Pre-cast concrete was used to replace serpentine stone in situ on an 1878 row-house in Washington DC. Because of its fragility, serpentine enjoyed only brief popularity; the article begins by discussing the stone's failure in this case. The decision to replace the stone with pre-cast concrete is based on its ability to match visual characteristics including colour. Each stage of the work is described: recording each stone; reproducing each one using latex moulding rubbes to copy surface characteristics, and casting each one using a wooden framework. A five-step concrete manufacturing process is presented with details of materials, quantities, sequences, and ASTM standards met. This is followed by a description of quality control, pouring, curing, salt-removal methods, and test and inspection procedures. Installation of stone and mortar is discussed. Project data - cost estimates, contractors, dates, etc. - are also provided.