Natural polymers have been used in ancient times to improve the durabi
lity of lime-based mortars and concretes. The natural polymers used we
re locally available. In this work, cactus extract from Mexico has bee
n tested in a Portland cement mortar. It is seen that cactus extract i
ncreases the plasticity of the mortar and improves water absorption an
d freeze-salt resistance. Calcium hydroxide produced by Portland cemen
t hydration interacts with the components of cactus extract, polysacch
arides or proteins, and forms complexes. It affects the crystallizatio
n process. Painting of the concrete with this extract has also shown i
mproved water resistance. (C) 1998 Elsevier Science Ltd.