3 Different Wall Cracks and How To Fix Them

Repair a Wall

If you want to fix cracks on your wall, the most important thing you must determine is what is causing the crack in the first place. The three types of cracks on a plastered wall are:

  • Hairline cracks
  • Cracks caused by water ingress
  • Structural cracks.

    Let’s look at the difference between these types of cracks: how to identify them, how they are caused, and how to fix them.

  • Hairline Cracks

    Hairline Crack

    Hairline cracks are most commonly found on newly built or freshly plastered walls. This especially happens if there was some shrinkage in the mortar because the plaster dried too quickly. To fix this, you need a high-quality product that will stop moisture from getting into the cracks, and to flex with the cracks, if necessary.

    Elegance has an elongation of 200%, and applying two coats can fix those hairline cracks.

    Hairline cracks also include settling cracks, which are cracks that appear approximately 2 years after a wall is built. If these cracks are not wider than 3mm, fill it with Flashpatch Exterior. If settling reoccurs and gets much worse, the problem could be caused by expansive soil at the foundation, and you may need to ask for professional help.

    Water Ingress

    Water Ingress

    If there is moisture in a wall, it will start evaporating when it gets warmed up by the sun, and so the moisture will try to escape from the wall. It will either do so through small, existing cracks, or it will push through and create new cracks.

    The first thing to do is repair the area that is leading so much moisture into the wall. The problem is normally around flat areas like parapet walls and windowsills, especially where there are existing cracks, holes or unpainted areas where water can seep into. You may need a good waterproofing solution.

    To repair this kind of crack, scrape the raised crack open and check for signs of algae, like in the picture below. Kill the algae with a biocidal wash and allow enough time to dry before sealing the crack. Once the sealer is dry, you can apply Flashkim Interior or Flashpatch exterior. Remember to skim Flashpatch exterior as smoothly as possible while it is still damp, as the surface dries very hard.

    Structural Cracks

    Structural Cracks

    These cracks are caused by structural movement and will keep reoccurring.

    Structural cracks are repaired by cutting expansion joints into the plaster which will allow for movement. The expansion joints are filled with a very flexible sealant that will move inside the joint. These joints are usually found along concrete slabs that expand and contract at different rates, or along joints on freestanding wall. If the joints are not properly built in during construction, then structural cracks will occur. It would be best to seek the advice of an engineer or building professional who could give a recommendation on where the joints should be cut.


    1. Robin Matthews says:

      I need some advice on fixing structural cracks. I am based in Cape Town. Can someone assist?

    2. mamosebo charles says:

      good day I need a quatation

    3. Tersia Visser says:

      It would be appreciated if you could assist with contact details of building professionals that can assist with the repair of structural cracks.

      Thank you

    4. Starbright says:

      Hi Matthew, you can contact our Wester Cape branch in Milnerton City on 021 555 1995.

    5. Starbright says:

      Hi Mamosebo, you can contact our head office for a quote on 011 794 2885.

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