Anyone have any advice for rendering a fireplace?

Conrad

Sorry, didn't know if this is the place to post this.

Had a look round the net and youtube and so far not finding what I need (Tommy's trade secrets on youtube are hopeless).

I am rendering an internal fireplace using sand and cement which I'm applying to the awkward internal space. The existing surface is rough brickwork and sandy cement which is a real mess.

It was incredibly hard to get my homemade render mix to stick - although I found spraying the dry surface with water helped a bit.


Did first coat yesterday, but if I touch the surface now, sand falls away - it's very brittle and loose. This is a worry perhaps? Or maybe it will go hard in a few days? It has a bit of a cement grey look I don't like.



Before I aks the following questions, please note I do not want a nasty grey finish. I want a nice mellow sandy tone, not orange, but a bit like Cotswold stone if you will.


Question 1 - what is the correct proportion of building sand to cement? One plasterer on the net says 6 or 7:1. I was doing about 4:1 yesterday. He is talking about rendering to plasterboard I think.

Remember I dont want a concrete grey finish so I'm wary about adding too much cement. My 4:1 mix is alreay grey!

Question 2 - how wet should the mix be? I found if too wet it fell away. So I ended up with quite a dry mix. Is this why this morning it seems brittle and loose?

Question 3 - does one need to add a plasticiser such as Febmix?

Question 4 - what type of building sand (or other sand) should I use for the top coat so I get this nice Cotswold sandy finish?


Cheers

Leif

What is an internal fireplace? Can you describe the fireplace more. If you mean an opened out builders opening used for a wood burning fire, then I was told online to use a lime based mortar, as it resists heat better. I also spoke to a plasterer and some fireplace installers, and they said the same thing. Yes mortar does seem to be soft at first. My understanding is that increased cement leads to a harder but more brittle mixture.

Conrad

Leif wrote: »

What is an internal fireplace? Can you describe the fireplace more. If you mean an opened out builders opening used for a wood burning fire, then I was told online to use a lime based mortar, as it resists heat better. I also spoke to a plasterer and some fireplace installers, and they said the same thing. Yes mortar does seem to be soft at first. My understanding is that increased cement leads to a harder but more brittle mixture.

Thx

yea, it's an old fireplace opening, just decorative, no longer containing an actual fire of any kind so heat is not an issue - it's quite small and not suitable for a fire of any kind really.

quidsinquentin

Your mix is off IMO. Can't remember the correct ratio, but as long as the surfaces are clean - of soot, etc - and you have some purchase in the gaps between the brickwork, it should stick even without the glue/plasticiser.

I've done this years ago, twice IIRC. And it worked first time, but my brother was a plasterer/bricklayer and he told me what the mix was. Actually, now I think of it, I may have plastered it! It was my first house purchase and several decades ago.

But I did render the old coal chute with a sand/cement render.

Sorry C.