How do I repair this render block wall?

Hello, the previous owner just filled in wooden slatted cutouts of the tender wall with more blocks and Lo and behold it has cracked along the lines. As a total newbie, how can I repair this without it cracking anew every 2-3 years? If you don’t mind being as specific as possible with materials and tools that would be fantastic. Thank you very much!

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MitchellMc

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

Given that the previous owner filled in the timber slatted cutouts with blocks, and you're now seeing cracks along those lines, it's likely that there's movement in the wall, which is causing these cracks to appear.

One approach that might work better is to create an expansion joint where the crack is occurring. An expansion joint allows the wall to move slightly without cracking. This method does mean you'll have a visible line, but it could be a more durable solution over time.

Alternatively, if you're looking for something simpler, you could use a flexible filler instead of a cement-based product. Flexible fillers are designed to handle some movement, which gives them a better chance of staying intact without cracking or pulling away. However, this is more of a temporary fix and may not hold up as well in the long term.

In terms of materials and tools, for the expansion joint, you’ll need a grinder to create the cut, and then you'll insert a backer rod and sealant to finish it off. For the flexible filler option, you'll just need the filler itself and a caulking gun.

Additionally, it might be helpful to provide some more information on the timber slatted cutout. Understanding how these areas were constructed could give more insight into why the cracks are happening and what the best repair method would be. For instance, if the timber was used to accommodate movement in the first place, the block filling might be fighting against that natural movement, leading to cracks.

Please let me know if you have any questions.

Mitchell

gcl

https://www.workshop.bunnings.com.au/discussion/comment/40666#Comment_40666

Thank you Mitchell. The quick way sounds appealing. Can you still get the render finish using sikaflex? Should I v cut into the crack and try to fill it deeply? Sorry, again super newbie here just trying to give it a go! Any detailed advice would be so so appreciated!

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/82496#Comment_82496

You want to open the gap up slightly so the Sikaflex is caulked into it instead of just on the surface @gcl. A Craftright 5-in-1 Scraper or even a score and snap knife would be useful for this. If the cement is quite tough, then you might need to look towards mechanical means, like an angle grinder.

You'll be able to mimic the rendered surface to a certain degree. I'd take an old paintbrush and cut the bristles down so they are short. Allow the Sikaflex to cure for 10 minutes so it's not so sticky, and then come back and stipple over its surface with the brush. The idea is to pull little peaks up so it replicates the surrounding texture. You'll need to paint the wall to help the repair blend in adequately.

Mitchell

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