hi
I would like to repair the fill the crack on my concrete boundry wall
is there any render which can be filled the crack and also as surface render ?
Welcome to the Bunnings Workshop community @Bossyboy. It's wonderful to have you join us and many thanks for your question on filling a crack.
That’s a fairly wide crack, so it’s not something you can just skim over with a bit of render and hope for the best. You’ll need to clean it out properly first and then pack it with a foam backing rod, pushing the rod down so it sits about 10mm below the surface. That stops you from filling the entire depth with product and helps the repair perform properly.
After that, you’ve got two options. You can use a cement-based filler or repair mortar and then skim it to match the surrounding surface. That will look good initially, but if the wall is still moving at all, there’s a good chance it will crack again fairly quickly. Boundary walls often move slightly due to ground conditions or temperature changes.
The better option, especially if there’s any ongoing movement, is to use Sikaflex 11FC in white. It’s a flexible polyurethane sealant, so it can handle movement without splitting. You would still use the foam backing rod first, then apply the Sikaflex over it and tool it smooth so it sits flush with the wall surface. That’s more likely to last.
If you’re unsure on prep and finishing, have a look at a guide on How to repair render.
Please let me know if you have any questions.
Mitchell
thanks Mitchell, I have some questions and hope you can help me further:
Bossyboy: question: So what is the size of the foam backing road that I should buy based on crack size? For example, crack is 10mm…
Bossyboy: So, will this kind of mortar look better and more match to surrounding surface than using the Sikaflex 11FC in white if no further crack or movement?
If we use the Sikaflex 11FC, is this also paintable as the cement- based filler or repair mortar?
Hi @Bossyboy,
You'd typically purchase the next size thicker than the crack. That would be the 15mm version. It then compresses and you push it into the crack.
Yes, you would get a better match using the mortar. Sikaflex is paintable and painting over it will help disguise it, but you'll likely still see the difference.
