Old random rubble built stone fireplace.
I want to render it (plaster will I think struggle with stove heat?) then paint it.
So how to prep the sooty old stone for best adhesion of the render?
What mix for the render?
What paint?
TIA
Jim K
Will you have a heat source (eg stove) in there?
If so, here's what I did with a brick fireplace:
Wire brush the surface of soot.
Paint on a slurry of white cement (eg Snocrete) to aid adhesion.
Apply render of snocrete/lime/silversand (play sand).
This gets a very light render. Then paint with a genuine lime wash (which you make yourself using the same lime you bought for the render).
That's heatproof and white in final finish.
Cement on stone is not best practice. Sometimes when it comes off years later it pulls a layer of the stone off with it. And there are other downsides. Lime mortar would be better, 3:1 sand & lime.
Basic lime paint doesn't mind heat. Mix builder's lime with water to make a putty, dilute 50/50 and paint on thinnish. It looks far too thin at first but isnt, it bodies up twice after painting.
NT
Oh dear, Mrs Lime Mortar strikes again.
I wonder why the industry abandoned lime as soon as Portland cement became available?
I'm not a Mrs.
Portland sets much quicker, so new builds can progress faster.
NT
/Tim Watts
- show quoted text - Will you have a heat source (eg stove) in there?
If so, here's what I did with a brick fireplace:
Wire brush the surface of soot.
Paint on a slurry of white cement (eg Snocrete) to aid adhesion.
Apply render of snocrete/lime/silversand (play sand).
This gets a very light render. Then paint with a genuine lime wash (which you make yourself using the same lime you bought for the render).
That's heatproof and white in final finish/q
Yes there'll be a stove there after.
What was the mix ratio for the render?
Cheers Jim K
/ snipped-for-privacy@care2.com
- show quoted text - Cement on stone is not best practice. Sometimes when it comes off years later it pulls a layer of the stone off with it. And there are other downsides. Lime mortar would be better, 3:1 sand & lime.
Basic lime paint doesn't mind heat. Mix builder's lime with water to make a putty, dilute 50/50 and paint on thinnish. It looks far too thin at first but isnt, it bodies up twice after painting.
NT /q
In this instance losing the top surface would not be a bad thing.
How long does lime render take to set?
I've used bog standard masonry paint before without issues..
Jim K
1:1:6 IIRC - (Cement:lime:sand)
The cement slurry to paint on first will just be a mix of cement/water to a honey like consistency.
Snowcrete is expensive, but it's worth it to get a very light mix, as is some "play sand" (easiest way IME to buy a small amount of silver sand).
Unless of course you are not going for a white finish, in which case use normal render ingredients :)
1:1:6 with cement will set in the usual short time (hours/day).
The lime is there to make it more plastic and less likely to crack when it gets hot.
It's now a good couple of years since our woodburner was put in. We've been told to use ordinary emulsion on the cement (?) finish behind the stove. We'll see.
Ordinary emulsion seems OK here after a couple of winters. The wall only gets warm, not hot.
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