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How to fix a fibre cement crack at a join?

I'm hoping the community can assist with their experience. I have an external building clad in fibre cement (I assume to be blue board). It has been up for approximately 10 years and the wind/weather has caused one of the board joins to crack, letting in moisture. I am trying to determine the best process to fix and seal the crack. What is the best approach and materials needed? Thanks in advance for any advice.

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MitchellMc

Hi @Lawzy,

Could you tell us a little more about where this crack is located and how the water enters it? If it's on a verticle surface, you might get away with chipping out any deteriorated material and filling the crack with a repair cement like Dunlop 5kg Ardit Rapidset Repair Mortar. The product can be simply trowelled over and pushed into the crack and sanded back flush with the surface before re-painting.

If this is on a horizontal surface and water is pooling and entering the crack, then we'd need to look at a more permanent solution.

I'll be looking forward to hearing further details and assisting with any questions you have.

Mitchell

Lawzy

https://www.workshop.bunnings.com.au/discussion/comment/25160#Comment_25160

Thanks @MitchellMc

The image is a horizontal join on a vertical wall and exposed to the weather. Rain is seeping through and over time the internal frame is getting wet. I believe your solution lines up with the challenge and I'll give it a shot, thanks.

Chris.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/75241#Comment_75241

Goodluck, @Lawzy, and please shout out if you get stuck or need further assistance.

Mitchell

Lawzy

https://www.workshop.bunnings.com.au/discussion/comment/101355#Comment_101355

To wrap up this question, I removed the old and added new synthetic reinforcing tape, and sealed it with the rapid set mortar. That did the job nicely.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/118122#Comment_118122

Great solution, @Lawzy! Many thanks for getting back to us and letting us know the method you used.

Mitchell

Bel789

https://www.workshop.bunnings.com.au/discussion/comment/118122#Comment_118122

Hi @Lawzy,

I am facing exactly the same problem. Just wondering how your fix has held up? Thanks.

Lawzy

https://www.workshop.bunnings.com.au/discussion/comment/127920#Comment_127920

Hi @Bel789 and sorry for the delay. I ended up removing the old filler and gap tape from between the panels, relaying the tape and then filling it with Dunlop Joint and Patch. So far, all good. Getting the old material off was surprisingly easy once I got going.

DIYJT

https://www.workshop.bunnings.com.au/discussion/comment/25160#Comment_25160

Hi Mitchell

i have external rendered blue board cladding over top two levels front and side of three-storey townhouse.

They have:

- hairline vertical cracks in the render where the boards appear to be joined very close together (including at corners of the building where front and side cladding meet)

- horizontal gaps between boards which appear to be filled with some sort of flexible sealant which looks to have cracked (maybe some sort of expansion joint) - these joints are slightly recessed

- popped nails

They whole facade leaks like a sieve with water getting in behind the wall wrap (foil paper stuff) somewhere - potentially through:

- screws that fasten decorative aluminum channel strips to the facade, some of which are only into the blueboard); and/or

cuts/defects in the wrap application

Do you have any suggestions for how I might seal the vertical and horizontal cracks?

I was thinking your suggestion above for the vertical cracks and a flexible paintable sealant for the expansion joints but I’m not sure what product would be best. I’ve tried using Selleys roof and gutter silicone and their paint over sealant but both a hard to use and look crap. I was looking at Sellys Flexiseal Polyurethane Construction Sealant which I think is paintable but not sure about its moisture protection properties.

For the screw holes I am think about using silicone sealant along the aluminum channel strips to prevent water getting behind to the screws.

Any suggestions you have would be greatly appreciated!

Regards

joel

Akanksha

Hello @DIYJT,

My sincere apologies for the delay in responding to you. @MitchellMc has been away on a well-deserved break but our other resident Bunnings D.I.Y. expert @EricL will be happy to assist as soon as he can.

Let me also call upon our ever-helpful members @JoeAzza, @Jewelleryrescue and @Prof in case they have any thoughts.

Thanks for your patience in the meantime and my apologies once again.

Akanksha

DIYJT

https://www.workshop.bunnings.com.au/discussion/comment/33623#Comment_33623

Thanks!

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/79134#Comment_79134

Hi @DIYJT,

Sorry for the delay in my reply.

Can you provide some images of these cracks so our members have a better idea of what you're working with? Let me know if you need a hand uploading images.

From what you've explained, it sounds like you're past the point of bandaid solutions, such as filling the cracks with polyurethane or silicone. The cracks should be chased out, the degraded material removed and patched with a cement-based filler, and the nails should be driven back in and filled over. Once this is done and all other leak points are resolved, you can paint the wall to ensure it is water-resistant.

My suggestion would be to enlist the services of a professional to quote the work and find out exactly the extent of the issue. That would likely allow you to decide whether sealing the gaps with a caulked product would be feasible.

Please let me know if you have any questions.

Mitchell

DIYJT

https://www.workshop.bunnings.com.au/discussion/comment/103922#Comment_103922

Thanks Mitchell! I appreciate the advice! Definitely a professional is required.

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