Fireplace render / tiles

[john.s]

Hi,
I am nearly ready to finish off my fireplace - I am just going to sit a fire basket straight onto it, but as the brickwork is poor I want to render the inside - anyone know the best mix of lime/sand/cement? I understand it should be a weak mixture so as it doesn't crack when the fire is burning. Where do you get lime? None in Wickes as far as I could see. Should I render as far up into the chimney as is possible? The mortar looks a bit gappy.
Also - am considering tiling the inner hearth - can you use natural slate...or patio bricks? Or those small red natural finish quarry tiles?
thanks
js

 

[inwood]

I have two fireplaces which will also need rendering as you suggest. I will only be using sand/lime. Non hydraulic lime (putty) would be best to use but for such a small quantity it's difficult to find a local supplier. Alternatively get a bag of hydrated lime from your builders merchants (as fresh as possible), mix it with water in a large tub and leave it to sit for a couple of weeks and voila! lime putty (or a very close approximation to it).

Pretty much any tile would be suitable for tiling the hearth. The more traditional look would undoubedtly be the quarry tile but slate looks just as good - either polished for a more formal room or riven for the more rustic look. Most tiles should be suitable though (porcelain, ceramic, natural stone). Although if you're intending to use it as an open fire you'd probably want to seal the tile - with boiled linseed oil.

If you want to maintain a breathable floor I suspect the quarry tile would be best bed on sand/lime mix.

 

[john.s]

Thanks for the advise!
I thought I had heard somewhere that fireplace tiles have to be double fired or something to resist the heat. I think I will most likely go for the quarry tiles, I don't know much about them - they just look like a natural finish in a dull red which I thought would look good - and they are cheap and probbly quite easy to work with.
I think I will build the hearth up a couple of inches with some patio bricks I have seen then bed them onto that. What is the advantage of a breathable floor?
I'm still not quite clear about the lime - so it's effevtively a putty not a mortar? I'm sure the chimney sweep (sorry, "engineer") said to do a mix of cement lime and sand but I don't know the quantities.
js

 

[inwood]

John,

When I mention breathability I'm referring to the floor (or other surface for that matter) retaining the ability to absorb and release moisture (e.g. condensation). Lime allows this to happen but cement doesn't. Cement will trap moisture.

If your base is already cement then you don't need to worry about the lime. Just use a floor tile adhesive from B&Q or a cement based screed.

However if you're laying the tiles on earth then I'd advise using a lime mix. The lime and quarry tiles will also be permeable meaning that any moisture drawn up from the floor will be allowed to evaporate.

Lime putty is a term which refers to non-hydraulic lime (i.e. it won't set under water). It's called a putty because that's pretty much what it looks like. It doesn't set like cement (which has a chemical set), it only sets in the presence of air (through carbonation) which in hindsight means that it probably wouldn't be suitable for laying the tiles in this case (since no air will get to the mortar mix).

If you do need a lime mix it would be best to use a 'hydraulic' lime - so called because it will set under water (in a similar way to cement). Most builders merchants will sell a hydraulic lime (Travis Perkins definitely does) - it comes in three varieties, NHL2, NHL 3.5 and NHL 5 (NHL standing for Natural Hydraulic Lime). An NHL3.5 or NHL5 would probably be most suitable. The mix to use would be 3:1 sharp sand:lime.

 

[Andrew Bodenham]

John,

Bear in mind that your hearth must comply with the relevant building regulations, in this case Part J.
The Approved Document gives good advice on the construction and dimensions for hearth, and can be downloaded free.

http://www.planningportal.gov.uk/england/genpub/en/1115313928610.html

 

[inwood]

Thanks for that Andrew, a useful link for when I finally get around to finishing off my hearths.

 

[john.s]

Well, there I was at Wickes just loading up my trolley with bricks and tiles (after having carefully read through the building regs regarding hearth dimensions) and a friend phones. I told him what I'm up to and he says not to use bricks and tiles as they wont take the heat of from the fire basket, and that I should do everything in fire bricks and fire cement. Long story short there has been no progress on the fireplace since. Can this be right? I keep seeing pictures of fireplaces with fire baskets just plonked straight down onto brickwork etc - or are they just decorative ones and not actually working?
In the meantime, parquet flooring repair is underway...

 

[Nemesis]

Quarry tiles vary, but most are fired to a far higher temperature than a fire will emit.

Our stove sits on a hearth of quarry tiles and so far no problem.