Slab Jacking with Reids

Void filling and structure relevelling are the newest services from Reid using Terrier Thxiotropic Grout.

Also known as Slab jacking, it is a process of either raising concrete slabs on-ongrade or filling voids underneath these slabs.  It is undertaken by injecting thixotrpic grout under pressure into the void below the slab.

Reid’s Terrier Thixotropic Grout has been specially developed for this application and  overcomes the problems commonly encountered with normal void filling methods. The Thixotropic Grout is viscous enough not to leak into fissures or cracks in the ground and to reach a compressive strength of approximately 25MPa after two hours. This prevents slabs settling back from their desired level after relevelling.

Terrier grout has been designed to maintain support for slabs in seismic situations  here liquefaction may cause deterioration issues.

Slab jacking diagram


The method is used when a concrete slab has settled or lost support for various  reasons, such as:

  • weak sub-grade material,
  • improper compaction of sub-base,
  • liquefaction of sub-grade,
  • erosion of the sub-base,
  • shrinkage of the sub-grade

Slab jacking can be used to re-level the slab and to re-compact sub-grade and sub-base material to some extent but cannot be relied upon to completely rectify underlying poor soil conditions.

Sometimes the raising of a slab may be difficult due to the binding of the slab at the cracked sections. If soil settlement continues, it may be necessary to repeat the this method several times.

The method of structure re-levelling will depend on the following conditions:

TYPE 1: Where the slab has cracked and dropped but is still supported by the sub-base material.  Settlement in these slabs is readily identifiable by the presence of cracks in the slab.

TYPE 2: Where the slab has not cracked but has lost support from the sub-base material and is spanning a void beneath the slab. Identification of this problem is evidenced by settlement of slabs or bouncing of slabs under loads. Verification of the extent of the problem is undertaken with NDT testing whereby the void detection is undertaken with a ground penetrating radar. This investigation can be undertaken by Reid Applicators.

For further information on this service, download the technical data sheet from the Reid resource section. You will need to log on to access this document.

Our Christchurch partner Stake Consulting is available to undertake ground radar detection and provide a full void filling and structure re-levelling service.

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Stake Consulting, Unit 5/7 Burdale Street, Riccarton, Christchurch

ph: +64 3 3480 292    e: