Build a false chimney? Ive seen pictures of this but....

TheOriginalTableLeg · 21 Nov 2010

Cant find any info on it.

I want to have a wood burner in my home, and the flue would exit out through the top passing straight up and through the ceiling.

Instead of having the full pipe on show I would it to look as though it was a normal chimney and fireplace.

Does anybody know of this can be done? and if so, any idea of materials used?

The pictures I have seen appear to have a metal frame inside with what looks like a plasterboard material on the outside.

Any other options? Build it from bricks? or similar?

???

*edited to add: I do not have a chimney for the flue*

TheOriginalTableLeg · 21 Nov 2010

To add....

Building regs Part J give examples of a NON combustable wall as being of concrete, metal and plaster.

Could I therefore have a false fireplace made from concrete blocks with a concrete lintel across the front?

If so, does it have to be any particular concrete blocks?

hotrod · 22 Nov 2010

TheOriginalTableLeg said:
Could I therefore have a false fireplace made from concrete blocks with a concrete lintel across the front?

If so, does it have to be any particular concrete blocks?

I've seen it done with lightweight concrete blocks, but if I was doing it myself I would be using dense 7N concrete block.

The pictures I have seen appear to have a metal frame inside with what looks like a plasterboard material on the outside.

It's probably BG Gypframe or Lafarge GTEC studded out with heat resistant board like Glasroc/supalux/promatect. I'm going to be using glasroc on mine in a few weeks as it's less than half the price of supalux. OOI if it's a wood burner are you getting a HETAS installer to self certify or are you doing the BRegs notice?

Richard C is well clued up on this stuff, so fingers crossed he'll add his wisdom. Where are you Rich?

TheOriginalTableLeg · 22 Nov 2010

Thanks very much Hotrod for the reply.

To answer your question, at this moment in time I am considering my options with regards to having a Hetas installer do the whole job v's submitting b'regs and self installing.

I am confident that I can physically do the install myself no problem, but it would be making sure I use the correct materials etc. to comply with the reg's.
Aside from the obvious cost saving of doing it myself, I enjoy this sort of stuff!

Personally I like the idea of building a concrete blocked false chimney breast. With this in mind, does the lintel have to be any specific type?

Thanks once again!

TheOriginalTableLeg · 22 Nov 2010

Hotrod,

What about plastering the outside? Dot and dab standard plasterboard and then skim or would it have to be a different type of board?

And also, the inner visible section of the fireplace where the stove would sit.
Plaster sufficient here? Reg's say plaster is deemed non combustible.

???

Richard C · 22 Nov 2010

TheOriginalTableLeg said:
What about plastering the outside? Dot and dab standard plasterboard and then skim or would it have to be a different type of board?
And also, the inner visible section of the fireplace where the stove would sit.
Plaster sufficient here? Reg's say plaster is deemed non combustible.
???

Plaster is non-combustible but there is a big problem with Gypsum plaster & plasterboard products in that they are not suitable for use where temperatures regularly exceed 50 degrees C. I found this out to my own cost back in 2009 when I first got involved with plastering around stoves; gypsum will fail. Even some of the fire boards such as Fireline Glassrock etc. are only designed to withstand a one off exposure to fire, they are still gypsum based & not suitable if temperatures exceed 50 degrees C which it can quiet easily in the fire recess & the immediate area around the flue. Insulating between the flue liner & the chimney with Vermiculite will help a great deal here & also help maintain temperatures near the top of the liner to stop corrosive condensation & tar deposits.

Here a few links for you to read:
//www.diynot.com/forums/viewtopic.php?t=183614
//www.diynot.com/forums/viewtopic.php?t=211524
//www.diynot.com/forums/viewtopic.php?t=242738

This one in particular deals with suitability of some fire lining boards;
//www.diynot.com/forums/viewtopic.php?t=224751

Hotrod; I would reconsider the use of Glassrock, it’s still gypsum based; you need to reconsider using Supalux, its suitability as a boiler backing is why it’s twice the price of gypsum based fireboards whatever their make.

Some of the above links are also cross linked but you should get all the info you need; come back if you need to.

hotrod · 22 Nov 2010

Richard C said:
Hotrod; I would reconsider the use of Glassrock, it’s still gypsum based; you need to reconsider using Supalux, its suitability as a boiler backing is why it’s twice the price of gypsum based fireboards whatever their make.

Cheers for that Rich. This is the board I was going to use:-

Glasroc F MULTIBOARD 12.5mm

I've just read the attached PDF and limitations of use state, "Glasroc F boards are not suitable for use in temperatures above 49°C, but can be subjected to freezing conditions without risk of damage"

I've not worked it out yet but I reckon I'm going to need 3* 8'*4' sheets, Glasroc F is £47 a board, supalux £110 that's some difference. You can see why I want to use the Glasroc F!

TOTL need to rush off now so not had chance to read your post properly but will post back later. Cheers guys.

Richard C · 22 Nov 2010

hotrod said:
This is the board I was going to use:-

Glasroc F MULTIBOARD 12.5mm

I've just read the attached PDF and limitations of use state, "Glasroc F boards are not suitable for use in temperatures above 49°C, but can be subjected to freezing conditions without risk of damage"

Glasroc F is £47 a board, supalux £110 that's some difference. You can see why I want to use the Glasroc F!

