Foundation Repairs

The Problem with Sinking Foundations

If the foundation soil on which a concrete slab or footing is built contains degradable material, has been subject to erosion, heavy loading, vibration, or was not adequately compacted at the time of construction, there is a likelihood that over time these soils will subside. As the foundation soil loses volume and sinks, the concrete above is deprived of support and will develop voids beneath and/or drop.

If left untreated, sinking foundations can lead to a number of issues of concern which include:

  • Trip hazards,
  • Reduced asset value and rentability/saleability,
  • On going deterioration,
  • Reduced operational performance.

Indicators of Sinking Foundations

Sinking rarely affects foundation soils uniformly, resulting in distortion of the structure caused by the difference in movement. Common indicators include:

Exterior Indicators

  • Diagonal cracks through concrete and stair-step cracks through the mortar beds of brick and block walls. These cracks often begin at the corner of a door or window, and typically, these cracks will be wider at the top than the bottom.
  • Walls that are out of alignment.
  • Opening of articulation joints. Sections of wall are often constructed with vertical joints to allow for thermal expansion and contraction. Any permanent change in these joints can often indicate sinking.
  • Opening of joints in the roofline facia and soffit.
  • Uneven joints around doors and windows. Doors and windows may start to stick or open/close on their own and glass can be caused to break.

Interior Indicators

  • Cracks in interior walls, cornice, and ceilings. As with exterior cracks, these will often begin at the corner of doors and windows, but they are also common at joints in the plaster.
  • Cracks in brittle wall and floor finishes.
  • Gaps between the floor and skirting boards.
  • Opening of carpentry joints and cupboard and door frames that are out of alignment.

Slab Indicators

  • Adjacent slabs are visibly out of alignment, have low or high points, or voids are evident beneath the slab edges.
  • Slabs move at joints or pump out water when traffic moves over.
  • Slabs sound hollow, bounce, or transfer vibration.
  • Sections of concrete are breaking away at corners or joints.
  • Surface water no longer runs off as it was intended to.
  • Significant cracking. These cracks often run parallel to areas of subsidence.

Whilst the above are all indicators that your foundation soils may be subsiding, there are other possible causes of structural movement and these should be investigated. If you think that your property is being affected by sinking foundations SlabJacker recommends that you consult a structural engineer. A structural engineer will not only be able to diagnose the problem, but should be able to identify contributing factors and can work with SlabJacker to plan a programme of repair.

SlabJacker’s Solutions to Falling Foundations:

  • Slab Jacking
  • Rocking Slab Stabilisation
  • Chemical Underpinning and Piles



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