Earthquake damage could be hiding under the floors of pre-1970s homes in Christchurch, an earthquake lawyer says.

Peter Woods, a partner at Anthony Harper, held a meeting for affected homeowners on Monday night, with the invitation specifying that no insurance company affiliates could attend.

Strategies used to repair such homes following the Canterbury earthquakes were failing and causing additional damage, he said.

GEORGE HEARD/FAIRFAX NZ Earthquake lawyer Peter Woods held a meeting seeking interest in legal action against insurers regarding rubble foundations.

Woods was carrying out an independent survey to establish the range of issues being dealt with in pre-1970s homes.

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Many of the homes had problematic rubble foundations, he said. Most of the rest of the country stopped using the foundations made of stones and other rubble encased in varying grades of concrete, aggregate and plaster in the 1920s.

GEORGE HEARD/FAIRFAX NZ Disgruntled earthquake insurance claimants gathered on Monday to learn about pre-1970 rubble foundations that may have been damaged in the Canterbury earthquakes.

Woods said about 65 per cent of Canterbury homes had rubble foundations.

"We are hearing about owners experiencing floors that are sagging, dropping and bowing. More often than not, the only sign of earthquake damage is the damage you can see on the plaster finish on the outside of the perimeter foundation."

Licensed foundation specialist Bevan Craig was helping earthquake claim advocacy group EQC Fix with its work on rubble foundation repairs.

Craig said damaged rubble foundations could potentially be a "multi-billion dollar problem" for the region's homeowners.

He said the meeting was not specifically to begin a class action, but people with similar problems should "club together" to find solutions.

Guidelines given to insurers in 2013 by the Ministry of Building, Innovation and Employment (MBIE) were not appropriate for these foundations, he said.

MBIE's advice was that "if a house looks reasonably level and the cracks to its ring base are no larger than the 5 millimetre tip of a pencil, then it is probably safe to put it down as a cosmetic fix", Craig said.

Cosmetic fixes often involved waterproof filler and pain, or epoxy resin for larger cracks.

Craig said that was like trying to glue together a plate that had been trodden on and crushed.

"You wouldn't bother trying, would you? And that's what happens to the rubble foundations after an earthquake."

Woods said he had seen a large number of cases where foundation repairs had failed or were never done, despite being signed off as completed.

"People are noticing cracks appearing in inside walls, or slumping happening on one side of the house.

"We have one family in a 1915 house with a rubble foundation, with all those things happening plus their internal walls are now bowed."

He said EQC reduced the repair estimate for the property from $800,000 to $52,000, and most of the cost cuts were in foundation repair.