The Brew Cabin

Owing to problems with getting one inch york paving stones, I was persuaded that 3/4" would be ok for a lightly used patio. I don't know whether this is the cause, but my builder is having some problems getting them to stay put, however. They are laid on a solid, steel-reinforced concrete base (I hope that's the correct term) and 'normal' mortar for the bedding. They seem to be coming loose after a couple of days and rocking in their place settings. My builder thinks it's because they are a non-flat surface, but I assume that is bollocks. Any advice would be greatly appreciated.

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What type of 'mortar' is being used to bed these flags? Is it a wet mix or a semi-dry? Where did you obtain the flags? Whereabouts in the UK are you? Are the joints pointed or left open?

Sorry about the username cock-up. I've reregistered.
The Mortar is wet mix. The flags were obtained from BRS Yorkstone, North Yorkshire. I believe the guy runs about 3 or 4 Quarries. It is all new & machine cut. I am in Wimbledon, SW London. The joints will be pointed but are open at the mo. Hope this helps.

Jason

Thanks for sorting out the 'name'. :)

These flags aren't de-laminating, are they? They are coming loose from, the bedding which is a wet mix mortar with adequate cement (say, 6:1 or thereabouts) - is that right?

If so, it suggests the laying method is wrong in some way. Is the contractor tapping them down properly so they bed into the mortar rather than just sit on top of it? Is the bedding thick enough - ideally it should be 35-50mm - and what is it laid on top of? A sub-base or bare earth?

I presume delaminating mean flaking off. If so, they don't appear to be losing anything from the surface. The mortar is standard wet mix with the correct ratio. They are laid on a solid concrete base.

The contractor thinks that because the flags are bowed unevenly (eg one side curves up, the other down), if you step on them it lifts the other side causing it to become detached which seems wrong to me. He is tapping them into the mortar and all the other work he's done has been excellent. Its a bit of a mystery.

Jason

Yes, delaminating can be thought of as 'flaking'. The separate layers (laminae) that make up a sedimentary rock, such as sandstone, start to lift and come away from the rest of the rock. Often a sign of a poorly cemented rock type or excessive frost damage.

Anyway, back toi the flags in question - even if they are bowed, Jason, it shouldn't make them 'rock' when you walk on them. The bedding mortar should take up any difference in the profile of the flags.

Have they been trafficked (by people) in the first 24 hours or so after laying? This can loosen them from a full bed and cause them to rock. Other than that, I can't think of any other reason why they should behave like this.