Hi all

Hopefully someone cam help. I am building a false fireplace using thermalite blcks to house a woodburning stove. I am planning to render the inside of the fireplace with a 4:1:1 mix but I am unsure what to do for the outside. Should I use plasterboard and then plaster or something else. I have heard that plaster is not good with heat but don't know if this will be ok as its outside of where the stove will be located. Also what type of beading should I use for the cornering. Any help would be greatly appreciated - have attached some pictures of the fireplace so far.

Hello and

I would render the outside same as the inside mate. I too would use a 4:1:1 (plastering sand : cement : hydraulic lime) for your base coat then a 5:1:1 for your top coat. As for the beading i would use the standard rendering beads...

http://www.wickes.co.uk/External-Stainl ... nvt/224680

I would put your beads up first, then give the wall a good soak with water, get your base coat up and keyed, once thats up and firmed up top coat it and use the beads to rule off. Also while applying your top coat make sure the beads are filled all along each lenght.

For the finish I would just rub the render up to give a nice flat and smooth finish to paint on the inside and out

Thanks for the reply. I presume that I don't need to PVA because the blocks will give enough adhesion. Do I apply the second whilst the first is still wet (but firm) or do I wait for it to completely dry ? Sorry for all the questions but although I'm quite happy doing plastering, I have not done any rendering before and its like most things, you only get one go at it !

No problem. PVA isnt needed just give the wall a soak with plenty of water and you'll be fine.
As for the time frame I would put your beads up and scratch/base coat on day one then put your top coat and rub up on day two.
I dont think you will find rendering that difficult really, you got a decent float and feather edge?

Thanks once again, I feel a bit more confident about having a go now. I will have to purchase a decent float and feather edge .. any recommendations ? Finally two last questions I hope ... whats the best way to fix the beading when its thermalite blocks ? and also I presume when rendering the inside, I just have to use the beading on the outside as my guide for flatness on the inside?

I have a marshalltown rubber backed float...

http://www.amazon.co.uk/dp/B00002N5PQ/r ... B00002N5PQ

As for a feather edge the most important thing is to get one the right size for the job so you'd probly need a 4', I've known people use a straight piece of timber but i would recommend the real thing

I think you'd be fine just using clout nails to hold the beads in place while you put your scratch coat up then the scratch coat itself will hold it firmly in position for you top coat.

As for rending the inside you could put up a level screed in each of the back internal corners of your fireplace, let them firm up and use them with the corner beads to rule off


Any other questions just fire away mate...

Wonderful ... that's really helpful thank you. I thought I had covered all my questions but one came in the middle of night ... I have a large amount of builders sand left from doing the chimney ... can I use this for the render mix. I'm trying to keep the cost down as much as possible. I'm hoping that will be the last question and once again thanks for your help. I may even post a picture is it turns out ok ... or maybe it might be just a pile of muck on the floor !

I would strongly advise not to use builders sand for any rendering as it just isnt strong enough compared to plastering sand due to the very powdery texture of it. You will find some people saying adding builders sand to a plastering sand render mix helps give a smoother finish but i just dont see it myself and wouldnt recommend it.

I would be good to see how it turns out

Thanks for the tip about plastering sand, I don't want to have to do it again so will get this ... any ideas about the quantity. It looks like wickes do it in bags (can't see the weight though) or is it cheaper and in bigger quantities from elsewhere. I presume both coats are done with the plastering sand ?

Yeah both coats are plastering sand, they come in 25Kg bags and i would just get the bags from wickes unless its a whole house that needs doing.

Harder to say a quantity without being there tbh what sort of coverage you looking at?

cant see a flue for the wood burner???

_________________
we are all ------------------still learning

something else for you mate if you did want to plaster finish it use victas plaster its specially formulated to stay "sound" with tempretures over 50oc if you are v confident with your plaster finish this is what i would use, but it has to be done right first time round because once its set it is absolutaly rock hard and wont take a sand.
ive used this stuff plenty of times and it is good.
oh one last thing it also behaves differently to multi finish in the way that it tends to hang around more than normal multi so itll take a bit longer but that will give you plenty of time to get it right

Hi Guys

Thanks for the help, I think I am going to have a go with the render option only because this looks like the cheaper option although I am a little worried about the finished outcome. If it does go pear shape then I suppose I could plaster the outside or will the heat thing still cause problems ? It doesn't matter so much on the inside as I rustic effect is not always so bad there.

There is no flue as this is going in afterwards.

As long as you take your time on each section mate you should be fine.

If you take a look at this link...

http://www.ultimatehandyman.co.uk/PLAST ... LASTER.htm

Follow that procedure just swapping the wooden battens for the corners of the angle beads and the screeds you'll put up in the back corners until its level then once that's started to firm up put small amounts on to your float and rub the render into any dips or blemishes and then finally give the whole wall rub. I don't think you'll be pushed for time as its only a small area.

If you still want to skim after for any reason I would probably try out something like victas plaster, although I have never used that stuff myself

Render on fireplaces has a habit of cracking. Make sure you leave it a while before whacking the fire on. If it was me I'd add some fibres to the base coat or mesh it to give it extra strength.