Concrete Problems

[algonquin]

Hi,
I have recently had a concrete hardstand poured at my property.
I am a bit concerned because the top surface seems to be spalling away. Brushing the loose chippings away doesn't seem to solve the problem. I feel that I could carry on brushing and end up with a big mound of chippings on one side and go right through the slab.
My Builder is due to return to the property and I want to know quite how to tackle him about it. I don't want him to try to baffle me with any technical nonsense.
Does anyone have any idea what is likely to have caused this? Are there any suggestions about any remedial works he can do to sort it out for me?

Many thanks.

[Atheist]

There should be no question of technical nonsense. Concrete should set hard and not crumble away. If it does, then he has messed up and should get rid of the loose stuff and replace with a proper concrete mix (not laid in frost or extremely hot weather)

[KARL]

Without a detailed description of everything from preparation onward, it is not easy to make a firm judgement although Atheist is correct. Assuming the concrete was not placed and allowed either to freeze (if there was frost) or dry out too fast, and that it was placed at least 7 days before you started brushing it, it should be so firm that you would need very substantial effort to disturb anything but the smallest dust from it. I assume that the surface was properly finished off, i.e. "closed" and smooth. One last possibility is that the concrete was past its setting points (first and second) before it was placed, or else that it was worked too much well past that stage - this would prevent it from ever setting properly.

[algonquin]

Hi,
Thank you for your answers.
I have been outside this morning and taken some photographs. I don't know whether you will be able to judge anything or comment on these but any input would be most welcome.

Many thanks.

[algonquin]

https://thumbsnap.com/GQLmeBqr

https://thumbsnap.com/eUywL4im

[douglas9401]

Hmmmm, did you buy clothespegs at the same time?

I wish you luck with your site meeting.

[The Builder]

From the photos, I think I have a fair idea.
"Proper" concrete is mostly coarse aggregate (usually 18mm chippings)
Whatever they've given you, it appears to have far too many "fines" in it. In fact, it looks more like quarry dust.
Coarse sand is best for concrete, i.e. less fines.

Fine stuff is said to "eat" the cement in the mix. It makes it powdery, friable (easily crumbled), and structurally pretty useless.

A decent mix will happily take light traffic the next morning. I wish you the best of luck. It's an awful position to be put in.

[algonquin]

Thank you for your answer - The Builder.

Is there any sort of remedy for this horror, or would it be best taken up and started again?

[The Builder]

If there was no problem with height, it could certainly be concreted over.
But, to be practicable, it really should be replaced.

I suppose pouring gallons of waterproof/exterior PVA over it would go some way to re-constituting it, but I couldn't guarantee how long it would last.
In these situations, digging it up and starting again is the only way.

[algonquin]

Again, thank you. I am much obliged.

Please have a Best Answer.

[algonquin]

One last thing, if my Builder offered to sort it out by laying paving flags on top, would that work?

Providing we have a level area to sit out on and enjoy, it wouldn't matter whether it was concrete or flags.

[The Builder]

Yes, that would be fine. It would be a perfectly good base.

I don't want to make things more complicated, but slabs are usually laid on a 50mm (2") base. That, plus the 1.5" thickness of the slabs would raise things up a little.

Some height could be saved by bedding them on a normal sand & cement mortar base (0.5" or thereabouts.)
It would save 1.5". I don't think I would go for that though, since it doesn't leave any wiggle-room for falls (slopes to run the water off.)