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Replacing cement fillet with lead flashing on flat roof - process

Discussion in 'Roofing and Guttering' started by MattB83, 30 Jun 2021.

  1. MattB83


    12 Aug 2018
    Thanks Received:
    United Kingdom
    Another roof post from me...

    Background (OPTIONAL READING ;)):
    I had resigned myself to having a new flat roof installed but thought I'd give patching up a final go with a tin of bitumen trowel mastic. It seems to have worked well and the majority of the roof looks to be in reasonable condition. The problem bit of the roof is on a south-facing part which I'm assuming means it gets a lot more sun than the rest - in fact this section of roof looks like it's 20 years older than the rest.

    Anyway - I think that through a mixture of patching up the cement fillet, painting joints and using bitumen trowel mastic I've removed every possible gap. My final step will be to paint the lot with blackjack all weather roof coating. This will have cost about £100 in total (£70 if I take off some felt that I didn't end up using) which I think is ok if I get a couple of years out of it. As I posted on a seperate thread - I think there is a difficulty as if I get a completely new roof I need to install additional insulation either above or below the roof which, if I've understood correctly means I will need to install some insulation in the small section of our kitchen ceiling where the flat roof covers.

    My problem:
    As many people have said before - cement fillets at the top of the upstand aren't ideal and I'd like to put in lead flashing. I'm really keen to do this myself (as on the roof is one of the few places my toddler can't follow me!) My query is:

    The whole house is in need of pointing, I'm imagining it's pointless putting nice new lead flashing in if the vertical joints above are going to let water in and down the back. The cement fillet looks like it's going to get in the way of repointing so I'm thinking of two options

    1) try to remove the fillet, repoint thoroughly and then chase in the lead flashing in the new mortar at the same level as the old fillet? My concern here is that a lot of cement has been slapped on, this appears to be a very hard mixture and, although cracking in some places, a bit of prodding suggests it's going to take a lot of removing and I'm worried I could end up damaging the felt and/or brickwork behind it.

    2) repoint as well as possible above the level of the fillet and then install the lead flashing a brick above the top of the fillet, leaving the fillet in situ. Drawbacks here appear to be that I'll need a much wider strip of lead (more expensive) and it won't look as good (although not the end of the world).

    Any thoughts much appreciated!
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