ABSTRACT Paints provide protection against any possible corrosion by forming a thin film layer on the material surface. Paint is a colloidal system consisting of four main parts: binders, pigments or minerals, solvents or water, and additives. Minerals or so-called pigments with a proportion of 20 to 50 % by weight play a fundamental role on paint properties. The variation of these constituents gives rise to a fluctuation in paint type and its quality. In a general architectural paint, titanium dioxide (TiO 2 ) is used as a main white pigment with high refractive index but is quite expensive compared to the rest. Other minerals such as calcite and calcined kaolin are also used as filler or substitute for TiO 2 . Various researches on these minerals have been carried out in order to reduce TiO 2 consumption without affecting the paint quality. In present paper, the behavior of precipitated calcium carbonate (PCC) which differs from ground calcium carbonate (GCC) in terms of morphology and purity has been examined as a substitution for TiO 2 in paint mixture. The rheological properties of PCC along with the quality of paints produced by PCC was evaluated by standards based on both wet and dry paints such as viscosity, density, opacity and brightness. It was observed that PCC partly substituted for TiO 2 can improve the stability, scrub resistance, brightness and coverage of produced paints. 1 INTRODUCTION Paints are used to protect the material surfaces against various corrosions along with their decorative purpose. Consumption of waterborne paints increases since they are environmentally-friendly when compared to the solvent based paints. A typical waterborne paint consists of approximately 20% water, 30% binder, 10% agents and additives, and 40% pigments and minerals. In a dry film, however, there are just pigment particles and binder polymer fibers to keep the particles on the surface. As a consequent, the minerals used in the paint recipe directly affect the characteristics of the paint. TiO 2 is the main pigment used in the waterborne paints due to its high refractive index and coverage capability; nevertheless, its high price encourages researchers in paint industry to look for abundant and inexpensive substitutions. A number of minerals are used with the aim of decreasing the cost and improving some physical and mechanical properties of paints (McGonigle, 1996; Karakaş et al, 2009). Beside calcined kaolin, talc and other mineral fillers such as ground calcium carbonate (GCC) or calcite are widely used to lower the cost. Pigments proportion in paints could vary between 25- 35% (Wypych, 1999). GCC particles are Substitution of TiO 2 with PCC (Precipitated Calcium Carbonate) In Waterborne Paints B. Vaziri Hassas Istanbul Technical University, Faculty of Mines, Mineral Processing Engineering Department, 34469, Maslak, Istanbul, TURKEY F. Karakaş Istanbul Technical University, Faculty of Mines, Mineral Processing Engineering Department, 34469, Maslak, Istanbul, TURKEY M. S. Çelik Istanbul Technical University, Faculty of Mines, Mineral Processing Engineering Department, 34469, Maslak, Istanbul, TURKEY