Easy DIY guide to fixing cracks in the home




Hairline cracks are common in walls in many homes but can be unsightly in a beautifully decorated room. However, cracks can also be evidence of something far more serious. Here’s how to tell for sure and what action you should take.


Hairline cracks in walls

There’s no need to worry about these. Hairline cracks are caused by movement and are very common in new homes recently plastered that are still settling as the building dries out. Even in an older home small cracks may appear due to ground movement.

The recent earthquake in the Orkney area was felt around South Africa as far away as the Northern Cape. These quakes might be minor when compared to earthquakes globally, but they are an indication that the ground beneath our homes is constantly moving.

The easiest way to deal with hairline cracks in walls is to use an interior crack filler, such as those in the Polycell range available at your local hardware store. But cracks around window frame and doors that constantly re-appear may need a more flexible type of filler to prevent re-occurrence and you will find products such as Pattex Acrylic Sealant convenient for these areas.


When filling hairlines cracks the trick is to enlarge the crack slightly around the edges so that the crack filler easily fills the gap and adheres to it. You can use a paint scraper or screwdriver to enlarge the crack to make it easier to apply crack filler and scrape away any excess.



  • When applying crack filler it is better to apply in thin layers of no more than 10mm thick and allow each layer to dry before applying another layer.
  • Use a paint scraper to fill in cracks up to the level of the surrounding wall to prevent excessive sanding of the area to finish off.




Hairline cracks where walls meet in corners

As with cracks in walls, these can be caused by drying out or movement. Cracks generally seek the line of least resistance and corners can be prone to cracks that occur repeatedly. Where cracks in corners have been treated with crack filler over a period of time, without success, a flexible crack sealer will fill up these areas and allow for a certain amount of movement. Acrylic fillers can be painted over in the same way as cement-based crack fillers but cannot be sanded, so ensure a smooth finish with a profiler kit or your finger tip before the acrylic filler has time to dry.


Cracks where plaster comes away from the wall

Where cracks appear and small pieces of plaster fall away this could be caused by poor application at the start, poor plaster mix, or be caused by damp in the walls. If you gently tap the wall around the crack and it sounds hollow, this could be an indication that the plaster coat is failing.

Areas of loose plaster need to be removed and replaced and depending upon the severity of the repair, you can look at doing a small job yourself using a product such as Polycell Masonry Patching Plaster or similar, or call in a professional plasterer.




ABOVE: On exterior walls use a hammer and chisel to widen out small and medium cracks to remove loose surrounding plaster.


Large horizontal cracks in corners or radiating out from windows or doors

Larger cracks in these areas could be due to ground movement or movement of frames and doors, especially where wood window and door frames are fitted. The wood frames themselves constantly expand and contract, causing movement to be passed into the surrounding plaster.

However, where these cracks appear on both interior and exterior walls this could be an indicating of a more severe problem cause by subsidence door to poor ground soil or damage to the foundation caused by tree roots. If in any doubt consult a structural engineer to investigate the problem.




Large vertical or stepped cracks in brick walls

Generally caused by subsidence or a fault in the foundation, cracks of this nature need to be inspected by a structural engineer to determine the cause. It may be necessary to add underpinning to the foundations, so do not attempt to repair until an inspection has been performed and a solution recommended.


If in any doubt, or if you have any concerns about cracks in your home, consult with a professional construction company that deals with home repair, or call in a structural engineer.

Janice Anderssen



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