Volume modeling techniques are capable of modeling objects with possible change in topology and is widely used in virtual sculpting. A common practice is to provide shape-editing tools for adding or removing material from a volume model. However, sculpting may also involve the constant volume deformation of a model (e.g. the deformation of a clay model). This usually requires the use of physically based deformation of objects. An approach for deforming volume models is to use a spring mass approximation of the object, or the finite element modelling (FEM) technique. The spring-mass approximation gives a coarse estimation of the responses of the object, whereas the FEM approach requires generating solid meshes from the volume data. Generating a solid mesh from a volume model is a time consuming process. A modification in the volume data will require a solid mesh to be regenerated for the deformation process. In this paper, the boundary element (BEM) approach is adopted. Since the deformation is computed based on the iso-surface of the volume data, this eliminates the need for generating solid mesh from the volume data. By converting the deformed mesh to volume data, a deformed volume model can be further manipulated with existing volume modelling techniques.