What is slab jacking?

If your concrete is sinking, chances are the concrete floor was installed on a poorly compacted base. However, in the case of the Canterbury Earthquakes, it is possible that a void has been created under the slab. So how do we fix those voids?

Slabjacking is a process of either raising concrete slabs on-grade or filling voids underneath these slabs. It is undertaken by injecting Terrier Thixotropic 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 slabjacking 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 jacking. Terrier grout has been designed to maintain support for slabs in seismic situations where liquefaction may cause deterioration issues.

When is it appropriate to use this method? 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 slabjacking several times.

For further information on slab jacking, please contact Reid on 0800 88 22 12 or view technical information on our website.

Contact details for Stake Consulting, Christrchurch Approved Agent.