Abstract Freezing of superheated water around an isothermal, horizontal cylinder has been studied experimentally. The shadowgraph technique was used to visualize the flow (plume) development in the water, and the contour of the ice layer around the heat sink was recorded photographically. Freezing of water was always accompanied by natural convection and produced nonuniform ice growth. Benard-Goertler instabilities resulted in secondary flows which produced waviness (nonuniform) ice growth along the axis of the cylinder. The number, location and magnitude of the ripples were found to depend on the initial water superheat and on the heat sink temperature.