Coping stone catastrophe . . . . .

[TheSalad]

Hi folks - due to leaks we had coping stones on a parapet wall above our garage replaced earlier this year. All seemed in order until the first frost. Now we have leaking more than before.

Paving slabs with a drip groove cut in to them has been used. I don't think the person we hired has done anything like a good job. I'm no expert but from what I see the mortar has cracked, the bridging gaps between stones are poor and the DPC is not bedded in.

I'd be grateful for your observations and advice. I will be hiring in someone else but I need to ensure they do everything right this time.

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• TheSalad
• 30 Dec 2017

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• TheSalad
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• TheSalad
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• TheSalad
• 30 Dec 2017

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• TheSalad
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• TheSalad
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• TheSalad
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[John D v2.0]

Needh more overhang to protect the wall. Also the main issue is you need proper sealant between them, mortar is useless in that location.

 

[bobasd]

i'm thinking the DPC is under the capping stones. its not doing much in that position but destablising the lightwieght capping stones.
if you bring it down lower youd need to step it along the parapet to follow the roof falls.
but you would then have problems at the shallow end of the parapet.
whatever you do with the dpc an flashing it might be better to have a rebuild because the detailing looks to be wrong and the pointing is no use, pure DIY stuff.

the flat shelf after the angle fillet is what? why is it there. the GRP upstand where it meets the leadcover flashing itcould be sucking water up. lift the lead an photo whats there.



is the end, the gap near the house with lots of flashing doing its job?

ther are other methods of dealin with parapets. but see what the new man wants to do first.

 

[John D v2.0]

Ah didn't see all the photos, slow 3g
A garage isn't a habitable space so it should be able to handle getting damp. Single skin walls are not weather tight so the water can run down to the lintel and then it's either going to go in or out.
I think you're on to a bit a la m damage limitation of you want to stop that water.
Normal walls in houses would have a cavity tray to collect all the water soaking through that leaf and direct it outside. Then the inner leaf would stay dry.
Other suggestions on top of the above would be to render all the fair faced brickwork around the lintel on both sides, and try to make the water drain somewhere better when it comes through to inside. That lead flashing should rise all the way up to the stones, or there should be a vertical dpc or some other way to protect the inner side of the wall from penetrating damp.

 

[TheSalad]

Needh more overhang to protect the wall. Also the main issue is you need proper sealant between them, mortar is useless in that location.

Thankyou. What is the recommended overhang? And what would 'proper sealant' be?

 

[bobasd]

The walland parapet is a two brick nine inch solid wall.
the overhang is ok but up from 32mm like yours to 50mm.
the joins are usualy tighter than yours but nothing wrong with mortar..
you have two different mixes of mortar

 

[John D v2.0]

I'd say overhang 50mm would be best.
The s had the be suitable for external and flexible, something from here would be fine
https://www.sealantsonline.co.uk/Products/Exterior-mastic-sealants

 

[^woody^]

Overhang not wide enough.

Drip groove too narrow and too near the edge

Slabs laid too flat.

Mortar poor and not pointed properly.

Lead flashing not deep enough to prevent capillarity and splashing getting behind it. The whole of the back face should be flashed.

If the parapet is otherwise sound, instead of rebuilding, you could spend £70 or so on some silane clear waterproofing and brush that on the copings and wall