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How to fix cracks in render to prevent water damage or mould?

I recently noticed these greenish marks on the render around my house, and was worried it may be mould from water coming in through the cracks. What is the best way to prevent any mould forming or it getting worse? I was going to apply a coat or two of paint to help fill in the cracks but wasn’t sure if this would keep water out and make a water-tight seal or if it’s better to use a gap filler. Or would that make the problem worse if the area can’t breathe and dry out properly if there’s existing water damage?

Any assistance you could provide would be greatly appreciated.

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Comments

Jason

Hi @amethyst83,

Welcome to the Bunnings Workshop community. We're pleased to have you join us.

Experienced member @Nailbag recently shared a step-by-step guide How to repair a rendered wall. It would be great to get his opinion on whether these are substantial-enough cracks worth addressing or whether simply cleaning might be the best approach.

Our resident Bunnings D.I.Y. experts will also be happy to assist with their opinion as soon as possible.

Feel free to post anytime you need a hand with a project around the home or garden. We're here to help.

Jason

MitchellMc

Hi @amethyst83,

How long ago was this rendering done? It appears to be compromised, cracked, and failing. When we render on the front of a wall and paint it, we effectively seal moisture in. If we haven't waterproofed the rear side of the wall, then the moisture from behind can't go anywhere and will blow the paint off the wall or cause the render to fail.

In this case, you could apply paint to the area to temporarily disguise the issue. You might get a couple of years out of that.

Your best bet might be to have someone install some furring channels on the wall to create an airgap and then screw fibre-cement sheeting over and paint that. You'd still have the rendered look, but the sheet will be de-coupled from the wall and not affected by the moisture from behind.

As these are hairline cracks, there's no easy way to fix them, and even if you did, the render is likely to continue cracking. To repair the cracks, you'd need to chase them all out and open them up before filling them. There are just too many there for that to be a viable option.

Please let me know if you have any questions.

Mitchell

amethyst83

https://www.workshop.bunnings.com.au/discussion/comment/43241#Comment_43241

Thanks Mitchell for your advice here. The tender was done about 9 years ago when the house was first built. I’ve noticed a few others in this area that look similar with the hairline cracks on the tender. So does it seem like the rear side of the wall hasn’t been waterproofed like it should have been?

Regarding the option to install some furring channels on the wall and screwing fibre-cement sheeting over that - what type of tradesperson would do that work? Like a plasterer or general handyman? Just not sure where to start asking for quotes etc

amethyst83

https://www.workshop.bunnings.com.au/discussion/comment/43181#Comment_43181

Thanks Jason! @Nailbag that would be great if you had any additional input to provide here 😊

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/83736#Comment_83736

It's a bit hard to tell @amethyst83.

I think the darkening of the cracks is certainly an indicator that moisture is present in the wall and that could mean it wasn't sealed. However, I would not be surprised seeing this type of cracking on a nine-year-old wall that was sealed.

At this stage, I'd probably just apply a couple coats of a quality exterior paint and see how you go.

For that type of work, a general handyperson would be needed.

Mitchell

Nailbag

https://www.workshop.bunnings.com.au/discussion/comment/83736#Comment_83736

Hi @amethyst83

I would agree with the comment @MitchellMc has made and would start by taking his more simpler approach and repaint the area. It could be the result of a thin area of render poorly prepared, thus being a more cosmetic issue. If you wanted a more structural repair, then a renderer would be the best trade to contact.

Nailbag

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