Owners in Sydney's Mascot Towers face delays and another million-dollar bill as urgent work is needed to restore the cracked building's foundations.
Ground engineers will begin urgent chemical grouting injection works on Monday to ensure soil under the building's foundation slab can bear the force of remediation works from above.
The owners in the problem-plagued, 132-unit complex will be asked to approve the $1 million bill at a meeting on Tuesday night, the building management said on Saturday in a letter marked "strictly confidential".
Owners had previously been warned voids and areas of "very loose sand" had been found under the slab.
Residents were ordered out of the decade-old building in June after cracks in the primary support structure and facade widened.
Recent advice from a structural engineer suggests those cracks have continued widening.
Primary propping works is under way to reduce the pressure on some beams will be under during the upcoming summer when the building's materials expand and contract.
Additional propping work - set to cost $4.95 million - will not begin until after the soil work is completed.
A $7.7 million special levy on owners was approved in August to fund propping works.
The building managers said the urgent under-slab work should avoid any further deterioration of the structure and ensure permanent remedial works are successful.
While those permanent solutions are currently undecided, one possibility is steel fibre reinforcement.
A cost is not known but building managers say it isn't expected to exceed what has been spent on the foundation and primary propping works.