Chimney top

Discussion in 'Builders' Talk' started by rogerk101, Oct 15, 2021.

  1. rogerk101

    rogerk101 Screwfix Select

    This is a bit of an unusual one, so beware ...

    I have an unused brick chimney with a chimney top made out of three layers of roofing tiles all laid flat and bonded together with mortar. There are two unused stubby chimney pots protruding from the top surface of the chimney top, each of which has been capped off with a large flat roofing tile. It's a real mess, but so high up that no one pays it any attention. It is a constant maintenance chore to climb right up there to refresh the bitumen sealant that I use to keep the whole thing water tight, as the bitumen seems to break down every couple of years, exposing some cracks and allowing microleaks, which during subzero conditions freeze and then widen the cracks, and it's a downward spiral from there.

    I'm considering removing the whole mess to expose the topmost layer of bricks and then lay a single weatherproof surface on top of the whole lot. It's an awkward size that I need (113cm x 67cm), so just too big for 1200 x 600 slab of something like a tile backerboard (eg. Hardibacker of Aquapanel). I have considered all sorts of alternatives, like a granite/marble kitchen worktop which can usually be picked up second hand on eBay for pocket change, but they too are usually limited to 60.5 cm or thereabouts.

    My question/challenge to the group is to propose good ideas on how to achieve a nice simple solution to provide a weatherproof topping to a chimney that is 113cm x 67cm (including about a 4 cm on all four sides overhang).
  2. Jiml86

    Jiml86 Screwfix Select

    Would chimney caps not work over the two chimney pots?
  3. rogerk101

    rogerk101 Screwfix Select

    Yes, they do, and they aren't where the problem lies. The problem is that the entire chimney top is completely original, so 70 years old, made up of roof tiles and crumbling mortar, and filled with hairline cracks.
    It's probably been like that since it was built, but in the old days, there would have been fires in the fireplaces and the huge draughts that would have been passing through the chimney would have kept it aired and dry(ish).
    I bought the house 15 years ago, and tried to address the hairline cracks with bitumen weatherseal, but that stuff needs to be reapplied every couple of years, and I'm looking for a way of rebuilding the chimney top so I never have to maintain it again. I'm 64, so if I'm lucky I will only be able to climb on the roof to do this stuff for another 10 years or so. I would love to be able to say that it's capped off good and proper and won't ever need sealing or attending again.
  4. BillyT

    BillyT Member

    Hardibacker comes in 1200mm x 800mm sheets and can be easily cut to size. Not sure it's suitable for external use though.
  5. Jiml86

    Jiml86 Screwfix Select

    Ah yes I see, interesting issue, I wonder what's beneath the tiles and mortar if you strip them back to roof level? Would it be an option to then build up a couple of rows of brick then cap with a concrete cap stone
  6. JOMEL

    JOMEL Active Member

    Well you you maybe in for a suprise.
    I am only 88 and her indoors has chained my ladders up.
    And hid the key.

    Ah well

    Johnny M
    rogerk101 likes this.
  7. Jord86

    Jord86 Screwfix Select

    A piece of slate from a nearby or reachable quarry.
    rogerk101 likes this.
  8. Abrickie

    Abrickie Screwfix Select

    Take it down ? No maintenance and no leaks ;)
  9. rogerk101

    rogerk101 Screwfix Select

    Not sure what you mean, but taking the whole chimney down isn't an option. It's an integral part of the gable end of the house and would be FAR too disruptive to even contemplate.
  10. rogerk101

    rogerk101 Screwfix Select

    I have considered that, and am in fact looking on Gumtree and eBay for all sorts of slabs of weatherproof whatever ... slate, paving slab, kitchen worktop, concrete board, tile backerboard, Knauf exterior Aquapanel, Hardibacker, etc.

    I'll let you all know what I eventually use.
  11. stevie22

    stevie22 Screwfix Select

    Would casting a cap in place be viable? It sounds as though getting a big lump of slab up high might be a challenge.
  12. rogerk101

    rogerk101 Screwfix Select

    That's certainly something I've considered. It'd be quite tricky attaching the necessary shuttering, but perhaps a few good clamps would work. Thanks for your suggestion, as it proves to me I'm not completely daft!
  13. stevie22

    stevie22 Screwfix Select

    Watch a couple of Fred Dibnah videos: anything is possible!!
  14. rogerk101

    rogerk101 Screwfix Select

    As an update ...
    I found (and won for £60) an eBay auction for a single sheet of brand new code 5 lead 1.2m x 1.5m. This is is easily big enough for me to cover the entire chimney top and still have enough of an overhang to create a drip edge. This will will stop the dreaded capillary action that I believe is the primary cause of the water damage I'm seeing in the room right near the chimney.
    I'll be collecting it on Friday, and weather permitting, installing it on the weekend. It's going to be a beast to lug 3 storeys up a ladder, but it should do the trick.
    I'll report back on progress, but it will be a good few weeks (maybe months) before I'm able to say for certain that it's cured!
    Many thanks for all the advice offered above.
    Starslikedust likes this.
  15. stevie22

    stevie22 Screwfix Select

    4 Wheatabix day I reckon Roger. Fingers crossed!

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