Background: An outbreak of silicosis occurred—despite periodic health surveillance—in a plant producing novel applications of silica-based composites. Methods: Five workers were referred to our clinic for occupational medicine. Using past spirometry data from periodic health surveillance, we calculated individual yearly declines in FEV1 and FVC using robust multivariable linear regressions. Respirable quartz was measured in the workplace (after the first case had been diagnosed). Results: The five men (38 to 59 years), all ex-smokers, had been employed for 8 to 30 years at a Belgian company producing skirting boards—made from a polyester-silica composite material—for use as hygienic wall protection in food/pharmaceutical industry. We diagnosed enlarged mediastinal/hilar lymph nodes without radiological lung involvement in one worker, simple silicosis in two workers (one also with emphysema), and progressive massive fibrosis in two workers. Periodic spirometries—but no chest X-rays—had been performed since 8 to 10 years prior to diagnosis. The four men with silicosis proved to have undergone excessive declines in FEV1 (98 to 221 mL/year) and FVC (17 to 220 mL/y). High respirable quartz concentrations (>100 µg/m³) were measured during various operations, especially during dry finishing of the cured skirting boards (1,080 µg/m³). No personal respiratory protection was used. Conclusions: The outbreak shows that the hazards of silica-based artificial stone production/processing reach beyond the kitchen/bathroom countertop industry. Improving prevention and establishing workers’ health surveillance programs—or improving the quality of existing programs—are crucial.