Scaffolding on the road Woes for reroofing

[andrew gayton]

Wow. Those pots are m a s s i v e ................... The wind loading on that sort of surface area would certainly be enough to loosen them over time - bearing in mind that the base of the pots only rest on a minimal surface area [of stack or slate/metal packing] before being flaunched up (and look at the volume of flaunching that has been used [the builder knew that there would be trouble ahead :wink: ]) - so anything you can do to minimise that would only be for the good. I assume that the pots are that tall because of down draught / draw problems? is there scope to raise the stack brickwork to help reduce the size of the pots, or do you wish to retain the existing pots?

Without going into massive detail, there is an act from 1996 (although it might be 2006) which allows you as a property owner the right to maintain your property. I think that you might well have been able to serve a notice of sorts on the highways dept. basically informing them of what you intended to do before actually doing the works - this *might* question the whole issue of permission being required from them - I might have to check that in more detail.

Also, if dangerous structures issues couldnt be made applicable by B.C, then I am sure that the H.S.E would be interested..............

it must have been completely frustrating getting this sorted out.

 

[88v8]

Where's Fred Dibnah when you need him... I might be inclined to try tying those pots together with a steel wire, on a better-than-nothing basis ... or
perhaps take the view that they've been there a good few years so don't worry... but they sure are tall.

Alternatively, another couple of courses of flare on the stack to make the head wider... then the flaunching would have more leverage, if you follow me.

Ivor

 

[andrew gayton]

I wouldnt tie them together.................. more likely to fail under wind loading as a unified mass.

 

[agbagb]

It was frustrating, but I think they saw sense in the end. Ultimately they would have argued why the skinny scaffold would be unreasonable. The test of being reasonable goes some way to pushing through the varius codes of practice written for "normal" situations.

Yes BIG Pots. The top 5 or 6 courses of brick will be rebuilt as it is spreading. Flexible linners going down and the pots refitted. I'll ask the question about long term stability but it looks like its spreading of the brickwork that caused the lean. Maybe the top plates for the linners could be fixed together in some way. The other half won't let me work on the roof so I'm relying on the builder for all this.

 

[andrew gayton]

the initial lean then the subsequent split will have been caused by both wind loading, thermal distortion (one side being warmer than the other) and thermal disparity if one flue has been used more than the other. Combine all of that with 4'' thick brick, unbonded b.o.e whiff wall, sulphate attack and cement repointing and its no wonder that stacks lead a hard life. Use bed joint reinforcement and if using cement (here I would) use sulphate resisting cement. This might shock some, but a waterproofing admix in the flaunching will put a decent 'hat' on the stack.

Yes. A conservation professional has just advocated the use of cement and an admix.

 

[stuart45]

A lot of bricklayers make the mistake of using the flaunching only to secure the pots.
25% of the pot should be built into the brickwork, especially with tall ones.

 

[agbagb]

Thanks Andrew, I'll put that to builder. The bed joint reinforcement makes perfect sense. But just to clarify:
1. Should the 5 or 6 courses that will have to be rebuilt be with OPC or just the flaunching? I was originally thinking of NHL5.
2. With stainles flexible liners in do I still need sulphate resistant cement?

Thanks Stuart, That makes sense as well although 25%, in this case, is a lot of pot. Maybe if I drop the liner plate in say 3 courses down (hence the bottom of the pot also). The top courses with the bed joint reinforcement and then the gap between the brick and pot filled with a weak concrete. Although any future flue replacement would be a job and half.

 

[andrew gayton]

A lot of bricklayers make the mistake of using the flaunching only to secure the pots.
25% of the pot should be built into the brickwork, especially with tall ones.

I have never seen this done. Typical 'flue v pot' base dimension would not allow this; I can only assume that you are referring to stone as opposed to brick stacks.

Every chimney I have seen has the pot sat on either metal or slate packing which is then flaunched over with broken tile and mortar.

This is quite a vulnerable detail, hence my advice to use waterproofing admix for this mortar (and this mortar only). The flaunching should be built up in the centre to allow a good run off.

 

[andrew gayton]

Thanks Andrew, I'll put that to builder. The bed joint reinforcement makes perfect sense. But just to clarify:
1. Should the 5 or 6 courses that will have to be rebuilt be with OPC or just the flaunching? I was originally thinking of NHL5.
2. With stainles flexible liners in do I still need sulphate resistant cement?

Thanks Stuart, That makes sense as well although 25%, in this case, is a lot of pot. Maybe if I drop the liner plate in say 3 courses down (hence the bottom of the pot also). The top courses with the bed joint reinforcement and then the gap between the brick and pot filled with a weak concrete. Although any future flue replacement would be a job and half.

If you are proposing to use NHL5 you might as well be using opc and sand. I would use a 1:2:9 - 1 part sulphate resisting cement (the best cement to use in this situation, lined or not, if reusing the bricks), 2 parts non hydraulic lime and 9 parts sharp sand. same mix for the brickwork and flaunching

The whole issue of flue lining is almost a stand alone topic. Historically, flues were warmed and vented, now they are being lined and unvented - and internal sulphate staining is on the increase; one problem solved, another one created (and I am sure that stack brickwork will decay ata faster rate also)

Stick with flaunching the pots how they are at present - although I would come back to building up the brickwork courses and using shorter pots.

