How to repair rendered walls before painting?

[hessian86]

 

Hi, I am repairing walls ahead of painting and in a few spots we have drummy render, which I have removed in this picture. I have a couple of questions:

1. The house is about 80 years old and the render on the brick crumbles like sand. Is this normal/any cause for concern, as the whole house would be affected. 
2. to replace the removed render, should I use a quick set mortar, or mix up acrylic render?
3. the render has a thin white coating on it, is this a plaster coat? And after patching the render, do I replicate this with a finishing plaster?

thanks

Christian  

[MitchellMc]

Hi @hessian86,

It's not unusual for older renders to become crumbly over time, especially in homes as old as yours. If the render starts falling off by itself, or if you're concerned about the extent of the damage, it may be worth having a professional assess the condition of the walls.

For filling the void, I'd recommend using an acrylic render rather than a quick-set mortar. Acrylic renders are more flexible and durable, making them a better option for older walls. Once the render has set, you can finish off with a Hardwall Plaster to replicate the thin white coating you're seeing.

Before applying the render, sand any paint around the damaged area back by about 15cm. This will help you feather the plaster out smoothly, avoiding a visible transition between the new and old surfaces. Once patched and dry, use a sealer binder primer before applying your paint topcoat.

Given the age of your home, there's a chance that asbestos could be present, particularly in older plaster, insulation, or building materials. Asbestos can cause serious health risks, including asbestosis, if disturbed. Before proceeding with any significant work, it might be a good idea to have the area checked by a professional for asbestos to ensure your safety.

For some extra tips, check out this helpful step-by-step guide: How to repair a rendered wall.

Let me know if you have any more questions or need further assistance.

Mitchell

[hessian86]

Thanks Mitchell. We had the wall previously tested for asbestos with nothing found. 

Is there any particular acrylic render you recommend, as there seem to be a few options?

When applying the render, do i apply it ~2mm shallower than the wall, to allow space for the plaster finish over the top?  

Regarding the sealer primer, do you mean a standard paint undercoat like Taubmans 3 in 1?

Thanks

Christian 

[MitchellMc]

Sorry, @hessian86, my link doesn't appear to have worked. I recommend Dunlop 20kg Multipurpose Acrylic Render.

That's it with the render. Apply so it finishes a couple of millimetres below the plaster so you can then skim over it.

I'm having an off day with my links. It's Dulux 1L PRECISION White Sealer Binder that I recommend, though it is a special order item. It's designed for porous surfaces like Hardwall Plaster, and it's technically what you should use. You could probably get away with a standard primer like the Taubmans 3-in-1.

Mitchell

[hessian86]

Thanks Mitchell, is this the plaster you were thinking about: Gyprock CSR 20kg Hardwall Plaster - Bunnings Australia

Does it need to be mixed with hydrated lime? I also read somewhere that I could skim with cornice cement, as it can be easier to work with and quick drying? 

[MitchellMc]

Hi @hessian86,

Yes, that is the product, and it is ready to use—just add water. There is no need to include lime. You could use cornice cement or topping compound, though cornice cement is not designed specifically for this purpose.

Mitchell