Maintaining a heritage building is a lot harder than just slapping plaster and paint on the walls.

Take the 1860s St Andrew's Cathedral in City Hall for instance.

To concoct and develop the appropriate lime-based plaster to repair the place of worship, a trial formula had to be first applied to a small area in the cathedral.

This plaster formula was applied more than a year ago, alongside two other existing lime-based products in the market, as part of an ongoing trial. Time is needed to monitor how the different plasters perform with the historic fabric.

The process demonstrates how aged monuments require a lot of trial and error as well as significant technical know-how.

The cathedral enlisted Singapore University of Technology and Design's Dr Yeo Kang Shua, an architectural conservation specialist, to carry out the trials.

Last month, the National Heritage Board (NHB) rolled out two updated technical guides in response to calls to better aid monument owners and occupiers.

One provides a general overview on the responsibilities of being an owner or occupier. The other details technical information on painting a monument in easy-to-digest pointers and write-ups.

An updated guide on stained glass, and another two new guides on signs, as well as the care and treatment of Shanghai plaster, will also be issued this year.

In the paint guide, NHB notes that national monuments here are typically coated in three main types of paint - limewash, a mineral silicate paint that was first developed in Germany, and modern synthetic resin paint.

The guide says mineral paint is preferred because it allows buildings to "breathe" by facilitating the evaporation of moisture in the walls. Its application requires previous paint layers to be first removed and stripped to the plaster surface.

Singapore is home to 72 national monuments. The Preservation of Sites and Monuments (PSM), a division under NHB, is the national authority that advises on the preservation of nationally significant monuments and sites.

Mr Alvin Tan, NHB's assistant chief executive of policy and community, said one of the objectives of the nation's first heritage blueprint is to "support and empower" the owners and occupiers of these architectural and historical marvels. The blueprint will be published in April.

Monument occupiers said they hope more conservation expertise can be developed among locals to aid in the care of the Republic's ageing structures. They added that it might also be useful to have a forum where monument owners and occupants can exchange notes.

Ms Teo Lay Sie, group chief operating officer of UBS Singapore, welcomes the refreshed and new guides. UBS University has occupied the Former Command House monument at 17, Kheam Hock Road, since 2007. Ms Teo said they previously relied on old copies of approved works for pointers before planning maintenance works.

Among the Command House's antique fixtures are its chandelier and a Georgian lamp in the foyer.

She said: "These are antiques and the designs are no longer in production, so replacing a damaged or heavily corroded item requires sourcing the right vendor to fabricate an exact replica."