The conceptual block layouts generated by layout software packages very often yield detailed layouts with non-smooth material flow paths that have an excessive number of turns. Such non-smooth flow paths are not acceptable or feasible for actual construction. The automatically generated block layouts almost always have to be adjusted by layout design engineer in a labor intensive process. This paper presents a mixed integer programming model to modify a given block layout into a layout that allows the construction of smooth flow paths, while preserving the relative positions of the departments in the original block layout. Results of the computational experiments show that much smoother flow paths can be generated in the modified block layouts than those in the original block layouts. The suggested model can be solved within short computational time even for large industrial-sized block layout problems and can be executed without human intervention.