This article reconstitutes interaction situations which took place in 2004 in a small Barcelona building site between undocumented workers, their boss, and a young 26 years old French anthropologist. The present writing explores the different perceptions of gender, class and race as perceived by the actors of a small building firm, where the low-skilled workers had not signed a work contract. The intersectionality concept was used here within the frame of ethnographic data production. The account of the investigation reveals that the actors use gender, class and race properties making them intervene in sometimes unexpected compensation logics. The articulation of these properties refers to a configuration of power which cannot be summed up through a vertical logic of power, whether that of a boss who exploits and dominates without mercy undocumented workers or that of an anthropologist who imposes, without obstacle, his own investigation to vulnerable investigated people.