STAINED NEW LIME PLASTER

I took the up the cause and have started to replaster my exposed brick fire place in lime plaster, but as it has been drying over the last few days a nasty brown stain has soaked through from the brick work. I suspect it is tar from inside the flue going through the original lime mortar when i have dampened the bricks prior the plastering - is this true? and how should i hide this? I have only put the first coat on of about 1/2 inch. Is PVA a good idea or not?

I have always managed to avoid having this problem by not plastering in such locations. So, I can only tell you what I have been told and it's not very pleasant!!!
It is said that good ole cow#####is the answer.
Knock it up 50/50 with your lime plaster and paste it on. Or apply neat. I can't remember.
Apparently it will hold back the staining and cease to be smelly once dry. And no, I am not winding you up!
If you choose to give it a try I would be fascinated to hear whether it is successful.
No, I would not use PVA on principal and I am pretty sure it would not work.
If it is only an isolated area and you are prepared to sacrifice breathability you could try Styptic (from your decorators merchant). This will hold back bitumen paint so I would have thought it would work. Mike.

Cow dung is the traditional solution - although, no. I haven't tried it either!

I'm not sure how breathable a chimney breast has to be really. The lime will look much better than gypsum though. PVA I'd certainly avoid, and I'm not sure it will work either.

I heard daub worked but not tried it myself.

Cow#####*is* the answer - I've tried it and it works. For best results, use the stuff as fresh as possible; the old maxim is you get it before it hits the ground!
Mix it to a thickish slurry with water and paint on two coats, allowing each to dry. Then mix fresh dung with the scratch coat on a 1:1 ration with your lime putty and apply 1cm thick. You'll prevent all soot and tar staining that way.
It *does* smell, but the smell grows on you and will go after a week or so.

Exellent Gervase, I always wondered whether it worked.
Did you mean 1:1 lime putty:cow#####as stated, or did you mean 1:1 lime plaster:cow shit?
Any ideas why it works? Mike.

I've done it with 1:1 cow dung and putty, with slightly less sand - two parts of sand to each unpleasant bucket-load of putty/dung mix.
As to why it works, I'm not sure, but there's a fair amount of mucous in cow dung which must form some sort of layer as it dries which is still breathable and water-permeable but resists the transfer of the oily tar molecules.
In the last century and before, nearly all chimneys were parged with dung (as is still the practice in the developing world) and it seems have stood the test of time. Trouble is, once the parging has broken down, it's a beggar to replace unless you rebuild the chimney, so a modern liner is the only real alternative if you've got a leaky flue. Maybe there's some way of spraying it inside the flue, but I haven't come across it - and the prospect of teaching cows to squat on top of the chimneys doesn't bear thinking about!

Scaffolding, jenny wheel and a strong rope mate, done it loads of times.
Thanks for that, I am looking forward to the chance of trying this one day. What a great bit of bullshit (pun intended)!
I can just see myself with the client now -
'Cor bugger, us can sort thiggy. Great Granfer showdus, an is Granfer showdee .... etc. etc.' Mike.

...and PVA most certainly doesn't work, as I found out only yesterday. A decorator was brought in to tart up an unfinished old hearth in our place for a photo-shoot over the weekend and was asked to slap a coat of limewash over some newly repointed stonework which had a lot of tar and soot leaching through/ "No worries, I'll put some PVA on and you scratch it off later with a wire brush when you do your plastering; that'll stop any staining" he said. He ladled great dollops of the bloody stuff on the wall and, sure enough, the staining came straight through.

I think I'll stop eating my lunch while I read these posts!!