Roof Flashing

[Rob Bashford]

My ancient house has a roof of clay roman canal tiles. These but up to the wall of next door's property, which is higher than mine. The joint is made with a mortar flashing, which has reached its sell by date and is cracking in places allowing water to pass behind it.

I need to remake this joint. Is there a better way than mortar? Is there a bitumen based product that can be trowelled on to form the flashing fillet.

A metal flashing is not possible because the wall is rendered and not mine to cut in to. A few years ago I used flash band to temporarily cover parts of the flashing. This has been successful but does not look good or last very long.

Advice would be welcome.

[Dave Plowman (News)]

Surely it's a party wall? Even if not it would be in your neighbour's interest to have a proper repair done - water running down a wall is never good news. Rendering should be easy to repair after cutting a channel for the flashing.

[dg]

A traditional mortar fillet has served well on the majority of houses built since the middle ages. There is no reason why any new fillet should not last your lifetime.

I recently returned to a job we did 18 years ago to replace some mouldy twinwall sheets to a carport roof. The flashband we used around the roof was undamaged and still doing its job.

You could try a flexible fibreglass based sealer ( "Acropol' or similar), but this will need a sound base to paint on to.

dg

[Huge]

Yes. I have repaired some valley flashing on my roof using trowel on bitumen "emergency" roof repair stuff. The alternative being to strip off two rows of tiles in order to replace the flashing. I put "emergency" in quotes because although that's what it's called, it's been up there for about 4 or 5 years now. You do need to use it in warm weather ...

[Dave Plowman (News)]

But surely in conjunction with soakers?

Might depend on the type of mortar used?