Filling a large hole in chimney flue

smiledotcom

See pic.

I have removed a gas fire from the living room and I want to restore it to use as a "real fire". (The gas pipework has been removed and capped off).

I originally thought to knock out all of the "funnelling" that had been applied and bring the whole thing back to the original rectangle of brickwork but I just couldn't get the pickaxe in there so I'm now left with a part-demolished "funnelling" which I want to restore (you can probably tell that I'm not a DIY-type person. I'm just doing the best I can whilst I'm time-rich-cash-poor...)

Anyway, I'm now left with some sizeable holes (one about 3 fist sizes) that need to be refilled. I just don't know what to fill them with - lots of conflicting advice on the websites.

The guy who came in to sweep the chimney after the gas fire was removed advised me to fill the holes with a mix of 4 parts sand, 4 parts cement and 1 part lime.

Other advice I had was to fill the holes with a lime mortar mix: 3 parts sand, 1 part NHL 2 hydrated lime. I mixed this up yesterday and part filled the smaller holes with this yesterday but this morning I notice that the lumps of lime mortar mix that fell off as I was applying it have a VERY CRUMBLY TEXTURE and I just don't see how this mix is going to withstand having coal and wood chucked at it. Surely it's just going to get damaged very quickly and fall apart once I start using the fire?

Please can someone advise me what to fill these hole with so that I end up with a smoothy funnel for the smoke to go up when the fire is in use.

I still have some natural hydrated lime left over (1kg of it) but I understand that this "goes off" quickly and will need to be used in the next couple of days!

I have various materials that I could use for this job: Sand, cement (Blue Circle Mastercrete) and the "rubble" that I originally knocked out with the pickaxe and broke tip into small chunks.

I also have a 5kg tub of ready-mixed firestone cement. Surely between this lot I can repair the hole in the chimney flue?

Tom99

[FONT=Verdana, sans-serif]Can't you use a brick bolster and 4lb hammer to remove the concrete either side rather then a pickaxe?[/FONT]
[FONT=Verdana, sans-serif]You could also use a masonry drill to drill holes near the edge of the concrete before chiselling it away. [/FONT]

smiledotcom

Thanks for your advice.

The funnelling extends for another 30-40 cms above the top of the opening and I found it quite impossible to swing a hammer through the opening and upwards with any kind of strength (7-stone female weakling here) to smash up any of the mortar that created the funnel.

It's also a really tight space to work in. Very little leverage.

Unfortunately, I don't have the masonry drill tool you've suggested and it seems to me that repairing the existing funnel would be the easiest, and most manageable way (for me anyway), to finish this job.

ian103

Or something like this

Tom99

I you are going to repair it I would think building sand and cement 6:1 or 4:1 should be fine. Not sure why you would require lime. If filling a small hole the wet it beforehand with a brush.

smiledotcom

Ive always been advised to have lime in the mortar because it's a fireplace

FreeBear

The OP needs to use a clay fireback with a suitable throatplate - https://www.installaflame.co.uk/clay-fireback-12-14-16-or-18.html - The decorative brick surround will need to be removed before the fireback can be installed. The space between the fireback & builders opening will then need to be filled in with vermiculite (some will just fill the space with rubble & mortar).

Stuffing a bit of mortar in there is a short term bodge.

As for lime mortar, I would have suggested a 2:1 mix of sand & lime (maybe NHL3.5). It should not be mixed with too much water, just enough to make a stiff paste. Soak the bricks several times over the course of a couple of days. When applying the mortar, it needs to be pressed in firmly, and as it dries, compressed with a wooden float. It will remain quite friable until the surface has hardened - This could take a week or more as it "carbonates". Allow a week per millimetre of thickness for it to properly cure.

Both lime mortar and cement will crack and flake off quite quickly once you start having a good fire in there. Without a properly sized throatplate, most of the heat will disappear straight up the chimney leaving you with just a flame effect. Before you waste any more time & money on this, consider installing a wood or multifuel stove - You can get some fairly attractive inset models and they would provide some real heat during the winter and be much more economical to run.

smiledotcom

Thanks for this advice FreeBear.

I looked into getting a wood burning stove but the installation, which would have required me to line the chimney flue, and purchase the wood-burner and hearth was prohibitively expensive (I live on the first floor of a 3-storey building. Wooden floors).

I think what you're advising me though is that I am not going to be able to do this DIY job myself using the materials I have (and that I'm going to need to get someone in to finish this job - and it's probably going to cost me ££££s to do so!!!). Sigh.

FreeBear

With an open fire, you will still need a hearth of an approved construction. If you don't have one at the moment, you need to stop and rethink your plans.


You would need to be compliant with building regs, and I suspect reinstating an open fire will need to be signed off by building control. With that in mind, perhaps installing a stove isn't as hideously expensive as you imagine compared to an open fire...


Throwing in another curve ball - From your comment about living on the first floor - Is this a leasehold flat ?
If so, you'd probably need permission to install a stove or open fire from the freeholder. That is going to add to the costs & headaches.