I understand & sympathise with the reasoning but Fireline, Multiboard etc is often mistakenly chosen for use around stoves/fires etc. on price comparison with much higher spec boiler lining board & on the basis that if it’s a "fireboard", it must be OK; but it's only designed to give the specified fire protection in a “one off” fire incident. Being gypsum based it won’t stand continual exposure to high temperatures & won't fair any better than ordinary gypsum wallboard. A read of the data sheets will confirm this; BG say 49 degrees C (seems a strange figure to pick!) & there may be some margin in there but if it fails & falls off, your back to square one; just feel lucky that I picked up on it.

hotrod said:
I've not worked it out yet but I reckon I'm going to need 3* 8'*4' sheets,

I think you need to think about it a little more, you only need to protect the high temperature areas. This is usually the fire opening & the chimney area in the immediate vicinity of the stove around 800mm above & 300mm either side of the opening is usually sufficient (but don't go slapping gypsum Multifinish on it), for the rest of it you can use standard boards.

TheOriginalTableLeg · 22 Nov 2010

Richard and Hotrod,

Thank you both very much for the information.

I am reading through it as we speak, but I suspect I will have some more questions at some point.

TheOriginalTableLeg · 22 Nov 2010

Richard,

A lot of information.

still a bit confusing though. Perhaps youcould answer thismore directed question?

In a nutshell, what would be the preferred way to accomplish the following?

False chimney breast using concrete blocks with concrete lintel and finished with a smooth outer and internal finish to match walls.

My wife doesn't like a brick finish and wants it to look like it is part of the walls i.e. appears to have a smooth like plaster.

hotrod · 22 Nov 2010

Richard C said:
I think you need to think about it a little more, you only need to protect the high temperature areas. This is usually the fire opening & the chimney area in the immediate vicinity of the stove around 800mm above & 300mm either side of the opening is usually sufficient

I thought you may say that 3 n.o. boards was excessive - but there was method in my madness

. It's not for a stove installation BTW.

Rich, I'm mindful of hijacking TOTL's post so I'm sending you a friend request so I can hopefully pick your brains on this install via PM. I'm going to get my Gassafe guy to do the fire installation but I'll be doing all the building work. I would just like someone to bounce a few ideas off re combustible materials / plaster selection / insulation / clearances etc as I've not done this work before and it's for my own house. Hope that's ok with you.

hotrod · 22 Nov 2010

TheOriginalTableLeg said:
False chimney breast using concrete blocks with concrete lintel and finished with a smooth outer and internal finish to match walls.

My wife doesn't like a brick finish and wants it to look like it is part of the walls i.e. appears to have a smooth like plaster.

You can do that no problem. You just need to use a suitable heat resistant plaster on the areas adjacent to the stove. Victas is one that is mentionned frequentley on here:-

http://www.vitcas.com/VITCAS_Heat_Resistant_Plaster_Instructions.pdf

http://shop.vitcas.com/vitcas-heat-resistant-plaster-16-p.asp

TheOriginalTableLeg · 23 Nov 2010

Thanks Hotrod.

To summarize,

Concrete block 7N chimney breast with concrete lintel.

Then pva'd and a coat of Victus screed.

Then a top coat of Victus plaster.

This should be sufficient for all of the external block work of the fireplace and also in the opening around where the stove sits on the hearth.

This right???

And is this the best option?

I can tile the back of the opening as another option? or not?
If so, do they have to be special tiles?

I just need to weigh up all the options.

Any boarding or tiling I can do myself but as far as plastering concerned I have only ever been the 'mixer' for big plastering jobs.

I really appreciate any advice you guys can give me.

TheOriginalTableLeg · 23 Nov 2010

Oh and what about insulation?

I plan to use Twin walled flue from the stove, so therefore expect to have less heat passing to the surrounding false chimney breast.

Any comments here?

Richard C · 23 Nov 2010

TheOriginalTableLeg said:
Then pva'd and a coat of Victus screed.

Or you can use sand/cement/lime render (5:1:1) 2 coats, mix first coat thinner than the second; don’t PVA the blocks, just damp it all down very well but use PVA on the screed before applying Vitcas plaster; it also behaves differently to Multifinish. Make sure you read the links I posted & any cross links as there is a lot of info including the use of lime render (as above) & even lime putty.

TheOriginalTableLeg said:
I can tile the back of the opening as another option? or not?
If so, do they have to be special tiles?

Most tiles will take the heat but if you don’t use a cement based adhesive that will withstand the heat, they will fall off as well

TheOriginalTableLeg said:
Oh and what about insulation?
I plan to use Twin walled flue from the stove, so therefore expect to have less heat passing to the surrounding false chimney breast.

You should still insulate the space around the flue liner & the block work with Vermiculite, this will reduce heat transfer even more but, more importantly, maintain temperature in the upper part of the flue which is important to prevent corrosive condensate & tar deposits forming.

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Build a false chimney? Ive seen pictures of this but....

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