The paper starts with a survey of the historical background of this small Spanish church whose apse was dismantled in 1957, transported to New York City, reassembled there with old and new stones cut in Spain. In 1966 it was observed that in spite of a 1958 treatment (immersion in solutions of MgFub>6Si and Ba(OH)ub>2) the stones -- a yellow dolomite limestone -- were flaking and soluble salts were efflorescing on their surface. A new treatment in 1969 followed study and testing and a provisional shelter was built around the apse in 1971. Deterioration has continued due to crystallization of soluble salts occuring in areas where water seeps through the shelter. The geological and petrographic characteristics of these stones are studied, their chemical and mineralogical composition is analyzed as well as their density and porosity. A detailed chemical analysis of the efflorescences and soluble salts is given, the biological growths are analyzed. Four water repellent resins were tested. A table illustrates the resin uptake of the stones, showing great variability of absorption by a single block. The main causes of deterioration are deduced from this study and a series of eight recommendations presented for the conservation of the apse. The results of practical work begun in the spring of 1986 will be reported at the time of the Congress. A list of materials is appended.