The objective of this study was to quantify the proportion of kneeling work activities among floor layers and to assess external knee joint forces in five different kneeling work positions. Thirty-three floor layers were videotaped discontinuously and four floor layers were videotaped continuously for a whole working day. External knee forces were measured in five different kneeling work positions in ten floor layers using Computer Dynography. The study showed that floor layers spent a high percentage of time in knee-straining work positions. Kneeling work tasks, particularly gluing and crawling caused high external knee forces ranging from 0.3 Newton (SD 0.2) times body weight when floor layers were kneeling back on the heels, to 3.5 Newton (SD 0.3) times body weight in the crawling work position. The study highlights the need for prevention by minimizing the amount of kneeling work positions among floor layers.