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I've taken a 3x3m first floor room back to bare brick, a lot of the old render could be tapped off so I've got 90% of the old off apart from the few really firm areas which I think are not original and had been patched up at one time.
I'm putting 50mm insulation directly over the top, probably 30mm thick held between battens with 20mm over the top of the battens held by screw, over this BC has said to put damp proof membrane sheet, then PB before skimming.
Question is, does it matter at all how I finish the render? leave it scratched or float it smooth?
I had thought to leave it scratched as if someone were ever to come in and want need to dot dab the insulation to the wall it'd adhere better, I'll be long gone by then and scratch is also less work
First time I've done rendered though, I've basically just held the hawk against the wall and pushed it into the brick, not played about with it too much and ruled it off horizontally / vertically, there's a few bows in of about 5mm or so in places so overall I'm pretty happy with it.
Struggling to picture what it is you're doing, are you talking about the inside or outside face of the wall?
If these are internal walls I'm not sure why you've put anything on them before the insulation.
And why render internally?
Leave it as laid but maybe dont sponge it in to fimish it off.
You did sponge it im didn't you?
There will be enough stiction on a std render mix for thistle first coat to stick to.
I am not a plasterer but can render and am teaching myself to plaster to an acceptable finish.
Inside face of wall, it was rendered previously and skimmed but a lot of the old render was coming away (its an old terrace)
Building Control where involved as took a chimney breast down, it did seem a bit pointless but they wanted it re-rendered before insulating
bit more detail, I'd bricked up the old chimney to the left of the batten.
You are right to provide a flat wall surface to then mount insulation. You don't want cavities which could gather damp.
Do look at things such as Pavatex or Heraklith which can be plastered straight onto. No need for plasterboard, struts or similar.
If you do go down the foam and plasterboard route, I believe you can just tape the joints on many foil faced boards so then don't need vapour control barrier.
Have you had interstitial condensation calculations done?
Thanks Matt, that was my thought on the cavities, the render does have integral water proofer in the mix which should help water entry, the room isn't particularly damp but will be a bathroom so always a risk.
Its 3m across / 2.4m tall, I've straightened it out to within 10mm across the face so I'm hoping this should reduce the cavity issue, but it's not perfect, issue I'm having is I'm only making a bag of sand mix at a time as it's all I can get up the stairs so is a bit patchy.
Scratch does mean there is also small cavities which was another reason for the leave scratched or no scratch question.
We didn't do scratches behind Pavatex when installing that.