Venting a disused chimney

[malcolm]

I have a chimney in my barn where the fireplace has been removed and sealed, and the top has been covered by a paving slab. I pulled the top off this afternoon and it smells damp in there. Also there is evidence of cracking on the outside of the stack which may or may not be related. Here's a photo of me peering at the paving slab:

What's the form these days for sorting this sort of thing out? My approach might be to replace the paving slab at the top of the chimney with a victorian chimney pot (1850 to 1880 low status, suggestions welcome) with a vented cap. Flaunching in HLM 3.5 to reduce the chance of cracking. For the bottom venting on the outside - knock a brick out and replace it with an air brick.

Are there any obvious errors in there? And what do you sit the pot on? Slates or cement board? And if slates how are they arranged to allow a pot to be supported?

I'll need to take the paint off the chimney and the wall first which will take a few days, and there might be a little rebuilding work as the tree in the photo is not the first to be resident there. There was a triffid on the chimney once.

 

[88v8]

Yes to all that. Depending whether the chimney has been truncated, you might find the top is already capable of supporting a standard pot.

Not sure that NHL 3.5 is man enough to withstand the weather. Someone did post a flaunching mix on here but foolishly I didn't save it.
Think cement was involved.

Low status... errrm
http://www.ebay.co.uk/itm/CHIMNEY-POT-SQUARE-/281285407618?pt=LH_DefaultDomain_3&hash=item417deab382

or?
http://www.ebay.co.uk/itm/CHIMNEY-POT-COLLECTION-FROM-ORPINGTON-KENT-J4-M25-/271424624051?pt=LH_DefaultDomain_3&hash=item3f322b15b3

Given that you're going to cap it, square pot probably not such a great idea.

Ivor

 

[Penners]

As regards ventilation, your plans look fine to me.

Slate is good base for the pot to stand on, although cement board may be preferable because it's easier to cut a neat hole in it, slightly smaller than the pot

For the flaunching, I would use a cement mortar - probably 3:1 with the sand a 50/50 mixture of building and sharp sand. Despite the universal revulsion against cement on this forum, I believe it does have its uses, and this is one. I would incorporate some galvanised wire netting or mesh in the flaunching, to reinforce it. Make sure you finish it with a good incline to shed water, and trowel the surface well.

 

[malcolm]

Thanks, excellent instructions make it sound very straightforward. I'll use cement for the flaunching and NHL 3.5 for repointing or resetting bricks. It'll be the first time I've done this sort of thing. One of the more scary bits will be raising the scaffold tower another level. I'm very bad with heights.

I removed the ugly light and started paint stripping phase 1 today.

 

[Zebra]

How did paint stripping going malcolm? It was a lovely day here, so I assume you had good weather too?
(Hopefully you're able to come to the computer, and you're not clinging to the top of the chimney in a fit of vertigo?)

 

[malcolm]

The paint stripping isn't going brilliantly. The paint is 6 layers thick in places and taking some time to remove. I've started so can't really stop but I'll get there really really slowly. I'll employ more of a conservation strategy on the other, larger gable (just scrape the peeling bits off and leave the rest well alone).

I cleaned the paint out of the mortar joints on the chimney. The mortar is made of earth with tree roots in it. The horizontal line 3 bricks down is a triffid which has lifted the upper courses of the chimney by 1/4 inch.

 

[Penners]

It'll be the first time I've done this sort of thing.

At the risk of sounding patronising, I should perhaps explain my comment about trowelling the surface of the flaunching well. Trowelling mortar brings the "fats" to the surface, with helps to seal it against water ingress. So a well trowelled mortar will shed the water better.

I've started so can't really stop

I'm exactly the same with Maltesers.

 

[Zebra]

Well, hope it starts to go a bit better with the paint stripping. Know what you mean re: can't stop now - I found a loose brick in my chimney, pulled it out, and when I'd found out how to do lime pointing and put it back in, I realised that the rest were loose too and I'd have to do the whole lot! Several weeks later, a sturdy and nice chimney. But stress and hard work on the way. Keep going, you'll get there!

 

[malcolm]

Thanks Penners - that is useful info and not at all patronising. I've no idea what I'm doing really but will figure it out before I actually do it.

Paint stripping is going reasonably jut really slowly. Seems the trick is to tackle it one coat at a time. I have a little patch nearly finished without much damage to bricks (yet - though that bit was badly adhered and just fell off):

The chimney is a bit more exposed and has spalled a bit. Might put the roof ladder up and snip the triffid again soon. You can see the root in the top middle of the photo. Goodness knows how much tree I'll find inside the chinney.

 

[Feltwell]

My own "triffid" experience, a silver birch merrily trying to grow out of my chimney, would suggest that you shouldn't snip it but should poison it instead.

My ladders wouldn't reach said triffid, so I arranged for the window cleaner to come round with his extra, extra long rope-operated ladder. I went up there and snipped it, thinking "job done". Bloody thing regrew within 2 months, next time I went up armed with a spray bottle full of Roundup weedkiller, that finally persuaded it that it wasn't wanted!

 

[malcolm]

My strategy is to remove the top 3 levels of brick working from the other side and remove the triffid together with it's root system. I think it's a climbing plant similar to the one we removed from the opposite gable. Probably does make sense to kill it first just to be on the safe side.