Conservation and Restoration on Cement-Based Renders of Built Heritage in Shanghai, PR China

Lime-based mortars were mainly used in buildings until the second half of the 19th century, when they started being increasingly replaced by a new binder: Portland cement. And then at the first of 20th century, the cement had become the key role as the binder of renders at Shanghai Modern historic architecture. Those finishing coats show different style: plaster (stucco), fair faced brick, stone coat, etc. The prevalent finish coats were applied with cement-based render as a result of economic way to imitate the stone texture, which includes the water brush stone (It is called Shanghai plaster as well later), pebble dash, artificial stone with chopping (called Zhanjiashi in Chinese), wet dash, Terrozzo, Mane brush drag Sgraffito (called Lamao in Chinese including different statement) at the first half of last century. Some former restoration on renders was discovered to replace the original materials and change the original texture or even the color since the research and analysis on the binder and aggregate was neglected, which is too far from authenticity principle. This paper aims to discuss the restoration method on cement-based renders by analyzing data of lab experiment with petrography and wet-chemical method. Instead of just simply repeating the principle quoted from established standards, the paper tends to provide realistic goals and information to get a more rational and sustainable restoration method in order to avoid the damage coming from unqualified restoration as well as get the authentic texture and color as original facade showed.