Fireplace installation

STEVIEP74

Hi just looking for some advice before starting the above job, I am renovating an old house.

1. What mortar mix is ok for hearth installation, and is normal cement ok?
2. Do i need vermiculite for behind the fireback, loose or mixed?
3. Do i need a fire rope for the side of the fireback?
4. Anything else worth knowing?!

Thanks in advance,

Stephen

Calahonda52

Welcome to boards.
Stephen, IMO, your questions may point to a lack of appreciation of what happens if the install goes wrong and you end up with CO fumes in the house.
The right materials are not in question, its the workmanship

antiskeptic

STEVIEP74 wrote: »

Hi just looking for some advice before starting the above job, I am renovating an old house.

1. What mortar mix is ok for hearth installation, and is normal cement ok?

By "hearth" I take it you mean the slab/tiles on the floor on front of the fireplace? I've used tile adhesive and it's lasted for years. Easier to bed in than mortar. For the surface directly under the grate, standard 3:1 mortar has been successful but you would want a decent thickness (an inch and a half). A skim on top of what's there will crack.

2. Do i need vermiculite for behind the fireback, loose or mixed?

I've used vermiculite and my new fireback slightly cracked - even though gentle fires to start with. The old way was to fill with stone (judging by the 3 or 4 fireplaces I've pulled out) This makes sense: you want to sandwich the fireback between something robust (like stones) and a cast iron front. Without locking the fireback to anything. Leave it somewhat free floating and the fireback can expand and contract freely and won't crack. Constrict it by locking it in and it is more likely to crack. Vermiculite isn't constricting. But it's not robust like stone. And it's pricier. And they didn't have vermiculite in the day when they were alot more familiar with building fireplaces than we are now :(I'm thinking of my 100 year old rendered gable which faces southwest and into the weather. Weathered but crackless. The neighbours 10 year old cement rendered version directly across the road is cracked to bits)

3. Do i need a fire rope for the side of the fireback?

You mean between the vertical face of the fireback edges and the cast iron front ope edges? No point. What are you going to do to seal the area above the fireback?






4. Anything else worth knowing?!

A few things.



A word on draw (updraught).


- imagine there is no cast iron front on the fireplace but your fireback and grate are in place. How does the fire work now?

I'm supposing the installed fireback stops short of the total opening height (maybe there's a horizontal head or an bricked arch a distance above the fireback). Assuming the head/arch isn't miles higher than the fireback, the fire will still work fine: there is a draw (negative pressure) which sucks air in at all points of the opening and nothing leaks out. Try it: buy a packet of Marlboro (if you don't smoke), puff some smoke (but don't inhale or you'll get hooked) at various points at the perimeter from a distance of a foot away, without the fire lighting, and see does the smoke get pulled into the ope. If it does you have a good draw which will work fine when the fire is lighting even without the cast iron front.


- what does adding a cast iron front onto things do in a technical sense? Assuming the cast iron ope height is lower than the head/arch heightd of the bare fireplace then you will improve the draw since you've reduce the ope area on which the draw acts. If the fireplace works without the cast iron, it will work with the cast iron, only better.



That said. I'm on the internet, not in your house. And we're dealing with fires. Stopping smoke leaking out is a function of draw. A good draw and there is no technical need to seal the cast iron anywhere. If the smoke is leaking out such as to get behind the cast iron and leak out between it and wall then you've draw problems that sealing the cast iron to wall isn't going to solve - the smoke will simply leak out on front of the cast iron and into the room

It's normal practice to set the cast iron against the brick behind the plaster on the chimney breast, not simply nail it against the plaster (and silicone around it as I've seen done). So:


- put your fireback loose in place

- set a spacer on the hearth base (hearth not fitted) to take account of your hearth thickness (stone or tile) plus adhesive, say 10mm for the latter)

- If there are lugs on the bottom edge of the cast iron, grind or file (don't, just invest in a 4" grinder) them off, level cast iron vertical and horizontal. Pencil a line on the plaster around the cast iron and remove cast iron. Chip plaster away. Set cast iron against wall

- usually there are fixings only at the top of the cast iron: a lug each side. And nothing on the bottom. Concrete self tappers (torx head) are a great way to anchor to the breast at the top into brick. Tough if your lugs match a mortar line in which case long threaded bar and chemical cartridge (it doesn't get hot around there) with a nut to finish when dry

I drill holes at the bottom and concrete screw there as well - you don't notice them when things are finished with some heat proof paint later. If the breast isn't level in the vertical, space with some metal strips between touching edge of cast iron and wall (galvoband is good as you can build up thickness easily) before finally tightening conc screws. You might need to chip more plaster locally to fit the metal packing

- you've now got a level cast iron fixed to breast and a loose fireback. Pull the fireback til it's snug against the ope edges of the cast iron. Pack the fireback with panel pins or nails on the bottom if you need to level it to get a nice match with the cast iron but don't fret if the gap varies a bit: cast iron fireplaces weren't made to tight tolerances and you're not reliant on a seal for smoke or anything

- back fill with stones, beach stones are a good size. (I forgot to mention: run a
few layers of of duct tape around the back of the fireback at the top. For reasons which will become clear.) You're looking to create a steep slope of stones 40mm or so shy of the top of the fireback running uphill to the back of the chimney structure. Pour mortar on top of the beach stones to create similar sloped surface between top of fireback and chimney proper. The steep slope stops soot building up (which would occur on a flat surface and could catch fire). The duct tape stops the mortar bonding to the fireback - the duct tape will burn away

- You've now got a floating, well contained fireback and a level cast iron fireplace in situ.

- Your hearth. If you fit a solid slab of stone it will crack: the bit under the grate will get hot, the rest stays relatively cool. Differential expansion= crack. The way around this is to:

cut the stone in half over it's length (length being breast widthways). Lay the two halfs in position - cut line will be in the centre of the grate. Now mark out a rectangle over the two halves: width of grate long (breast widthways) x 4" deep (starting from grate and measuring out). Cut that rectangle out. You now have four bits - two large rectangles with square pieces out of the corners closest to the grate. This allows for differential expansion.

If tiles then similar arrangement

lay the hearth, working the stone under the cast iron, right into the brick of the breast. Grout

- duct tape (couple of layers thick) bottom edge of fireback and lay mortar under grate area. Same reason as above for duct tape

- plaster around cast iron perimeter

- gentle on first few fires: wood, briquettes, few bits of coal etc. Make sure your fireback is a bit aged. If you don't know, it could be fresh out of the mould so go very gentle with fires for a while.



If you've fitted the cast iron already then so be it. Do the hearth as mentioned just pushing it tight against the cast iron and infilling under grate with mortar. Check your draw is good and you won't have issue with leakage past the fireback/cast iron interface.




Oh.. and invest in a CO alarm for the room. Google the folk who died when a multipack crisp bag was chucked on a dead fire, didn't burn but uncrinkled, floated up like a parachute, blocked the chimney and killed them