Repairing cement fillet on flat roof

Discussion in 'Roofing and Guttering' started by MattB83, 4 Jun 2021.

  1. MattB83

    MattB83

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    I'm in the process of repairing a couple of holes in a flat roof but there's a section of the cement fillet that has moved - it looks like the short vertical section of felt beneath the fillet has some give beneath it in this section - not sure if there's been some shrinkage or movement at some point.

    Anyway, deciding how best to fix it. The roof is old and I will replace when I can afford but would like to patch for the moment. A different sext it on of the fillet has had a load of bituminous paint slapped on which looks a mess but also looks well sealed. I was thinking of cementing on top of the existing cement as it looks fairly sound i.e. has pulled away from the wall in one solid piece. Is this sensible? If so, what cement mix should I be using? Elsewhere I was planning on using a lime mortar - would this be appropriate here as well? There's been some damage to the bricks - could this indicate the wrong mix used previously?

    Any thoughts appreciated.
     
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  3. oldbutnotdead

    oldbutnotdead

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    Pics would be helpful, cement fillets are always vulnerable to failing due to (usually) timber moving a bit relative to a masonry wall.
    By the sound of it this fillet is weathering a felt upstand from roof to wall? Best bet will be put a lead cover flashing on it, up to you whether you ditch the fillet or not (advantage of fillet- protects felt from wind and weather. Disadvantage- if the felt does fail the fillet will trap water & make repair difficult).
     
  4. MattB83

    MattB83

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    IMG_20210607_102044_909.jpg

    Thank you for your reply and sorry for the delay - here is a pic from above - for some reason the other uploads keep failing but I hope this is clear.

    My reluctance to put a lead cover on it is just that I'll be replacing in the near future and will plan to get lead put on then - is patching up with new mortar not a reasonable short-term solution?

    The roof is a reinforced concrete one supported by a half-brick wall above a couple of outhouses to my knowledge the felt/underlay is directly on top of the concrete so there shouldn't have been movement (!)
     
  5. MattB83

    MattB83

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    Sorry just a follow-on: if I went with lead flashing - would I put that into the brick above - or in the same row of bricks as is currently in?
     
  6. oldbutnotdead

    oldbutnotdead

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    Whether you do a short term refillet now & leave proper repair til later is up to you. You'd ideally want code 4 lead (in a sheltered location code 3 would do), the vertical bit of cover ideally wants to be 100mm so you might have to go into the course above.
     
  7. MattB83

    MattB83

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    Cheers for the information.

    Do you know if I went with the refillet plan - would I use the same mortar mix I'd use for repointing?
     
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