Fireplace constuction

[Ukcat]

Hi I am fitting a inset/cassette stove into my original brick opening (1930 house) the current opening is approx 800mm wide by 900mm high so I need to build up to reduce the opening and create a smaller one for the stove to slide into. I'm not exactly sure what to use for this. I originally planned to use concrete blocks but the manual says that the unit can transfer quite a bit of heat into surrounding structure. Would concrete blocks be ok or is there a more suitable option. The manual states to leave a 5mm clearance gap around the insert. Also thought about lining the inside of the opening with some insulation board to protect the blockwork. Any advice is very welcome

 

[begreen]

What is the make and model of the cassette insert?

 

[Ukcat]

What is the make and model of the cassette insert?

Hi it's Stovax riva 40

 

[begreen]

Thank you. The floor of the cassette will be the coolest part. It has an ashpan and healthy space above it to the firebox floor and grate. I don't think there will be an issue with the concrete blocks as long as they can be securely anchored into through the floor of the cassette body. If properly made, the exisitng fireplace floor was designed to take the heat of direct contact with the hot coals of a fire.

When forming the opening, the manual recommends one use insulating blockwork to reduce the heat transfer to the external walls. It also recommends that if you are in any doubt about your ability to produce a safe opening contact your Stovax dealer for professional advice.

 

[Ukcat]

Thank you. The floor of the cassette will be the coolest part. It has an ashpan and healthy space above it to the firebox floor and grate. I don't think there will be an issue with the concrete blocks as long as they can be securely anchored into through the floor of the cassette body. If properly made, the exisitng fireplace floor was designed to take the heat of direct contact with the hot coals of a fire.

When forming the opening, the manual recommends one use insulating blockwork to reduce the heat transfer to the external walls. It also recommends that if you are in any doubt about your ability to produce a safe opening contact your Stovax dealer for professional advice.

Hi Thanks for the reply I have just poured a new concrete hearth which is approx 300mm thick so I think this will suffice. For the base I also plan to add quarry tile over the concrete which should give extra protection I've attached a couple of pics to show current situation. I've also fixed in a new lintel. I'm confident about building up the enclosure but not on the type of brick/block. I've seen the mention of insulated blocks but not sure what these are hence my plan to line the enclosure with 30mm insulation board. I have contacted 2 dealers and neither mention about the need to add insulation to the recess

 

[begreen]

That looks very shallow. The cassette is much deeper, 350 mm. Is the plan to build it out another course of bricks? Will the flue liner align properly?

 

[Ukcat]

That looks very shallow. The cassette is much deeper, 350 mm. Is the plan to build it out another course of bricks? Will the flue liner align properly?

Ok so depth at moment is 350mm (brick and a half plus a joint) front will be boarded and tiles which will add approx another 50mm so should have space. Pic shows original 1930s fire so it will finish up similar but with new tiles
Flue will line up perfect

 

[Ukcat]

Hi here my 2nd question. So I am fitting a 5kw inset stove and plan to tile around the stove . Um using the correct tiles and heat proof adhesive and grout but my question is I need to pack the tiles out from the wall. I'm aware that the area above gets very hot and that normal plaster would not be suitable.what type of product would-be best here ie is cement hardbacker suitable for directly above the inset and then tiles on top

 

[begreen]

Hardibacker is a brand. It has some cellulose fibers in it. For peace of mind, pure cement board should work but not sure what brands are sold in England.

 

[Ukcat]

Hardibacker is a brand. It has some cellulose fibers in it. For peace of mind, pure cement board should work but not sure what brands are sold in England.

Ok thanks. We have a product made by vitcas (insulation board) which would be suitable but the munimum thickness is 30mm. this would give a total of approx 50mm. (Board adhesive 6mm + board 30mm + tile adhesive 4mm + tile 10mm) Which would put the front of the flue spigot 10mm further back than my lintel. Cannot see any info to say this would be a problem as everything is non combustible

 

[begreen]

Yes, I found a Vitcas Fireplace Construction Board. If non-combustible and suitable for tiling it should be ok. I also see there is
Cembloc CemBacker 12mm Fibre Cement Tile Backer Board that comes in 6mm and 12mm thickness too.

 

[Ukcat]

Yes, I found a Vitcas Fireplace Construction Board. If non-combustible and suitable for tiling it should be ok. I also see there is
Cembloc CemBacker 12mm Fibre Cement Tile Backer Board that comes in 6mm and 12mm thickness too.

Thanks for the info. At least I have a couple of options. My choice will depend on how much flex I have in the liner. It's a 125mm mid tech dragon flex 316. I have no experience in how much play can be achieved . Idealy I will be able to get the liner to deviate back by about 20m over about 150mm but not sure on how rigid it will be

 

[Ukcat]

I'm just about to start bricking up to create new enclosure for inset stove pic shows roughly where bricks will be and trowel is were stove will eventually be positioned. The base is concrete but needs raising up by about 30mm which I planned to screed with grit sand and cement. Question is should I brick up and then apply the screed or screed the whole area and build onto the screed. Thanks in advance

 

[begreen]

Merged to previous post for context. The picture in post #5 looks like the hearth is already poured.

 

[Ukcat]

Merged to previous post for context. The picture in post #5 looks like the hearth is already poured.

Ok thanks. Yes I had a bit of a disaster when I poured the hearth I did the top inch of so in gritsand screed to enable a smooth finish but I mixed the wrong ratio so had to chop up the top layer hence the need to apply more screed