Help with coping stone things

[Mw Roofline]

I don't normally deal with this but a good friend has asked me to have a quick look at one of his coping stones (I don't know the technical term for them)

The front of house pic shows the general layout of them and the other pics show that the bottom one has slipped down about 3 inches.
He is worried it will slide off?

My question is, do you think there are some raised ridges/stoppers on the underside of the stone that stops it sliding off? I think water has got in and eroded the brick the stone sits on and has caused it to slide down.

Or is the stone flat underneath? So no angle iron or anything, just compo holds it in place?

 

[Mw Roofline]

View media item 95254 View media item 95255 View media item 95256

 

[ree]

Mw Roofline,

The parapet coping stones have dropped by about 25mm on the LH verge parapet. The coping stones are meant to project by about 50mm.

At the bottom the movement has cracked off a patch of render.
At the upper coping stone some render has also been pulled away.

The step cover flashing should not be rendered over but i dont think that its a contributory factor.

I would date the building to be about 100yrs old. But gravity has caught up with it. Tiny hairline cracks probably allowed moisture in, and freeze and thaw over the years has gradually opened the cracks. And, as you suggest, penetrating moisture has disturbed & loosened the S&C bedding below the stones.

Whats to be done:

Best practice would be to scaff up, and remove all the coping stones up to to the upper "cracked" joint or even higher.
Remove all the inner render and check out the flashings.
Renew any loose or perished brickwork thats revealed.
Re - render, with the cover flashings & soakers fixed appropriately.
Check for leaks in the interior "attic" below.

Two SS "hip irons" could be fixed the bottom of the run.
Re-bed the stones on 4:1:1 mix of S:L:C. Use 10mm joins. Butter the stones.

The alternative:
Would be to disc out the joins and point up.
Patch the render.
Fix some kind of angle bracket with a say 300mm leg bolted to the brickwork below the bottom stone - this will prevent any further sliding down.

FWIW: perhaps inspect the whole roof and parapets and render for other signs of disturbance eg. the RH side of the bay render seems to have shelled.

 

[^woody^]

These tend to be flat bottomed with no nib to the wall below.

Sometimes, a bolt or two can be drilled through the end stone and this will provide the necessary key to stop it sliding further. But it all depends on the condition of the wall below, and it does not help with that big open joint

If the joint has been open for a long time there could be further deterioration of the wall and render below - non of which will be getting any better. That much displacement can only mean that it's just their weight and friction holding them now, as the bed joint would be cracked.

 

[Mw Roofline]

Thanks Ree/Woody

Woody, job for you? (Birmingham)

 

[^woody^]

Thanks, but I'd have to decline.

I only like the easy jobs for my foreigners