Haunching my chimney - plan of attack ok?

kingandy2nd · 12 Apr 2021

Hi All,

My chimney is in a bad way.

I'm just about to do the roof on this side of the house, which will included replacing all the lead...but before that I want to sort the chimney out. The house will be getting rendered including the chimney, but I think I need to remove/replace the blown bricks and the haunching.

I was going to remove the entire top layer of brick and replace with blue engineering bricks and 4:1 mix - sorry if this is a stupid question, but do the bricks go all the way across under the haunching? If not, how else is the central part of the haunching supported in place?

Repoint the rest of bricks with 5:1 mix.

Regarding the haunching, I see that 3:1 mix is recommended. Could I add some tone to that to make it grey?

Finally so you think the chimney pot will be salvageable once I start removing the existing haunching, or should I just order a new one and be prepared to replace?

Thanks in advance
Andy

ps - I'm going to remove all the old aerials, metalwork, etc

^woody^ · 12 Apr 2021

Rendering chimneys should be avoided as they can become a regular problem when the render starts to detatch very soon and paint peels. If you are dead set in rendering, use a sulphate resisting cement and replace any blown bricks, and consider a render that is low maintenance and does not need painting - even if different to the rest of the house. If bricks are loose, render will crack and pointing won't hold them together

Two course of blues should be laid to avoid frost problems - with a good oversail from the render face, not just the brick face

Sharp sand in the flaunching along with building sand is just as important as cement - 2:1:1. Why would you want to dye it grey? Flaunching dries grey and the pigeons wont mind,

That looks like a 3-flue stack so there will be bricks (whiffs) across the stack between the flues. The pot should be reusable if its in good condition now.

kingandy2nd · 12 Apr 2021

Thanks Woody. Yeah, I definitely want the chimney rendered otherwise it's going to look strange as the rest of the house will be white. I'm have silicone render (Baumit) done.

The chimney is in a 70s house that has never had anything other than a single gas fire downstairs so strange they've made space for 3 flues.

Was aiming for a 25-30mm oversail.

kingandy2nd · 12 Apr 2021

Bit of yanking by hand has led to this...definitely worth sorting before it fell down.

Fair play to Mother Nature and a blackberry plant growing inside the chimney pot

noseall · 13 Apr 2021

Drop some concrete slabs on top with oversail.

catlad · 13 Apr 2021

Knock it down! its useless.

kingandy2nd · 13 Apr 2021

Thanks guys, but I do have a gas fire in the living room with a flue that is connected to the one chimney pot, so I think I need to re-build as was.

^woody^ · 13 Apr 2021

If you are rebuilding definitely don't render

kingandy2nd · 13 Apr 2021

I'm only going to rebuild the top part Woody.

You really are against rendering chimneys... it can't be that bad can it? It's never been a real chimney with smoke coming out of it...

23vc · 13 Apr 2021

I did some rendering recently over various bricks including engineers, and did a slurry coat of neat SBR and cement, it may help, it’s pretty rock solid when it goes off and I can’t see much unsticking it. Then scratch coat while it’s still tacky. That’s for sand and cement render tho, may not be suitable for the silicone/mono stuff.

catlad · 13 Apr 2021

That chimney is not suitable long term for that appliance, thousands of gas fires with the appropriate terminal without a chimney since the late 70,s

kingandy2nd · 14 Apr 2021

catlad said:
That chimney is not suitable long term for that appliance, thousands of gas fires with the appropriate terminal without a chimney since the late 70,s

Hi Catlad,

Thanks for the comment, but I’m not sure I understand why it’s not suitable long term?

The house was built in the late 70s with a gas fire and a flue up the chimney.

The gas fire we have now, modern living flame jobby, that requires a flue... so I don’t really follow.

^woody^ · 14 Apr 2021

kingandy2nd said:
it can't be that bad can it?

Yes. Stacks are really exposed which is bad enough, but add to that just a slight quality issue in the work (which is often unavoidable) and the render detaches in no time - and then you end up with a maintenance problem that's difficult to deal with.

catlad · 14 Apr 2021

What I am saying is you don't need all that masonry in this day and age to vent a gas fire which you probably use half a dozen times a year!
Its in a bad position at the bottom of your roof and its a lot wider than is needed, some vents even come out of the side wall for fires these days.

kingandy2nd · 15 Apr 2021

Thanks @^woody^ and @catlad that all makes sense.

Wouldn't working on the flue require a gas safe person to make the adjustments? The problem I've got is that I'm on the clock now for the renderers who are coming next month. Probably in the ideal world I'd remove the chimney and do something else, but I don't have the luxury of time for doing that now as I've got to re-roof half the house in the next few weeks.

All I can do is replace the removed bricks, repoint the whole chimney and cross my fingers regarding the render. I'm getting the pros to do the render with the meshes undercoat and silicone top coat.

I've got custom lead back gutter and front apron coming from leadworx for the current size, which should help with ensuring it stays water tight.

Now I understand the issued, it a different situation I would tackle as advised, but I don't think I've got the time to do it as suggested.

The only positive I guess that I do have is that the chimney is completely separate from the rest of the house walls due to the fascias/soffits so there will be a break in the render from the rest of the house. If it does start to fall off at some point in the future, then I could take more drastic action with the chimney when time allows.

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Haunching my chimney - plan of attack ok?

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