The study of fly ash as a replacement to mortar workability using a fl
ow table is presented. Flow table spread (FTS) values were measured an
d correlations among fly ash replacing percentages, water volumes and
granulometric distributions of fly ashes have been established. Linear
relationships between FTS values and water volumes were obtained in t
he 200-225 mL water range (0.5 water/cement + fly ash ratio, 3.0 natur
al sand/cement + fly ash ratio). An increase of water volume implies g
reater FTS values. Original fly ash was separated in four fractions wi
th different granulometric distributions. FTS values increase as do sp
ecific surface, and FTS values decrease as mean diameter of fly ash in
crease. For the finest fraction, the lubricant effect was counteracted
by water adsorption on fly ash particles surfaces. The shape distribu
tion curves of fly ashes (original and their fractions) has an importa
nt influence on workability.