This study was to find the effect of holding time on the compressive strength of fired slabs produced from ball clay obtained from Ntawoclay deposit in Mukono District, in central Uganda .The chemical composition by percentage weight of the clay was analyzed based on x-ray diffraction pattern obtained using RIX 3000 Spectrometer machine. The clay samples wereproduced from clay slurry of particle size of 45μm. The dried samples were fired in electric furnace to temperatures of 5000C, 6000C, 7000C, 8000C, 9000C and 10000C.The temperatures were held for holding times of 20minutes, 30mintes,40minutes 50minutes and 60minutes..and allowed to cool to room temperature in the furnace. The compressive force required to break the fired slabs was measured using 500SN-1299417 machine. The breaking forces were converted into the compressive strengthof the slabs to find out how holding time affected compressive strength of the slabs..A null hypotheses, H01- that compressive strength of fired clay does not depend on holding time when fired to various firing temperatures at ∝ = 0.01 and ∝ = 0.05 levels of significance. The Ntawo ball clay was found to contain 67.2% of silica, 18.2% of alumina, 2.83 % of Fe2O3 and 1.84% of sodium, calcium and magnesium fluxes. The compressive strength of the slabs was found to decrease from 4.2% to 0.4% with holding time for firing temperatures between 500℃ and 800℃. The compressive strength variation was negligible, less than 1% for temperatures beyond 900℃ to 1000℃. The compressive strength of ball clay beyond 800℃ does not need longer holding time because according to this study will not affect the compressive strength. The compressive strength for ball clay fired beyond 1000℃ and 60 minutes is worth investigation to find whether any change in the mineral compounds of ball clay can affect the above results.

Keywords : Holding Time; Firing Temperature; Fired Clay Product; Compressive Strength.