Another four employees of waterproofing services company, TAC Contracts, have been jailed for giving kickbacks to building managers, supervisors, technicians and engineers of condominiums and commercial buildings here.

Sales and operations executive James Tan Gin Meng, 36, gave $42,818 in bribes, and sales manager Ng Kok Thai, 34, gave $59,074.50. Each was jailed for 46 weeks.

Another sales and operations executive, Alagappan Suriyanarayanan, 38, was jailed for 20 weeks, while sales executive Justin Heng Lye Chai, 35, was sentenced to 19 weeks' jail. Alagappan gave $36,839.50 in bribes, and Heng $31,076.

The four men pleaded guilty to corruption charges on Oct 23 and were jailed yesterday. The offences were committed between 2011 and 2014.

The mastermind, Donald Ling Chun Teck, 43, was the company's director when he gave $461,634 in bribes to 89 recipients between January 2011 and February 2014.

Most of the offences were committed with his 12 sales staff, including the four men sent to jail yesterday. With the latest sentencing, 11 of the sales staff have been dealt with in court.

Ling was sentenced to 2½ years' jail on Dec 22 last year on 20 counts of corruption involving $182,581, with 517 charges taken into consideration during sentencing.

During the hearing in October involving the four men, Deputy Public Prosecutor Asoka Markandu said Ling gave about 10 per cent of the contract value as corrupt referral fees to people such as management staff and contractors who were responsible for obtaining approval to award contracts to TAC. DPP Asoka added: "All the sales and operations staff at TAC... were aware of this corrupt business practice."

He told District Judge Jasvender Kaur that corrupt business practices can result in shoddy and sub-standard workmanship which may cause greater problems later.

Offenders convicted of corruption can be jailed for up to five years and fined up to $100,000 for each charge.