Characterization of the Mortars of El Castillo De San Cristóbal

This study characterizes the formulation of mortars used in the construction of Fort San Cristóbal Located in the city of Old San Juan, Puerto Rico. Renders, horizontal surface mortars, and bedding mortars representing a period of time from the late 17th to the early 20th century were sampled from a variety of outworks on the site. Results of examination using optical microscopy/polarized light microscopy and x-ray diffraction show that mortar formulations were closely tied to their uses as well as their time periods. Evidence is presented that the Spanish were using hydraulic brick dust mortars during the second phase of construction at the fort in the late 18th century, in reaction to earlier failure of weak clay/lime mortars