Last year, soil walling to the partially built extension to the Bird in the Bush Centre on the Old Kent Road had to be demolished because the technique, recommended by the architect, was found to be 'problematic' and 'unacceptable', according to a High Court writ.
Work on the nursery extension began in August 2003 but was stopped shortly afterwards when, it is alleged, it became clear that builders would not be able to construct load-bearing walls of 'sufficient stability' using compressed earth.
The High Court will hear that an inspection revealed the walls were cracked and bowed, with numerous defects. The walls were found to be structurally unstable and needed substantially more maintenance and repair than conventional brick and mortar walls would have done.
It is claimed that subsequent research showed the walls had been built using unsuitable soil contaminated with wood, masonry, concrete and leaves, and were not square because they had been allowed to dry without adequate propping, the writ continues.
JM Architects is alleged to have breached its duties by suggesting that the rammed-earth technique could shave some 30 per cent off the standard construction costs. In fact, this method carries a significant risk of higher costs, the writ says, and JM Architects should have flagged up the risks of this 'novel' construction at an early stage.
The practice is also accused of misleading Southwark Primary Care Trust into believing that the rammed earth was sourced on-site, helping to save costs. Instead the soil was dug off-site at Gallagher's Quarry, Kent, where the earth was contaminated, it is claimed.
Other charges include failing to adequately prepare detailed proposals, and not compiling a feasibility study with due care and skill.
The writ concludes that the walls were entirely unsuitable for use in the project as a result of both their construction and design.
The primary-care trust was forced to flatten the nursery extension in 2006 and replace the walls with blockwork. The authority says its losses include the original cost of the project, remedial work, money paid to the nursery's operators - the Catholic Children's Society and Tower Homes - and legal and professional fees.
JM Architects was unavailable for comment.