Artificial and natural weathering in conjunction with scanning electron microscopy (SEM) was used to study the effect of surface finish on the resistance to deterioration of GRP sheets. When exposed in a xenon arc weathering machine or to outdoor weathering, GRP sheets protected with either a gel-coat or an acrylic lacquer have considerably better resistance to deterioration than sheets with smooth, unprotected surfaces (conventional finish). Temperature-humidity cycling in conjunction with thermal gradients cause no deterioration in gel-coated sheets, but induce cratering in those coated with an acrylic lacquer. Sheets with conventional surface finish undergo usual deterioration in artificial or natural weathering after relatively short periods of exposure. -- CAL