I am in the process of repurpose my basement storeroom into a study room (size 3000mm x 3600mm). I have removed the old render and applied a waterproofing membrane to the walls as the original wall was damaged by rising damp (see below). I now like to render and paint the wall and like to seek recommendation on the followings: * To level the wall, I'd plan to apply cement render over the waterproof membrane so it can be made smooth for painting. Like to know what type of render can I apply over a waterproof membrane. * Is there a need to apply a primer over the waterproof membrane to improve the adhesion of the render? If so, what primer should I be using? * As the wall was very rough and uneven (i.e. there are areas which are off by ~30mm), I'd think it needs a two or more coats of render to make it level/smooth. In this case, should I be using a different render for the base coat and the finish coat? Appreciate for your advice. Cheers, Eric

How to render a basement study brick wall?

I am in the process of repurpose my basement storeroom into a study room (size 3000mm x 3600mm). I have removed the old render and applied a waterproofing membrane to the walls as the original wall was damaged by rising damp (see below).

Screenshot 2025-08-11 050119.png

I now like to render and paint the wall and like to seek recommendation on the followings:

To level the wall, I'd plan to apply cement render over the waterproof membrane so it can be made smooth for painting. Like to know what type of render can I apply over a waterproof membrane.
Is there a need to apply a primer over the waterproof membrane to improve the adhesion of the render? If so, what primer should I be using?
As the wall was very rough and uneven (i.e. there are areas which are off by ~30mm), I'd think it needs a two or more coats of render to make it level/smooth. In this case, should I be using a different render for the base coat and the finish coat?

Appreciate for your advice.

Cheers,

Eric

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EricL

Hello @eric_chan

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your basement project.

Can you please let us know what exact brand and model of waterproofing you used on your wall? If it is a Bunnings product, we'll be able to ask our supplier about the proper procedure in regards to rendering its surface. However, if it is not a Bunnings product, I recommend speaking to the waterproofing manufacturer about directions on how to render its surface. By providing us with this information we'll be able to answer the other two questions you have posted.

If you have any other questions we can help with, please let us know.

Eric

eric_chan

Thanks Eric. The waterproof membrane was applied by the professional Waterproofer several months ago. I only got time now to finish the basement into a study room. From memory, I believe the waterproof membrane he used is either Crommelin Cemproof Flex 1P or Sika 10kg Sikalastic Waterproof Membrane.

Regards,

Eric

EricL

Hello @eric_chan

Thank you for that information. We'll contact our suppliers and try to get more information from them in regards to rendering over the surface. As soon as we have more information, we'll get back to you.

Thank you for your patience.

Eric

EricL

Hello @eric_chan

I've just been in contact with Crommelin and Sika technical. Crommelin advises to download the Cemproof Flex data sheet 1P and refer to page three in regards to rendering procedures. They also advise using the Crommelin 15L 100% Acrylic Cement Modifier as primer and additive to your render mix. Please follow mixing instructions indicated on the container.

Sika has mentioned that if you used the Sika 1K Sikalastic you can render on to its surface directly. However if you used a different model please let me know as there are over 15 types of waterproofing membrane and they all have different rendering procedures.

If you need further assistance, please let us know.

Eric

eric_chan

Thanks Eric for the info provided. I’ll confirm with the waterproofer on the system he used and follow the instructions given to continue my rendering work.

cheers,

Eric

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