Is your house subsiding? Learnings from the Canterbury earthquakes
Concerns about earthquake-damaged homes have plagued Cantabrians since the devastating earthquakes of 2011. With earthquakes and extreme weather events increasing across the whole of New Zealand over the past decade, homeowners may be nervous about the possibility of their homes subsiding.
"Some of the most common symptoms of building settlement caused by subsidence or ground movement is cracking in the walls, whether that be in the gib internally or externally, in the brickwork or cladding," says Mike Baker, an area manager at Mainmark.
Mainmark is an internationally recognised specialist in earthquake remediation, liquefaction mitigation and ground-strengthening technologies. The company has successfully treated more than 30,000 sites in Australasia, from small domestic applications to large commercial, industrial, civil and mining projects.
"Any settlement of the building is ultimately bending or twisting the structure out of its original alignment and causing cracking in the visible surfaces," says Baker. "Windows and doors might be sticky, jamming or just simply don't operate as they should."
Baker says he often sees homeowners who have been paid out or settled with their insurer or EQC, not knowing what steps to take next.
"They know their house needs repairs but don't necessarily know who to contact first," he says. "If a customer contacts Mainmark we can quickly assess what work needs to be done to help get the house back to level."
Two of Mainmark's acclaimed technologies, which they use for residential and commercial re-levelling, are Teretek resin injection solution and JOG Computer-Controlled Grouting. Baker says both of these processes involve application methods likened to keyhole surgery to level-correct buildings and improve the ground immediately underneath.
"The processes do not require us to excavate any large holes, like some of the more traditional approaches involving jacks," he says. "The biggest drill hole we need to complete the job is 40mm in diameter, just a little bigger than a $2 coin, often as little as 6mm in some circumstances from inside a home. Once the level-correction is complete, the area is ready for use almost immediately. Many projects only take us a matter of a day or so to complete, depending on scale."
The processes involve using handheld drills to create small holes in the footings and floor slab, through which the resins and grouts are injected. This gently increases the volume of the soils. Millimetre by millimetre, the building is brought back up to level.
Homeowners can often remain in the property, as there is little to no mess, no damage to the garden and no disruption to neighbouring properties.
Since many Cantabrians have been told their houses would need to be demolished and rebuilt, Baker says he is proud that Mainmark can offer them a way to save their homes.
"By using Mainmark's solutions, homeowners are able to achieve a great outcome which enables them to keep their home and return it back to pre-earthquake condition.
"Not to mention, for a fraction of the price of a complete rebuild."