Author
VILLANUEVA, L
Prof. Dr. Arch. Universidad Politécnica de Madrid. Department of Construction and Architecture Technology. luis.devillanueva@upm.es
ABENZA, B
Arch. PhD. Student. Universidad Politécnica de Madrid. Department of Construction and Architecture Technology.
SANZ-ARAUZ, D
Lecturer Dr. MSc. MArch. Universidad Politécnica de Madrid. Department of Construction and Architecture Technology.david.sanz.arauz@upm.es

Abstract
Most of the façades in the historic centre of Cuenca, Spain, have been rendered with gypsum mortar. Local zoning regulations do not allow the restoration of house façades with any building materials other than the original ones. Therefore, builders have to use gypsum to render old houses exterior walls. However, the industrial gypsum plaster available in the market nowadays has quite different properties from the material made in traditional kilns in the past. New plaster is less resistant to humidity than old gypsum mortar. Tests have been carried out on the exterior walls to study their composition and materials. In order to perform the tests, three groups of houses built or repaired at different times (19th century, the 1980s and 1995) have been chosen. First, drawings showing the cracking were produced. Then, colour in the façades was catalogued and the layer composition studied. In addition, surface hardness and capillary absorption were also tested. In this work, a description of new non-destructive methods which have been used for this study can be found. These methods have enhanced learning about the rendering applied without damaging the walls. A detailed presentation of the experimental results is also included.

Key words
Cuenca, façades, gypsum, mortar, rendering.