Abstract
	This paper deals with the influence of base ceramic raw materials on the thermal expansion coefficient (TEC) of tile bodies and verifies the validity of additive function of dilatation for the polycrystalline ceramic materials produced by the single fast fired technology. This information is necessary for technologists in order to control the composition of ceramic mass and to select the suitable glaze. 
	The TECs were measured on five clay bodies. The different dilatation curves provide the possibility to prepare several ceramic masses with various dilatation properties. The TEC values of four non-mouldable raw materials were calculated for fired-on-phase providing that dilatation properties are additive.
	Thermal expansion of five ceramic masses prepared from above nine raw materials were measured in the temperature interval 20 - 600 °C. The validity of additive functions of dilatation ? = ? ?iV i and ? = W1.?1 + W2.?2 + ... + Wn.?n was verified for the ceramic porous wall tile bodies. In the case that quartz from the sand (non-plastic raw material) is in the crystalline phase after firing and it does not contribute considerable to the formation of amorphous glassy phase the results of calculations are comparable with the measured values. Both equations give practically the same and correct values.
	The accuracy of calculations depends on the exact estimation of degree of conversion of quartz into the glassy phase. Their amounts are influenced by the firing process and composition of input raw materials. Also more technological parameters need to be taken into account in designing of composition of ceramic masses. For that reason none of the tested masses could conform both technological parameters and required tile bodies properties, namely TEC(20-600°C) of body.