How do I repair heavily broken wall plaster caused by a water leak?

[dinefera]

 

One of room wall was heavily damaged due to a water leak in adjacent bathroom. Though leak has been fixed, now wall plaster heavily chipped and broken. How to fix this plaster and bring it to normal wall appearance?

[dinefera]

So i went to Bunnings to seek advice. The guy told me to use Dunlop joint and patch render first and then apply pro rapid waterproofing acrylic membrane. But im not sure that i should render first and then apply membrane or other way around. And am i using right product?

[MitchellMc]

Welcome to the Bunnings Workshop community @dinefera. It's terrific to have you join us, and many thanks for your question about repairing a wall.

Hardwall plaster was likely originally used on the wall. It's similar to the Dunlop render, but it has a finer consistency and is easier to sand back to a smooth surface.

Provided the leak has been resolved and the wall has dried out, I see no need to use a waterproofing membrane on the wall, whether under or over the plaster.

Here's a helpful step-by-step guide: How to white set internal render.

Please let me know if you have any questions.

Mitchell
 

[dinefera]

Hi MitchellMC,

Thanks for helping out. If i still need to use waterproofing membrane, do i need to use before or after rendering?

[MitchellMc]

It's not advisable to use a waterproofing membrane as the Hardwall Plaster should be applied directly over the cement wall @dinefera.

It's counterintuitive to add a waterproofing membrane on this side of the wall. If moisture is coming through the wall, a waterproofing membrane would prevent that. However, that means there's an active leak, and adding a membrane would trap moisture within the wall, leading to structural damage. Membranes go on the side of the wall where water is to prevent it from entering the wall in the first place. So, you need to work out where the membrane has failed on the bathroom side.

Resolving leaks before performing repairs is essential. Trapping moisture in the wall with a membrane is a band-aid solution that will lead to very expensive repairs down the line.

Once you've applied the Hardwall plaster, you could use Aquablock as a primer before paint, but once again, that would mean there's moisture in the wall, and that's something you need to address separately.

Mitchell