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How you pour a concrete slab?

Hi all,

I wanted to pour a concrete slab for a garden shed, the slab size is 1.8x2.8m. I'm trying to do it myself and avoid hiring a concrete mixer or getting a concrete truck just for this small area (unless you advise me to do so). I came across this video https://www.youtube.com/watch?v=GC0j2Ey5NNk which I wanted to check with the experts if this is a good way of doing it and is there anything I need to be aware of?

Thanks in advance

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Comments

JacobZ

Hi @ososbg,

Just to start with, if your slab is 100mm thick, you're looking at 0.5 cubic metres which is 50x20kg bags of premixed concrete. Keep this in mind when planning your project.

I have seen plenty of examples of people dry-pouring concrete slabs with varying degrees of success.

If you'd like to give it a try, nothing is stopping you, but it is not the method concreters have been using for hundreds of years. With this being said, it does seem to work, I just don't know how well.

I'd be weighing up the cost of hiring a mixer or getting a concrete truck in, versus the cost of replacing it if the slab fails.

Personally, I would never do it and the sentiment from construction professionals I have spoken to is that it is not going to last in the same way mixed concrete will.

I'll tag @Nailbag, @Dave-1 and @TedBear for their thoughts.

Let me know if you have any further questions.

Jacob

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/47703#Comment_47703

Afternoon @ososbg

Ive watched those videos so many times.... I dont trust them lol tho I keep watching them as it looks too easy. Anything that is too easy generally means there is a reason.

Id try it on a small area first, maybe a couple of bags big. Id then pull it up and "see" how strong that slab is. I cant imagine "wetting" dry concrete like that will give you the full strength of a mixed concrete, it wont bind right. Im lucky where I work we do destructive testing on methods of concrete and reenforcing concrete so I will be asking the guys about this one 🙂

Also will add in I was doing 10 of 20kg bags of concrete per 4 holes for supporting my deck. It was a workout and a half doing that per day lol

01 01-09-2022.jpg

My car knew it had 200kgs in the boot for sure!

02 02-09-2022.jpg

The cheapest wheelbarrow. It actually lasted until the last bag I dropped into it and I heard a large "CRACK" as the tub cracked 😲

03 02-09-2022.jpg

Made sure I was close to the holes as possible as wet concrete is heavy.

04 02-09-2022.jpg

This is why I have a problem with dry concrete, it dosnt bind the way it does when mixed properly. I suspect it would crack easily and not harden for a long period of time.

Doing it this way, I have had no issues with cracking or it moving either.

I have used the quickset concrete for posts Australian Builders 20kg Quick Set Concrete and remember not being confidant it would work as the water was eiither way to much or soaking away like crazy.

Would love to see a project put up if you try it. It would certainly be interesting. 🙂

Dave

ososbg

https://www.workshop.bunnings.com.au/discussion/comment/85883#Comment_85883

Hi @JacobZ and @Dave-1 , thank you for your reply, your last sentence sums up everything for me, as a newbie, I fully rely on expert advise like yourself to tell me what's good and what's bad. I'll do some math, but it looks like it's risky even if the math says it might be cheaper, there's a high risk for this fail in few months or a year and at this time I'll cost me even more to fix it. Plus the extra workout that Dave was talking about.

One more question for you, if i'll got with a concrete mixer or a concrete truck, is it a one man's job or it requires at least 2 people? Also let me know what the team will say about this video once they test it, keen to hear from the experts with hands on 🙂

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/108220#Comment_108220

Afternoon @ososbg

Ive never tried laying a slab of concrete yet 🙂 Purposfully I might say. Not for the reason you might expect. Having had to break up my concrete side path its given me an aversion to putting something so solid and large down as one day it will have to be broken up. Doing the mix of ten bags and pour was solid work, if you maybe staggered your slab into three sections and then did the same over three days (or six 🙂 ) I would think its possible. So a one mans job with a wheelbarrow id say is possible.

I much prefer pavers and a solid base to lay them on. I like moving things around and depending on what you want from your shed it coupd be a backup option?

Dave

JacobZ

https://www.workshop.bunnings.com.au/discussion/comment/108220#Comment_108220

Hi @ososbg,

If you got a truck and they could pour straight into the forms you may be able to manage alone, but it is still wise to have help. If you had to wheelbarrow it in from the truck, it would be a two-man job. If you hired a concrete mixer and mixed on-site, it would be a two-man job.

Once concrete stops moving, whether it is in the mixer or a truck, on a good day, you have about 30 minutes before it starts to harden. If it is hot, you'll have even less time.

Keep in mind you are looking at 1 tonne of concrete when it is dry, which is going to be closer to 1.5 tonnes when it is wet. I have moved this much concrete in a wheelbarrow before. I will absolutely never do it again.

Most concrete crews will have someone spreading and screeding the concrete as soon as it hits the ground. There's no way you can do this if you have to run back to the mixer and throw some more bags in or run to the truck to fill the wheelbarrow before running back.

Let me know if you have any further questions.

Jacob

ososbg

https://www.workshop.bunnings.com.au/discussion/comment/121383#Comment_121383

Thanks @JacobZ , make sense, problem is most of concrete people are not interested in the job as they consider it as a small job and doesn't worth it, at least this is what i've heard from a couple of guys, hence i'm looking to do it myself. Will see if someone is looking to do it or if i can get a friend to help me. Either way, thanks so much for the great help and advise you and Dave give me.

Nailbag

Hi @ososbg

100% get a "mini-mix" delivery for that sized slab. As @JacobZ It will be cheaper, more efficient and save a lot of back-breaking mixing. You will have enough to worry about floating the surface smooth and level. Don't forget your slab will also required mesh reinforcements to prevent cracking etc.

Nailbag

ososbg

https://www.workshop.bunnings.com.au/discussion/comment/47733#Comment_47733

Thanks, @Nailbag , this will be my go to option. Or as a plan B as @Dave-1 said, may consider pavers as well. I need to put a garden shed to store small garden tools (mower, etc).

Nailbag

https://www.workshop.bunnings.com.au/discussion/comment/85907#Comment_85907

Always good to have a Plan A and B in any project @ososbg 👍

Nailbag

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