Materials and Structures / Mat6riaux et Constructions, Vol. 37, August-September 2004, pp 472-479 Mould and phototroph growth on masonry fa :ades after repainting M. A. Shirakawa ~, V. M John 2, C. C. Gaylarde 3, P. Gaylarde 4 and W. Gambale 5 (1) Dept. of Pathology, Centro de Ciancias Biol6gicas, Universidade Federal do Parfi, Bel6m - Parfi, Brazil (Formerly at Escola Polit6cnica, Universidade de Sgo Paulo, Brazil) (2) Dept. of Civil Construction Eng., Escola Polit6cnica, Universidade de Sgo Paulo, Sgo Paulo, Brazil (3) Dept. of Biophysics, Faculdade de Bioci~ncias, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil (4) MIRCEN, Dept. of Soils, UFRGS, Porto Alegre, Brazil (5) Dept. of Microbiology, Instituto de Ci~ncias Biom6dicas, Universidade de Sgo Paulo, S~o Paulo, Brazil ABSTRACT The appearance and durability of paint films are affected by microbial growth and fungi and phototrophs are considered to be especially important, degrading the films mechanically, by the production of metabolites, chiefly acids, and by enzymatic activity. In this study, fungi and phototrophs were identified before and throughout one year after painting two building fagades in S~o Paulo. Disinfection with hypochlorite and high-pressure water jet cleaning of the fagades caused reduction of at least 85% in the microbial population. Paint was applied with or without a biocide formulation (0.25% w/w) - carbendazin, N-octyl- 2H-isothiazolin-3-one and N-(3,4-dichlorophenyl)N,N- dimethyl urea. The biocide reduced fungal colonization up to 10 months after painting on one building. However after 12 months biocide made no statistically significant difference. The major fungal contaminant was the genus Cladosporium. After 10 months Aureobasidium was also associated with black discoloration. On both the re-painted fagades, fimgi were detected before phototrophs, contrary to the citations from the literature. SEM showed that fungal contamination was present not only on the surface, but between the old and new paint films and between old paint and rendering mortar. Under these conditions building fagade details and micro-environment seem to be more important than biocide in controlling fungal growth. RI~SUMI~ L 'aspect et la durabilitd des films de peinture sont affectds par l'action microbienne, les mycktes et le cyanobacteria dtant considdr~s comme particulikrement importants, par la d&gradation mdcanique des films due 5 la production des mdtabolites, notamment les acides, et par l'activitd enzymatique. Dans cette dtude, des mycktes et les phototrophiques ont dtd identifids avant et tout au long de l'ann~e qui a suivi la peinture des fagades des deux ~difices de S~o Paulo. La d~sinfection de lafagade par l'hypochlorite et le nettoyage h haute pression par jet d'eau ont caus~ une rOduction de 85% de la population microbienne. Ensuite, la peinture a ~t~ appliquke avec ou sans formulation de biocide (carbendazin, urOe de N-octyl-2H- isothiazolin-3-one et de N-(3,4-dichlorophenyl)N,N-dimethyl 0,25% re~m). Le biocide a r~duit la colonisation fongique jusqu ~ 10 mois. Cependant, aprks 12 mois, le biocide n'a pas prOsentk de difference statistiquement significative. Le contaminant fongique principal ktait le genre CladosporiurrL AprOs 10 mois, l'Aureobasidium a ~tO Ogalement associO h la d~coloration noire. Sur les deux fagades peintes, des mycktes ont ktO d~tectOs prOalablement aux phototrophiques, contrairement aux citations de la litt~rature. L "observation au MEB a montr~ que la contamination fongique Ota# prOsente sur la surface, entre le vieux film et le nouveau film de peinture et entre la vieille peinture et le mortier du rev~tement. La conclusion de cette ~tude est que l'influence du micro-environnement et des earact~ristiques de la fagade semble ~tre plus importante que l "action du biocide ajustOsur la croissancefongique. 1. INTRODUCTION The development of discoloration on painted surfaces is a very common phenomenon. Although such discoloration is sometimes non-biological in origin, it is most commonly caused by various microorganisms [1, 2], including autotrophic bacteria (those that do not need organic compounds as carbon source), heterotrophic bacteria (which 1359-5997/04 9 RILEM 472