The Weibull statistics are extensively used in the last years to estimate the reliability of fracture data of brittle construction materials such as ceramics, which tend to present a large scatter in mechanical strength. In the present research, clay-based building ceramics incorporating industrial solid by-products were fabricated employing a pilot-plant simulation of industrial brick manufacturing and their flexural strength was evaluated by three-point bend testing, before and after subjecting the bricks to 25-cycle frost resistance testing. Then, the modulus of rupture was calculated and analyzed using Weibull distribution. Industrial powders including different fly ash samples and steel making dust were utilized as substitute secondary resources, mixed with standard brick clays and water, and extruded into rectangular brick specimens, which were sintered in a controlled furnace. Weibull plots of the results allow the prediction of the stress, at which the probability of survival of the ceramic bodies is kept to a certain value. The relative clay/by-product mixture composition, sintering temperature and residual porosity are proved to affect the brick bending strength and reliability. Porosity depends on the specific pore-forming agent used as well as on the sintering temperature. In conclusion, Weibull analysis appears to be of particular importance to assess the quality of ceramics incorporating industrial solid by-products.