Timber floors with insufficient strength and stiffness can be upgraded by applying a concrete topping to form a composite structure. Conventional upgrades have a topping thickness of 40 mm or greater but recent research has proposed an alternative thin topping solution (20 mm). The shear connectors which transfer the forces between the timber joists and concrete topping are critical to the success of the upgrade. This paper presents the results of pushout testing of thin topping timber-concrete composite joints. A factorial experimental design was employed to assess how the inclination, topping thickness and timber density affect the stiffness and strength of screw joints. The results were statistically assessed to differentiate between the effects of each factor and establish the presence of interactions between factors. The screw inclination and topping thickness were found to be important factors when considering the stiffness of the joints. Topping thickness was the most critical factor for the strength of the joints.