We study an initial boundary value problem for a heat equation with strong absorption. We first prove that the solution of this problem stays positive for any finite time and converges to the unique steady state for a large class of initial data. This gives an example in which the dead-core is developed in infinite time. Then some estimates of the dead-core rate(s) are derived. Finally, we provide the uniformly exponential rate of convergence of the solution to the unique steady state.