  The well-known idea to construct domain wall type solutions of field
equations by means of an expansion in the width of the domain wall is
reexamined. We observe that the problem involves singular perturbations.
Hilbert-Chapman-Enskog method is used to construct a consistent perturbative
expansion. We obtain the solutions to the second order in the width without
introducing an effective action for the domain wall. We find that zeros of the
scalar field in general do not lie on a Nambu-Goto trajectory. As examples we
consider cylindrical and spherical domain walls. We find that the spherical
domain wall, in contradistinction to the cylindrical one, shows an effective
rigidity.
