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How to fix cracked exterior cement board , i preferred sort of plastering
Welcome to the Bunnings Workshop community @sijo. It's sensational to have you join us, and many thanks for your question about repairing cement board.
Before doing anything with cracked fibre cement board, it’s really important to consider the possibility of asbestos, especially if your home was built before the late 1990s. Many older fibre cement products used asbestos as a reinforcing material, so if the board hasn’t already been tested, I’d strongly recommend having it checked by a professional before starting any work. It’s not worth the health risks if there’s even a chance it might be asbestos-containing.
Once you’ve confirmed it’s safe to proceed and the board is asbestos-free, you can go ahead with repairs. If the cracked section is still firmly attached to the wall and hasn’t shifted or crumbled, you can patch over it rather than replace the entire sheet. For this, a cement-based exterior filler is ideal.
Start by giving the crack and the surrounding area a good clean to remove any loose material, dust, or paint. If the edges of the crack are slightly raised, lightly sand or shave them back to create a flush surface. Apply the filler in layers using a broad knife, pressing it into the crack and feathering the edges out to blend it into the surrounding board. Once dry, give it a light sand, seal it with a suitable exterior primer, and finish with exterior-grade paint to protect the patch.
Remember your PPE, including a face mask and safety glasses.
Please let me know if you have any questions.
Mitchell
