Tuffs, classified as weak rock to hard soil with respect to their strength, slake on exposure, hence engineering problems occur as they weather and loosen. Weathering grades were determined in the field and in the laboratory using petrographic, chemical, physico-mechanical, P-wave velocity, and slake durability measures. Strong correlations were found between chemical weathering index, average porosity and fractal parameters based on the slake durability test results. The shapes of the tuff particles before and after the slaking test were investigated using the fractal dimension method to explain numerically the variations of the surface characteristics of the test samples due to weathering. Two fractal parameters are proposed for the second and fifth cycles of the slake durability test. The study has shown that for assessing the weathering state of tuffs, the fractal dimension approach could be a more effective tool than other methods of weathering grade determination.