Slabjacking is a specialty concrete repair technology. In essence, slabjacking is used to lift a sunken concrete slab by pumping a substance through the concrete, effectively pushing it back up from below. The four types have the similarity of injection of materials through slab but dissimilarity of material type being pumped
- Sand Jacking
- Lime stone Jacking
- Poly Urethane foam jacking
Depending on the result to be achieved and the sub-slab soil type will determine the most appropriate selection of material to be used. The first 3 methods have cement in the material mixture making them a cementious grout. Each material has it’s pro’s and con’s
Typically this process is used to relevel sunken slabs and keep them in a stabilized position.
The actual causation of settlement is due to a wide variety of factors one of which is soil moisture inconsistency. Soil expands and contracts as the levels of moisture fluctuate during the dry and wet seasons. Soil erosion also contributes to concrete settlement, which is common for locations with incorrect drainage. Houses built on land fill will typically settle more. Poorly designed sidewalk or patio slabs direct water towards the foundations level of a structure. Along with tree roots sucking moisture out and heaving slabs up
After determining the causation of the slabs movement and rectifying the cause one then selects the most appropriate type of slab jacking to return its profile.
The advantages of slab jacking as opposed to demolition and rebuild are:
- Cost – can be significantly less expensive than new concrete and reinforcement.
- Timeliness of the repair – concrete is typically usable within hours as opposed to days with new concrete
- Minimal or no environmental impact – mostly due to keeping waste out of landfills
- Aesthetic – does not disturb the surrounding area and landscaping which would have to be re- landscaped
The limiting factors of this type of repair is:
- Concrete must be in fairly good condition – if there are too many cracks, replacement might be the only option
- New cracks can occur as the slab is raised up – most would have already been present, just not visible before lifting
- Possible resettlement – concrete poured on top of poorly compacted soils it can still sink further. This is also a possibility with a new concrete replacement slab.
The sequence for dealing with slab subsidence is:
- Establish what movement has occurred with the slab…use spirit level/surveyor levels
- Establish causation of the movement
- Rectify the cause if possible so problem doesn’t reoccur eg insert root barrier, fix stormwater pipes, stabilize soil bed etc
- Determine if this is a slab jacking or demolition project
For more information on Slab jacking see Bestunderpinning.com.au