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.
thanks Mi
sorry for some more questions
I would like to use some ready for use render to cover the crack..
mmy questions are
1. what kind of "ready to use" (premixed) render do you recommended do such kind of concrete wall where it has been rendered and painted before.. my aims is to fill the crack with render and then paint it over
2. do I need to put primer (like concrete sealer) on the existing wall before I put the new render? any recommended products?
many thanks
Hello @Bossyboy
If you are after a ready to use render, I suggest looking at the Dunlop 16kg Ready To Go Premix Render. It is a white, ready mixed render suitable for indoor and outdoor projects over a wide variety of surfaces including brickwork, AAC blocks, fibre-cement sheet, painted surfaces and concrete. Please remember that you will still need to use the foam backing rod on your wall.
I propose looking at using the Dunlop 1L Multipurpose Water Based Primer on the inside and outside of the gap. This will prime the surface and promote adhesion.
If you need further assistance, please let us know.
Eric
thanks Eric
Dunlop 16kg Ready To Go Premix Render look very good and suitable
but I look at the product size which is 16kg? do we have some smaller size as I worried I cannot use at once and just waste
The Dunlop 16kg Ready To Go Premix Render does not come in a smaller container. My only other suggestion is to use the originally suggested products which are the cement-based filler or repair mortar.
Thanks Eric, I checked and found this one…is it do the same job for this kind of crack repair?
Selleys 440g Off White No More Gaps Bricks And Mortar Gap Filler - Bunnings Australia
just look at something easy to apply and less messy…, i am a beginning of DIY : )
Yes, that would work, but you would need a few tubes of it. I'd say two or three should do the trick.
Let me know if you have any further questions.
Jacob
hello bunning
thanl you so much for all your advice before
I found this product and would this also do the job by filling the crack on mansory wall?
do we need primer before putting this?
sorry forgot to post the product I mentioned
https://www.bunnings.com.au/selleys-180g-spakfilla-rapid-gap-filler-180g_p1231864
My advice would still be to use the Dunlop 5kg Ardit Rapidset Repair Mortar I recommended in my first reply. It's specifically designed for the job you have, and it is the most likely to give you the best and longest-lasting results. It's also the smallest quantity of a professional-grade product we have. Products like Selleys 180g Spakfilla Rapid Gap Filler are soft DIY products, which are not designed for this purpose and really should only be used for small cracks or missing sections. You have a very wide structural crack, and although you could use the Selleys product, it is not the most suitable, and it will probably fail in a short amount of time due to this.
thank you
I may probably try the Sikaflex 11FC in white as recommended initially to fill the crack and painted it over
however, what kind of paint will be best to paint over this kind of polyurethane and my mansory wall so the paint can be best stick to both materials?
Water Based or solvent bases paint?
do I need primer on the sealant and my masonry wall (the wall was rendered and painted before)
No primer is required @Bossyboy, and I'd suggest using a water-based Dulux Weathershield.
hello
thanks
i want to confirm one thing
i checked the instruction of the silika white 11 FC
it said it need to apply the below primer on the concrete if using it to fill the concrete crack.
Sika® Primer-3 N
so do I need the primer on the concrete crack before applying the silika white 11FC?
Do you need Sika Primer-3N? Yes, it is the best practice for exterior concrete, as it guarantees the manufacturer’s stated performance, ensures a weatherproof seal, and acts as an adhesion promoter. Can I use the Sika 11 FC direct without the primer? Yes, it can be used direct on clean, dry concrete, but for high-performance, long-term exterior applications, use of the primer is advised. If you skip the primer, make sure the concrete is perfectly clean, dry, and free of dust. The sealant must be firmly tooled into the crack.
