Macau's cultural heritage specialists have never gone to such great lengths to restore one building. It took them more than a year simply to make authentic plaster to repair the crumbling walls. But then Mandarin House is no ordinary structure in Macanese history. It was built in the 1860s as the residence of Zheng Guanying, a Qing dynasty (1644-1911) official known for his enthusiasm in pushing, and writing about, enlightened reforms. He is known to history as the 'son of Macau'. The house, spanning 3,700 square metres, is the largest of 29 architectural sites included in Macau's bid for Unesco World Heritage next month. 'These old buildings need to breathe naturally,' said Stephen Chan Chak-seng, the chief of Macau's Cultural Heritage Department. That is why he and his team of heritage specialists went to so much trouble to make plaster the old way. They did that by digging a hole in rural Taishan , Guangdong, and filling it with limestone and dried grass. One year later, the material had turned to powder - the basis for the old-fashioned plaster. 'Anything else, such as bricks or concrete, wouldn't have worked,' Mr Chan said. The quest for authentic materials led to the mainland, where oyster shells, tiles and various types of wood were collected for the $36 million restoration. In its glory days, the house was in an eminent neighbourhood. Zheng, the original owner, was quite a personage: he helped Sun Yat-sen deliver a petition to the Qing court's prominent administrator and general, Zeng Guofan, in the 1890s. While living in Macau, Zheng wrote Warnings in Prosperous Times, a treatise later admired by Mao Zedong . But with the passage of time, the Zheng family abandoned Mandarin House and it deteriorated, along with the neighbourhood. Now graffiti adorns a wall enclosing the nearby Lilau Square, one of the earliest Portuguese-style community squares in Macau. Ugly, decrepit five-storey residences envelop the historic jewel. The efforts of Mr Chan and his staff could be futile if long-term planning and immediate education do not defend the historical value, and address the tourism potential, of the entire neighbourhood. The solution may involve one developer, Trust Construction and Property Investment, which owns several developed and undeveloped lots surrounding Mandarin House. If the Unesco World Heritage bid is approved next month, the developer would be barred from building any new structures that might harm the historical value of the area.