Flashing

[Frank]

I have to replace the seal between my lean-to greenhouse and the gable end wall of my house. The original used roofing felt which is now brittle and useless. I know nothing about flashing(!) The DIY wiki is silent on the subject. Help! The sheds sell rolls of flashing which seems to be some sort of grey plastic with a sticky backing - I want to know how it is used. One thing the DIY wiki pointed me to was a series of building manuals written by one Robin Barry. They sound definitive - but which of the 5 volumes might help me?

Incidentally, the wall to be sealed to is harled i.e. nothing smooth.

TIA Frank

[Dave Plowman (News)]

If you want something to last, use lead. It's very easy to work with. But will need to be cut into the wall by about an inch or so. Normally by raking out the pointing between brick courses. I realise this is a problem with a rough cast wall. So easiest way would be to cut a slot with an angle grinder.

[Frank]

I have some lead from a demolition on a neighbours house. How deep would the slot in the wall need to be and how is the lead fixed into the slot? Frank

[NT]

Lead: lasts a lifetime. thievable Roofing felt: only lasts so long. Lasts better if fully supported, eg on top of cement/sand cement sand, weak mix: works if no movement, but movement tends to happen. Not a great option, but its used Bitumen: not very tolerant of movement Gloopy roof sealants: usually bitumen

NT

[chris French]

About an inch deep maybe? The lead is fixed into the slot with little wedges made of folded over lead sheet. Then repointed, or a sealant used in the gap.

Wickes do a pretty good leaflet on leadwork:

[Phil Addison]

If that is the start of a wiki... Sylglas: An aluminium faced bitumen(?) tape. Very good to seal glass to aluminium greenhouse frame. Best done in mild weather when its pliable - I had to do our greenhouse in 2 degC winter when a roof pane got broken, and needed the heat-gun to soften it. (not sure if it will bond to roughcast, proper flashing best for that as above).

Phil

[John Rumm]

About an inch deep (not that critical). Cut a thin strip of lead (about half inch wide, and then chop into 2 - 3" lengths. Fold these over a couple of times to make a thicker "blob". Once the lead is in its slot, tap the blobs into the gap with a bolster chisel etc to wedge the lead in place. Then dress it down over whatever you are flashing, and seal the gap with flashing sealant or re-point it.

If doing long lengths, restrict any single piece of flashing to about 6' maximum, then start another bit - overlapping the previous bit by 4 -

6". This prevents it all wrinkling up or fracturing with thermal expansion. (if doing he overlap on a sloped section, then make sure you get the higher bit on top!)