Yorkstone paving - quality grades/common defects

[moonman3]

A little bit of advice needed please.

We are in the process of having a Yorkstone patio laid. It is 600mm x 50mm by random length sawn slabs of "crossland hill" stone. The slabs have been laid on a whackered subbase, and then on a wet bed of sand and cement approx 40-50mm thick. We're waiting for the slabs to be pointed, but we've noticed that a few of the slabs have slight fissures at the edges, extending a few inchs into the slab, and which appear to run right through the full thickness of the stone.

We've raised this with the contractors and they've said that this is normal with yorkstone, and that the cracks won't get any worse.

We wondered whether anybody had ever come across this before, and can confirm a few cracks are normal. You can't see the cracks without looking specifically for them, and it was only after rain, while the slabs are drying out that we first noticed this problem. While possibly not too much of a problem in summer we are a bit worried about the cracks getting worse in winter with any water in fissures expanding.

We are also wondered whether there is any kind of quality grading for yorkstone - The stone was supplied by the contractors and seemed fine when it was delivered. We did check it but don't think we would have seen any fine hairline cracks at that stage, so we can't say whether they have been caused during the laying process or the fissures were there when the slabs were delivered. Is there a market in second quality or graded stone slabs? Are you aware of any websites that might deal with stone defects, and what is considered normal?

If you feel the stones shouldn't have slight fissures and we ask the contractors to replace them, then we are concerned that becasue the bedding layer is now dry this could disturb the other slabs - any advise on how to remove a damaged slab and relay without damaging the surrounding slabs? Do you think sealing the slabs might be an alternative to having them replaced?


Your comments would be much appreciated

regards

Moonman

[lutonlagerlout]

its a natural product moonman
its been blasted out of the ground then cut into shape it wont be 100%
i could be wrong but i think you are panicking over nothing
a picture would be helpful
cheers
LLL

[Tony McC]

Crossland Hill stone comes from just outside Huddersfield and is, generally speaking a dense, creamy buff stone with almost no colour variation. I've not seen new CH stone with "fissures", and, as LLL says, a picture would be most helpful, but I can't help wondering if these "fissures" are just a thin vein of darker material, often a coal measure.

As stone is a natural product, there is always some variation in its quality, and this variation is used in pricing when selling stone. The best quality material goes to the big commercial projects and top-end suppliers, while the medium-grade is often sold off for 'light use' such as drives and patios. The rubble ends up on Ebay where eejits who ought to know better jump at the opportunity to buy, sight unseen, "Yorkstone" at only 20 quid per square metre.

There are tests for flagstone quality, and your contractor should be able to provide details via their supplier. There are also specialists that can assess the stone and give you a quality and suitability report, but it is quite expensive (500 quid and more).

However, without seeing the stone, anything we say is mere speculation.

[moonman3]

Thanks LLL and Tony McC for your comments. I've included three pictures of some of the the cracks in the stone to see what you think-I'm certain it's not a coal measure

Your further thoughts would be appreciated

regards

Moonman

[lutonlagerlout]

hmm definitely look like crack/cracks
dont think i would have laid these myself ,especially the one over the wall,vulnerable to water ingress etc etc
LLL

[Tony McC]

That's sub-standard stone. The piece in the second piucture is guaranteed to break into two at some point in the not too distant future.

I wonder if this is 'bargain corner' stone?

[moonman3]

Thanks for your replies - certainly did not pay bargain corner prices.

It's only on a few slabs that have this problem so will get these replaced.

Going back to the original post any advice on how best to remove single flags without causing damage to the surrounding flags now the sub-base has set solid.

thanks

moonman

[lutonlagerlout]

was the stone in picture 2 supplied sawn like that?
it looks dog rough,or was that cut over the wall "in situ"??
looks like a kango hammer to break them up where they lay,might be an idea to give them a few passes with the TS 400 first to aid the breaking of them
LLL

[Rich H]

Judging by the cut they've got a TS400 but maybe they need a decent blade!

[Tony McC]

Without seeing the whole job, it's difficult to say exactly what method would best suit removal and replacement, but in most cases, a saw is used to remove ALL of the jointing material, and then the flag is lifted clear using a vacuum lift. Levering out the flag often damages adjacent paving that may be intact.