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How to clean a concrete wall?

We has new tiles laid with new waterproofing. As you can see from the photos it looks like the waterproofing has leaked from under the tiles. It is very hard to get off even with a scraper as it is thickish in parts. I want to paint the wall and want to know what I can use to get the stuff off. Can anyone help please ? Thank you, Gail

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EricL

Hello @gailhc

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

Depending on the type of waterproofing that has been applied, its possible that the overflow hardened to full strength. Getting it off might require a grinder and a Josco 100mm Twistknot Cup Brush. My best advice is to test a small area first and not to overdo it to prevent damaging the concrete surface. Your goal is to remove the waterproofing stains and restore the original finish on the surface before painting it.

Let me call on our experienced members @Dave-1, @Nailbag and @AlanM52 for their recommendations.

Please remember to wear personal protection such as gloves, goggles and a mask when working on your project.

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

Eric

Nailbag

Hi @gailhc

Thats a terrible mess thats been left for you to clean up. That wire brush that @EricL suggested would be a possible solution to try but it will leave scouring marks within the surface as you're likely going to need to go reasonably deep to remove the stains. And take the advice on the PPE as fine strands of wire do on occasion fly off as it wears down.

Another solution is to simply cover it with cement sheet with a cutout around the vent. Then prime and paint. Then lightly use a 120G flap wheel to clean the vent veins up and respray them. You will need a sparky to disconnect and reconnect the round light.

Nailbag

Dave-1

Good Morning @gailhc

How high is the runoff over the concrete? I would have a go with a wire brush wheel first and then depending on the roughness that is left maybe a light grind with a grinder. Tho as @Nailbag has mentioned you could end up with scouring.

I have found the wire brush wheel with a powered drill works better then a battery drill.

Dave

gailhc

https://www.workshop.bunnings.com.au/discussion/comment/58619#Comment_58619

Dave-1, Thanks for your reply. I will try the wire brush. The run off is about a metre. Gail

gailhc

https://www.workshop.bunnings.com.au/discussion/comment/58616#Comment_58616

Thanks you for your suggestions. Gail

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