Renovation contractors say a new rule requiring pre-packed cement to be used throughout Housing Board flats could add thousands of dollars to customers' bills.
Since last month, it has been compulsory for them to use pre-packed screed on the floors and walls of bedrooms and living rooms.
All flat owners who signed their renovation contracts on or after June 1 are affected.
Pre-packed material was previously mandatory only in wet areas such as toilets and kitchens, but an HDB spokesman said that the rule was extended to "ensure a cleaner environment and more uniform finishes".
Contractors say the new rule will drive up renovation costs by about $2 to $3 per square foot, with some estimating that the increased total could be as much as $3,000.
Before the regulation kicked in, contractors would manually mix cement, sand and water on-site to do up floors and walls.
With pre-packed screed, which is blended to the required proportions at the factory and requires minimal on-site preparation, contractors will now just have to add water to the mix to use it.
The HDB spokesman added that other benefits of pre-packed screed are a higher quality of finished work and less material waste.
The regulation was initially due to take effect last December and renovation contractors were first told of the change a year ago.
But many asked the HDB for more time to prepare. Said Mr Tan Chim Hoon, president of the Singapore Renovation Contractors and Material Suppliers Association: "We had to buy the pre-packed screed in bulk and work out how we should charge our customers."
Mr Tan, who has 40 years of experience and runs renovation firm Hoon Hoe Bros Renovation and Trading, added: "Pre-packed screed is definitely more costly than raw sand and cement."
The HDB spokesman said the use of the pre-packed material "makes up a small part of the overall renovation costs".
It added that it checked with the industry and estimates that renovation works for a five-room flat will cost about $1,500 more, although this also depends on the extent of renovation works and labour costs.
Mr Yeo Eng Hock, 52, who runs Reliance Furniture and Renovation, said the traditional method of mixing cement and sand depends on a worker's skills.
"Consistency can be a problem," he said. "With the pre-packed screed, everything is mixed in a standard ratio."
Mr Yeo said his workers find the pre-packed material stickier, harder to use and more time-consuming. "But it's probably because we are still getting used to working with the material in large areas. It should get better."
Associate Professor Tan Teng Hooi, head of SIM University's building and project management programme, said the use of pre-packed screed should lead to higher quality for flat owners.
He added: "The old method of manually mixing sand, cement and water depends largely on personal judgment or trial and error. Using pre-packed material will ensure better quality in terms of consistency and finishing."
Mr Jon Nio, 29, will move into his four-room flat in Clementi once renovation works are done. The public relations consultant signed his renovation contract in early May and so is unaffected by the new rule.
"I'm glad I'm not affected because every cent counts," said Mr Nio, who expects to pay about $35,000 in renovation costs. "The extra money spent on the pre-packed screed could cover items such as a washing machine and television set."