fire and lime

[charlie-ia]

our chimney has been lined fairly recently (sometimewithin the last 20 years but barely used, cos its still clean)
the liner stops about 4foot from the floor. the back of the fireplace is normal bricks which have been slightly damaged by fires. there are no firebricks as i recognise, or any kind of grate or anything. the rest is either sandstone (with some loose stone) or "origional" concrete. there is an ash pit in the floor, and a very rusted bit of hinged metal grid to go over it.

it looks like nothing has been done to the fire place in the way of repair in many years, and the repair around the flue liner just stops about chest height.
what do you use in the hot area around the fire? i see chimney cement in the diy shop and think that looks just the thing, but i now have "no cement" branded into my brain.
we are still considering wether or not to get a range, which would have to go in the fireplace( i assume? )so we want to be able to use the actual fire, at least untill we have cremated most of the worms, but dont need any thing fancy.
do we need firebricks too? how far should these extend?
the chimney leaks badly through a patch of loose stones into the next room. if we repair that with normal lime, do we use the same inside the chimney?

 

[Craig]

I had a "fireplace installation specialist" do a fireplace for me and he used bog standard second hand london stocks and normal cement, though he promised to use lime, so I would say you can use normal bricks and lime render/mortar.

 

[Mark]

How does the liner stop and what sort of liner ?

Is there a gather ? (sort of inverted funnel to get the smoke to go up the chimney ?

Are you sure there hasnt been a stove fitted which has been removed?

Any sign that a fireback has been used ?

 

[charlie-ia]

clay pipe, perhaps 6"-8"
it is very likely there was some kind of range or stove. no idea what to look for
i assune ther would be some clue? are liners different? will it affect us just having a fire for now if its for a stove?
the liner just kind of stops. cement fills the gap between liner and flue and has a smoothe edge. i cant remember if it curves up or down.it could easily be made into a funnle shape with a bit more cement. it just finishes where the flue finishes. then the chimney opens out to the fireplace. its all a bit rough. on the other side of the wall the fireplace is blocked up and cemented from floor to ceiling just smooth (the hearth is there and the original surround leans against the wall)
where we assume the two flues joined, just below the endof the liner and cement are two new breezeblocks. theyre nicely fitted, but no cement has been used. this is where the smoke leaks into the cupboard, the stones are loose in the back of the cupboard, but nothing too scarey.(i think-do correct me if im wrong!)
we're tempted to leave the breeze blocks in place as the walls are mortered "random rubble" and they seem to be doing a good job.

what kind of lime mortar should we use? ive just been on a lime day, and my head is spinning with all the different types!

 

[Mark]

Well the first issue would be the size of the open flue and the amount of flow it will take. 6 or 8 inches is not very big ?(as the actress said to the bishop)- fine with a stove (which has a restricted air flow and only allows the smoke to rise into the flue) but you will probably find that an open fire will fill the room with smoke. This will especially be a problem if its a big fireplace (and it sounds like it is).

Sounds like you have a clay liner surrounded with that insulating concrete (vermicelulite or whatever its called) - is it very lumpy and light ? My guess is that the bottom bits of breezeblock are just what was put in to block it off when the stuff was poured down the chimney (or built if the stack is newer)

I wouldnt be happy with smoke getting into a cupboard - fire risk apart from anything else.

I have stoves and just bog standard 3:1 sand/lime mortar lining the openings.

 

[charlie-ia]

once we tried the newspapaer up the chimney trick, the smoke in the kitchen wasnt too unbearable, but as you say, the cupboard in the other room is a fire hazard, and smoked a lot.(didnt help that i was in the cupboard exploring, having left a gentle fire of clean wood. whilst i'm in there He's got a raging inferno of godknowswhat going!)

if the fire draws ok, is it safe to use a stove/range flue for normal fires?
how big should a fire flue liner be?

the breeze blocks (2) are set into the wall to fill a hole, rather than blocking the flue, holding up the rubble walling

so there isnt a cement-free fire-cement that im looking for then?
if i render the fireplace woud i need firebricks too? the bricks that are there have clearly been damaged by fire and will need protecting some how.

how long will i need to leave the lime to dry before having a fire? and how long after that before we can have a big fire?

 

[Mark]

Maybe you'll be OK.

I think there is a chart of chimney to fireplace sizes in the building regs. but if it draws ok then I dont see the problem if it is swept regularly.

If you want to keep the bricks I would just repoint (maybe replace any bricks that are beyond hope) and use a fireback. I left the mortar to dry for weeks - but that was down to doing it in spring and not needing to light a fire (and in the other room not yet having the stove to put in)

the only thing I used fire cement for was the joints in the metal flue pipe.

 

[MdB]

I think there is a chart of chimney to fireplace sizes in the building regs. but if it draws ok then I dont see the problem if it is swept regularly.

I wanted to know this myself so looked it up.

This doc, Section 2.7 and Table 2 states an open fireplace has to have a flu of 200mm diameter for up to 500mm x 550mm fireplace openings. Larger than that requires a flu cross sectional area 15% of the opening size. Read the doc for full details.

 

[charlie-ia]

thats a lot of reading! thanks though, very usefull

 

[Lime]

If an enclosed controlled-draught fire is fitted to this chimney the danger of death by carbon monoxide poisoning would be very high.
The chimney must be fume-tight and needs to be lined throughout it's length.

 

[NT]

Wood only fires are ok with no fire bricks, but coal burns hotter and needs some form of lining.

Most chimneys arent lined and work fine. Any leaks should be sorted though, and your narrow opening may make open fires unworkable, but iron stoves are available.

The fire cement in tubs in the sheds is dreadful stuff, and overpriced too. Lime's way cheaper.


NT

 

[Penners]

A 6" diameter liner is unlikely to be sufficient for an open fire.

I reckon you're correct when you assume that it was installed for a stove or wood burner of some kind. This would have had an insulated steel flue for the first couple of feet or so, that then attached to the clay liner.

Installing a woodburner would presumably enable you to use the chimney in its present form, and would remove the risk of smoke bleeding through from the fireplace into adjacent areas (assuming that this is happening below the height of the liner).

But make sure it's installed by a specialist who can (a) check that the liner is intact and effective, and (b) make sure the attachment of the flue to the liner is kosher.

I presume the fireplace is big enough for a stove?

 

[MdB]

I've started to think about sorting out my two fireplaces and was wondering if (a) lime mortar is ok for repointing inside the chimney and (b) if limecrete is okay for the hearth? We will be fitting tiles, slate or stone on top with a fire basket but I'm worried about the lime getting heated up and turning back into quick lime. Am I worrying too much? Are the temperatures too low for this to happen? I have a bit of a damp wall and want to use lime where possible but I don't want anything fizzing if it gets wet. I'll probably get these guys (http://www.chimneysweeps.co.uk/) in to discuss the works before I do anything but would like to know what I'm talking about first if possible.

 

[NT]

I think lime takes in the region of 1000C to revert to quicklime, and cement even higher. So the cracking up issue of OPC in fire use must be due to something else, I'm guessing differential thermal expansion.


NT

 

[MdB]

I think lime takes in the region of 1000C to revert to quicklime, and cement even higher. So the cracking up issue of OPC in fire use must be due to something else, I'm guessing differential thermal expansion.

Wiki has it starting at 825°C which is glowing red hot sort of temperatures. Hearths / chimneys won't get anywhere near that sort of temperature (unless it is a really really big fire) so it won't be a worry. Thanks for posting.