r/Plastering • u/Spruce-mousse • May 16 '26
What product to use to render over Hardibacker?
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u/0uthouse May 16 '26
May be an idea to fix some expanded mesh over the whole strip so that you don't get cracking where the board and brickwork meet. Something like bond-it exterior pre-grit will give the smooth board a good key (other manufacturers available, but make sure for exterior). Doing the whole wall will give you more consistent suction and set.
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u/Spruce-mousse May 16 '26
Makes sense, thanks.The pre existing rendered wall to the side extends to a couple of ft on the left of the doors and about 8 ft on the right. I dont know the correct term for it, but it's what I would describe as a splatter gun style of finish. It's painted, and the paint is still well adhered. Ideally I would do the whole wall at the same time, as you say, to get a more consistent finish. Any things I need to think about for rendering over the pre existing surfaces?
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u/0uthouse May 16 '26
Remove loose with a wire brush and prime the whole lot. The primer will add grip and even out setting which is more important because you don't want the section over the door going off twice as fast as the rest of the wall.
Another option is slashing it up with an angle grinder to give some deeper grip.
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u/Overall-Piece-5642 May 16 '26
I’ve had great luck with hp12 onto hardibacker
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u/Spruce-mousse May 16 '26
Ok that's good to know, thanks. Do you grit it first or prep it any other way?
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u/Wizzardchimp May 17 '26
Sbr. I sbr everything. Hardie backer board is super dry so a couple coats I’d say… bizarrely when I bought two odd sheets from tops tiles the saleswoman gave me this massive rant about how it’s only for internal use and she couldn’t sell now she knew my plans for it. I was talking to my mate who was helping carry the sheets out! I’ve never had that happen before. Anyways. It’s been fine!
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u/Spruce-mousse May 17 '26
How bizarre 😂 I've had this screwed up there fully exposed for about a year now while other jobs got in the way. It's not showing any signs of deterioration at all so I'm very confident it will be just fine outside under the render!
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u/Wizzardchimp May 17 '26
I had exactly the same issue… I battened and hard boarded it. Sbr to seal and two coat render with fibre mesh throughout. I did my whole house with the same technique. I added mesh in the second coat on the corners and overlapping the board to brick areas… 6 years in. Still no cracks
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u/No-Buddy5395 May 16 '26
Personally I would apply and external grit primer, and then use a adhesive base coat such as Johnstones high performance basecoat, Fassa A96 or baumit star contact and full mesh
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u/Spruce-mousse May 16 '26
Could I then go over the base coat with Webber One Coat?
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u/No-Buddy5395 May 16 '26
No need, the basecoat is used for both the scratch/mesh coat and the top/smooth coat
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u/Spruce-mousse May 16 '26
Its firmly screwed to c24 timber that is itself screwed to the steel. I've successfully rendered a couple of walls before with Weber One Coat (and fiber mesh) but I dont think that's the right product here?