Concrete mix; have I made a big mistake??

[martinlarsson72]

Spent the whole weekend making a slab for a dog run, 3.5 x 2.5 m. As a happy amateur (implying sloppy) as one can sometimes be, a couple of bags of cement were procured, which were then mixed in the wheelbarrow with crushed stone (probably 0-4) and leftover crushed 8-16 that I had on the driveway. I now have a feeling that the finished product isn't very high-quality concrete

I laid about a 5-6 cm thick layer (about half a cubic meter in total), and for all of this, only 2 bags of cement were used Didn't really think much about it when I was working on it, but I have a feeling that it probably should have taken 5-6 bags??

My question is, will the slab be good for anything at all, and is there anything I can do to avoid redoing everything? It's, as mentioned, for the dog run, and the only reason I laid concrete there is so the dogs can't dig their way out, so that's the only thing it needs to withstand. The concrete will only be loaded with the weight of the dogs (the fence segments will be attached to wood frames lying around).

Grateful for feedback!

 

[saturnus]

It depends on what type of bags you're talking about . But if it's the usual 25 kg ones, you should have chosen 6-8 pieces. What's important is that the "bed" = under the cement, is properly packed, if it's now supposed to hold up for the dog to walk on. But I would have chosen to redo it before too much debris gets on the slab. Form a new edge and pour a new slab on top. Try to include some reinforcement as well.

 

[martinlarsson72]

It depends on what kind of bags you are talking about. But if it's the usual 25 kg ones, you should have chosen 6-8 pieces. What's important is that the "bed" = under the cement, is properly packed, if it is supposed to hold for the dog to walk on. But I would have chosen to redo it before too much debris gets on the slab. Form a new edge, and cast a new slab on top. Try to include some reinforcement as well.

Ok. A bit disappointing news, but not entirely unexpected Admittedly, the soil underneath is very well packed, plus I laid down geotextile too (since I initially planned to buy some pre-made slabs), but I understand the point. As it is now, there are 4-5 cm up to the top of the beams, would it make any sense for me to try casting another layer on top of the existing one, or will there be issues with layering and cracks??

 

[saturnus]

It's fine to cast on top of the previous one, but don't go up there with muddy boots. However, if you have soil under the slab! you should probably increase the thickness of the new slab to about 80mm, otherwise, it will likely crack as well. It's a bit stiff to mix in the wheelbarrow, but on the other hand, you can skip the usual jogging round. 1 shovel of cement to 3 shovels of gravel, and mix it dry first, i.e., add the water last. And don't make the mixture too loose = too much water. If you have more 8-16, you can mix this in last; you don't need to keep turning the mixture with the stone in it, just a few turns are enough to mix the stone.

You might consider casting pieces of fully threaded rod (M12) into the new slab, which you can then bolt to support whatever you need for your grills. Better to have these ready in the slab than to drill and plug/expand afterward, which can crack the slab.

Remember: all material mixed into the cement must be clean, i.e., no soil in the mix.

 

[martinlarsson72]

Ok. Probably short on time to redo it this summer What is likely to happen if I leave the current mass there? Will it crumble into sand and stone if you walk on it??

 

[saturnus]

Yes, it will, but maybe it's better that way, so you can start over. Then replace the soil underneath with 8-16, otherwise the slab will remain damp.

 

[Mats]

If you buy Cementa bags, the recipe is printed on the back. Therefore, I always make sure to have a Cementa bag lying around. Otherwise, I think it doesn't matter whose cement you use, but the "cookbook" is a bonus.

 

[Watchmen]

I can only add that embras and cementas cement, which 95% of companies use, comes from the same places. Due to a cement shortage

 

[martinlarsson72]

Let's see if I can rent a concrete mixer, so maybe I'll have a chance to get the proportions a little better next time I try it. It feels a bit easier to mix larger quantities all at once than to scoop everything in gradually in a wheelbarrow

I also have some chicken wire lying around that can serve as reinforcement, so with a bit of luck it will be better next time

 

[mycke_nu]

uh.., the reinforcement should provide tensile strength, so spend a couple of kronor on real reinforcing bars and you won't have to redo the job yet another time.

 

[jon_h]

Chicken wire does not work at all as reinforcement, you might as well do without it.

Edit: Mycke_nu got there first.

 

[Mats]

at least take a real armeringsmatta

 

[LLLVäxjö]

Buy a cheap personal scale + bucket and calibrate it with a known weight that is close to what you will weigh (the materials), to achieve more consistent concrete batches.

 

[Mats]

A regular 10-liter bucket works quite well as a measure. 2 buckets 8-16. two heaping 0-8 and half a sack of cement plus a decent splash of water for example

 

[Tigersågen]

If you have plenty of money and want to avoid the hassle of getting the right mix of cement and gravel, one option is to buy pre-mixed coarse concrete in a bag. Then it's just a matter of adding the right amount of water. It will be at least 3 - 4 times more expensive but saves some work from having to start over .

Regards/Tigersågen