Hairline cracks in concrete paving

[John HV]

Hi,

I've just spent the weekend laying our new patio with the help of a builder friend.
The slabs used were Marshalls Argent, smooth, 600 x 600. We laid a layer of compacted MOT (last autumn) and have now laid the slabs on a weak sharp sand & cement mix.

All seemed well until I went to admire the job this morning and found hairline cracks in a number of slabs (evident by the damp area bordering the crack). The cracks don't seem to have propagated where I'd expect the slabs to be weakest (in the case of cut slabs); most seem to run from near the middle of the edge, and only a few inches towards the middle.

Furthermore, only a small area of 10 or so slabs showed this damp telltale of the cracks. My thought were either a faulty few slabs, or perhaps more are cracked but only these, most recently laid, are showing because of the damper sand below them.

Obviously I'm now worrying I've hit them too hard (with the rubber mallet) when bedding them.

But items I've read on this forum have sowed the idea that the centre-edge position of the cracks could suggest they're surface cracks from drying shrinkage during manufacture.


Any thoughts? If it's a problem, what's the best cure?

Any help would be greatly appreciated.

Thanks

John

[irishpaving]

Can you get some pics up john

[jojones55]

Marshalls are great about replacing things. If you think the cracks were already there before laying, send Marshalls some photos and they will advise.

[John HV]

Thanks for replying. I'll have to wait until it rains again to get some photos.

Cheers

[mickg]

use a hose pipe or throw a bucket of water over the flags to highlight the cracks

[John HV]

Here you go. This was as the result of overnight rain. The damp marks had receeded a little by the time I got the camera. If you want a more complete view of the extent of the cracks I will use the hose pipe, but this gives you an idea of the position of them.

Notice also in the second photo the mark near the thin end of the triangular cut, but it hasn't caused it to break (yet).

[Pablo]

Those cracks are 100% manufacturers fault if it was a crack due to over hitting it always runs the full length. Those cracks have hppened during manufacture and curing. I've had that happen with Argent flags we put into a display a couple of years ago I'd reckon they'd be happy to replace them.

[John HV]

Thanks everyone. We've contacted Marshalls, and sent photos, and now wait for their reponse.