By 1825, Spark's trading business had greatly expanded, and he was chartering ships to coastal trade routes. A year later, his business had grown even more, and he started a shipping agency. Through this agency, Spark sold incoming cargoes, exporting stores to places such as Hobart, colonial produce to Calcutta, and wool consignments (the first of what would be very many wool consignments) to London, backloading merchandise when it was possible. Additionally, Spark worked as a sort of agent for farmers and country settlers by purchasing their produce and selling them supplies such as livestock and stores, as well as the occasional ploughman or overseer. At this particular time, Spark owned more than six thousand acres (24 km2) of land on the Hunter River and a nine-acre (4 hectare) grant at Woolloomooloo; Spark had developed a passion for land ownership. In 1835, the designer John Verge (who also built Elizabeth Bay House) helped Spark complete his property, now named Tusculum outside of Wolloomooloo Hill (now known as Potts Point). It now houses the Royal Australian Institute of Architects.