I only need a narrow strip and estimate its 2 bags of ready mix. Should be easy right?

So, there appears to be a national shortage on the stuff, no where I've looked has it in stock.

Could anyone suggest any alternatives? Possibly I could mix the stuff myself but I imagine getting hold of the seperate materials is also a challange and its only approx 0.2m3 so getting a lorry to delivery would be way over the top....

I have 3 weeks and counting!

It's cement that in short supply. My local builders' merchant was limiting it to 10 bags per customer, but you'll only need 3 bags for 0.2m3

For 50cm I wouldnt bother with rebar.

It's cement bags that are in short supply, try your local wholesaler and take your own bag for dry mix

I’d read it was a good idea to tie the bases together, I’m not fussed about it cracking as it’ll be covered by insulation and a floating floor, but I don’t want it to subside from the main slab

Dug a hole to check the depth of the existing slab, it’s 20cm deep. I had planned on a 10cm slab. Not sure now, should I match the existing one? Means more materials

Soil is clay and there is a little bit of seasonal movement as the house has small cracks that reappear

With health and safety nowadays I can't imaging being able to walk into a factory with Asda bags for loose cement, it's one of the worst stuff ever to transport unless in its own bag, all that choking dust and the back of the Octavia getting hoovered for the next few hours
Cement is still available but like bog rolls and pasta last year greedy gits bulk buying

For 50cm I wouldnt bother with rebar.

+1

Assuming it's a flat base, or even spread of runners, the base of the cabin will spread the load and 90% of it will be on the original slab, so I can't see 50cm at the edge moving much (unless you really screw it up).

I think I’d hire a cement mixer and have a go at it myself. Just start buying up cement ASAP - I’ve recently had to lay a patio and had to buy materials from various suppliers - then realised Buildbase sells to the public and I could have got everything I needed from there.

For the sake of some metal dowels being drilled into the existing base I’d just do that for peace of mind.

The design of the cabin means there is no floor or base, you fit a floating floor later, so that means all the weight goes through the walls rather than spread across the whole base. Is my understanding, the new strip will support the front wall with the doors so I’m keen it doesn’t budge as I don’t want to be trying to sort sticking doors if I can help it

Think I’ve found somewhere with some cement so will be buying some ASAP £15 delivery is almost as much as the cement itself….

I would definitely put some mechanical connection in the joint. Otherwise if your new slab settles the cabin walls will distort. 20cm sounds about right, so your 0.2m3 is 0.4, but probably not enough to justify the hassle of hiring a mixer, cleaning it out, etc, compared to mixing on a board with a shovel.

The cost of the bar is minimal and it’s just half and hour with a big drill so I think I’ll do it for peace of mind

Ive not worked out this before, so 5m x 0.5m x 0.2m is 0.5m3

So, this is approx 6 bags of 25kg cement and 24 bags of the 25kg ready ballast you can pick up. So that’s 3/4 ton of material. Makes £15 delivery not seem to bad….

For those of you experienced does that sound right?

https://www.diydata.com/general_building/concrete_calculators/concrete_calculator_2_m.php

This would suggest I just need 4 bags of cement but loads more ballast.

Is confused

1:6 sounds about right to me, but it's >20 years since I did this kind of thing. Would definitely use some rebar for peace of mind. I'm sure you know this, but £15 delivery means unloaded on your drive, not carried round the back! Prob easier to stick a board on the drive, mix it there, and barrow it round.

Concrete is approx 2400kg/m3, so you should be expecting about 1200kg of materials for 0.5m3. Theoretically bit less because you do add water and some of that is chemically bound into the mix, but you're better being slightly over.

Based on a 1:2:4 mix (cement;sand;coarse aggregate) that's 7x25kg cement, 14x25kg coarse sand and 1x800kg bag of 20mm limestone. It's much cheaper in 800kg bags than 25kg, although if you're carrying it from the front to the back you might prefer 25kg as it avoids shovelling it into a barrow.

Thanks for the advice guys, going to take a punt, would rather have too much material than not enough to finish the job!

Volumetric concrete mixer, pay for how much you take there are loads going about now

Best of luck, I've got a Tuin as well, had it for a couple of years now, 55mm wall thickness, it's superb, has really added to the house. Mrs isn't really one to spend much time in the garden, but she loves this place. She's started a new job that's bloody stressful and really full on (NHS Stroke rehab), it's became her wee enclave of peace and quiet.

Enjoy.

Sds drill and some threaded bar. 10mm or 12mm, dril it maybe 10mm in, chem fix the studs in place.
Tgen shuttering and either mix yourself or get a price for mixed on site (axtel) where you pay for what you take.
You might need to find a place to shoot it to if the lorry is out front and the shed out back
Otherwise hire a mixer and do it yourself, need a barrow and a spaz maybe a poker if you want a real proper job.

Umm 100mm in might be better

Mixing up over a tonne of concrete by hand will take a while, I'd order it from a volumetric mixer if you can. If you've already ordered and paid for the materials, it would be worth hiring a small mixer. Even mixing it in a wheelbarrow is easier than on a board, see

access wise it's really easy as we are a corner plot and the side gate is within 20 metres or so of the drive.

I'd assumed a lorry delivering would cost a fortune especially on such a small volume. I'll check a few companies just for comparison

and I'm hoping the cabin / posh shed will be really nice, it's got to be better than the current state. spent a hout clearing up spilt engine oil dumped by previous owner....its a right state in there