Dont do the concrete thing.

 

[stuart45]

A lot of bricklayers make the mistake of using the flaunching only to secure the pots.
25% of the pot should be built into the brickwork, especially with tall ones.

I have never seen this done. Typical 'flue v pot' base dimension would not allow this; I can only assume that you are referring to stone as opposed to brick stacks.


.

The ones you have seen are quite common but wrong.
I was taught this method at Tech as an apprentice bricklayer in the 60's and have normally built stacks like this.
On chimneys without a liner the pot should just about sit on some of the brickwork with the aid of slate in the corners. The brickwork is then oversailed for a few courses and then brought back in as the taper of the pot allows for this.
On modern the pot sits on the liner to makes things easier.
I will try and find a few photos from old textbooks later on.

 

[andrew gayton]

Thank you for the clarification.

The 'newest' chimney I have seen in pieces is late 19th c where pots have not been 'in built'.

 

[Lime]

From the picture the long pots have been used to raise the flue height in relation to surrounding buildings to overcome downdraughts.
I'd favour increasing the height of the stack.
I have never seen pots "in built" on older property either.
However if the stack is raised, in built pots may be a good idea considering their length will allow it without altering the character too much.
(Most people never see their own chimney pots but spend a large proportion of their time looking at other peoples' out of their windows. )

I have observed that chimney pots on older property are ALWAYS bigger than expected.
Most people do not appreciate the foreshortening caused by the height of the pot, the fact that pots are often on long stacks (longer than they look) and the pots have a portion of their length embedded in the flaunching.

 

[stuart45]

A few pics to explain it better. I would say that the majority of bricklayers I've worked with don't know the correct method.

 

[andrew gayton]

Stuart - thank you for posting those. Mckay's by any chance?

 

[agbagb]

Thanks for all the input. I had a call from the builder last night, he's taken the stack down 7 courses and rebuilding today. (1:3 NHL3.5 to sharp). Linners going down and pots going back up on Friday. I mentioned about pot stability, he says he will faunch about 6" and is confident they'll be OK (done loads of pots this size in the past). Although I think most will have been with OPC.
I'll be on site on Friday so will have a chance to influence things. I might be able to get some galvanised steel reinforcement in the flauncing, a square ring around both pots.

It's frustrating not having total control.

 

[Flyfisher]

Interesting drawings and easy to see how they would result in a very robust construction.

We have five chimneys and I've had the tops of three of them rebuilt and the pots re-fixed - none of them were constructed in the way shown in those diagrams. Also, I can't recall ever seeing chimneys with so little of the pot protruding, so can we conclude that type of construction is fairly rare?

 

[DJH]

It's common enough to see the FF but, in reality how many of us go around looking at chimneys? I'm notorious for looking at leadwork as I'm driving around, well glancing I should say and I've even missed the odd mini skirt now and then. :shock:

Long pots were sometimes retro fitted to solve downdraft problems say from nearby trees that have long since gone and the pots have stayed put.

Doug

 

[stuart45]

Stuart - thank you for posting those. Mckay's by any chance?

No, the 4 flue one is from Practical building and decorating Published 1957, and the other from Brickwork2 by W.G.Nash.

 

[worms]

I'm notorious for looking at leadwork as I'm driving around, well glancing I should say and I've even missed the odd mini skirt now and then. :shock:

I missed a turning yesterday because I was too busy trying to assess the proportion of buildings in a particular location that had roof snow boards (that I mentioned on another thread) and whether they would be visible on Streetview from the hill opposite!

 

[agbagb]

Pots and Liners done:

The flaunching ended up being around 10" in OPC with rubble added to bulk it out. Brick ties went in the morta joints of the re-built courses and a couple of steel bars went across the top under the liner top plates.

It all looks very sturdy to me, fingers crossed they will draw ok and last my lifetime

There is more details plus video of the liner instalation if anyone is interested.

As for the roof. Stripped, rotten timbers replaced, breathable sarking membrane on, slatted, dorma cheeks leaded. If the weather holds we should get some tiles on this week. I've spent the last two weekends taking advantage of the scaffolding at the front to remove the OPC ribbon pointing and re-pointing with "brushed back" 3:1 grit sand and NHL. All the high bits are done now, the rest I can leave until later and work off a step ladder.

We'll be having the OPC render taken off the back and possibly re-rendered in NHL. It might depend what condition the stone and brick work is in.

After a year all this progress is making me dizzy but aleast my wallet is getting easier to carry around. (Just for record, if anyone is reading for the scaffolding interest - The skiny scaffold at the front, 5 board round the back and chimney scaffold cost around £1000)

I've done a "One year on guided tour" video (a bit shy to post a direct link but you can find it from the blue dot).

Andy