The use of industrial waste materials as additives in the manufacture of ceramic products has been attracting a growing interest from researchers in recent years and is becoming common practice. This work describes the changes in the behaviour of the clay material used in a ceramic industry due to addition of grog, produced in ceramic industry. Mixtures of clay and waste material (0–50 wt. %) were uniaxially pressed and sintered at temperature 1000°C. Results from chemical, mineralogical and morphological analyses (XRF, XRD and SEM), water absorption and compressive strength show that the grog can be added to the clay material with no detrimental effect on the properties of the sintered fire-clay products. The test results indicate that the grog could be used as filler in ceramic bricks, thus enhancing the possibility of its reuse in a safe and sustainable way.