Cavity trays and flashing on a flat roof abutment

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29 Jan 2012
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Dorset
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United Kingdom
I have a flat roof that abuts a vertical wall.

I installed 'refurbishment' type cavity trays which are the type with no lead attached, just a clip that keeps the spacing while the motar goes off.

The clips are then removed and the lead flashing goes in under the lip of the tray.

So my question is, what's the best way to seal the joint between the tray and the lead? Manthorpe (the tray manufacturer) doesn't say exactly what to do. I presume I could get a thin bead of leadmate under the tray and push the lead into it?

To get the lead in under the tray, it needs to go 2 inches into the wall, which is further than normal?

Also, there is a weep in each tray, but using leadmate to fill in the joint afterwards makes a water tight seal, basically keeping the water pooled in the tray until it finds the weep. would a motar joint between the lead and the brick not be better as it will allow moisture to escape quicker?
 
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