MortarThePoint

Do you think 75mm high enough for the flaunching on a 1.2m wide chimney stack with one pot?

I'll try to share some details. Correct about the Flemish bond.

The flaunching in general or if using with slate?

My honourary local conservation officer is in the kitchen having a cup of tea and not so keen on that type either

Yes I've assumed the worst case of it having a 200mm opening at the top. We're planning to fit a wire Tepee: A cowl with a lid would make a big reduction to the water entry.

I'm south of Cambridge. Thanks for the offer, the local merchant has some which is cheap and nearby. I've been staring at 3 trays which has felt weird. I have two as it passes through the roof line, then 1.8m higher is the top protection. My thinking has come down on the side of using slate for the following reasons: Not much water actually goes into the pot itself and a proportion of that would run down the inside of the pot and possibly be caught by a lead tray, the rest would go into the flue liner The pot sits snuggly on the pumice flue liner (could leave a gap but I'd prefer it snug) and Scheidel said the Isokern would absorb the water, so in reality any water draining down the inside of the pot will get absorbed by the pumice liner Spoke to Schiedel and they said it's not their default to recommend a lead tray at the top 'any more' The installation video doesn't have one. Building warranty are happy with slate It's easier and doesn't require fabrication I expect the mortar will key better to slate than lead(?) It's cheaper (but not if you consider the cost of a failed chimney ?) Thanks for all the advice @PeterW and @Declan52 on doing it in lead. I hope I'm not making a mistake, still open to persuasion.

This was one of the main reasons I decided against saving some money by using vermiculite rather than the Isokern recommended Leca. In reality I suspect it's a non-issue though as the total amount of rain that's going in to your chimney pot is probably around 0.1*0.1*3.141*0.6 = 0.019m3 = 19litres/year (climate data [1] [2]). Across a whole year that's not much and averages about 200ml per rainy day which is a glassful. You definitely need something surrounding your liner for support. [1] https://www.metoffice.gov.uk/research/climate/maps-and-data/uk-climate-averages [2] https://www.metoffice.gov.uk/research/climate/maps-and-data/uk-climate-averages/gcr9j7q0s

I like the look of that little meter. Do you have a part number?

I've had a response from my warranty provider to an email enquiring about this: "The DPC at the top of the chimney is an example of this, in that it would be needed to comply with the current building regs, however, it is seen as best building practice by warranty providers and serves a valuable purpose in preventing the chimney becoming saturated from the top down and in extreme weather will help to protect the chimney from excessive wetting and potential frost damage in winter. I can confirm that slate bedded to the top of the brickwork with adequate flaunching is one acceptable method of achieving the above protection." So looks like I could use slate and no lead. I'll be buying some slate anyway and will have to see if I can get the lead reasonably, but good to have the fallback of just slate. [PS: nobody here this morning so phoned brickie at 8am and he says he has an 'emergency on another job' so it will be tomorrow]

I did watch the video and it is tucked inside.. If you are using Isokern, it's worth talking to their technical support. They said the pumice liner is semipermeable and so lets the moisture out. They recommend the tray goes up the outside. I did see @PeterW's caution and will take measures higher up. There's a lead tray in already that bridges the cavity and I'll take a look at whether it's sagging

Need to be careful buying the Red Bank Canon as lots of places say they have it and it turns out to be the Contemporary Canon instead. Can't remember the codes, but essential to check before travelling.

£55+VAT each I think from Civils and Lintels. I need to track down the receipt.

The wedges are up the outside of the flue liner which passes through them and on a little higher. That means the brush doesn't get near them

May be cheaper to ask the truss designer to include a loading in the truss design. You could then use loft legs: https://www.wickes.co.uk/Loftleg-Raised-Floor-Loft-Legs---175mm-Pack-of-12/p/100412

I think this is where I have got to with the design now, a couple of options:. Is 75mm the right sort of height for the flaunching? The pot is a 600mm Red Bank Canon:

That made no sense, sorry. Really, I'd rather not use lead and use a couple of layers of slate and a stiff M12 type mix.

It won't fold up without all the little cuts. I won't cut the brim of the hat of course as the chimney isn't round. Around the liner is Leca fill which should support the lead. I could lay slate across the cavity to support the lead. I could also use slate on top of the Leca. Nearest supplier of Code 4 lead at this width that I have found is ~40 miles away unfortunately. Really, I'd rather not have the lead and use a couple of layers of lead and a stiff M12 type mix. Nobody has indicated that I can do that though.

A bit like this ?

That sounds simple enough

I don't understand, the upstand is about 100mm high

But the circular upstand needs to be welded on and I don't have oxyacetylene torch etc

@epsilonGreedy You have to tuck the upstand inside the flue liner in severe weather areas, elsewhere you can have it on the outside. @PeterW needs to be tomorrow, last two days for the bricky now and he's kept me waiting a month for them. The hard bit is making the circular upstand. If it wasn't for that it would be easy. Other trays already made so it's only the very top one that's a concern.

I not keen on using plastic. It would probably be fine die to Isokern but doesn't feel right. I don't have the lead for tomorrow. I could pick it up but I can't weld it. It's 1200x1050 with a cavity

Plastic dpc?

@Declan52 sorry to call you out, but do you have any thoughts on this as it's stressing me out.