Here we study the nonnegative solutions of the viscous Hamilton-Jacobi problem [ \left{ \begin{array} [c]{c}% u_{t}-\nu\Delta u+|\nabla u|^{q}=0,\ u(0)=u_{0}, \end{array} \right. ] in $Q_{\Omega,T}=\Omega\times\left( 0,T\right) ,$ where $q>1,\nu\geqq 0,T\in\left( 0,\infty\right] ,$ and $\Omega=\mathbb{R}^{N}$ or $\Omega$ is a smooth bounded domain, and $u_{0}\in L^{r}(\Omega),r\geqq1,$ or $u_{0}% \in\mathcal{M}{b}(\Omega).$ We show $L^{\infty}$ decay estimates, valid for \textit{any weak solution}, \textit{without any conditions a}s $\left\vert x\right\vert \rightarrow\infty,$ and \textit{without uniqueness assumptions}. As a consequence we obtain new uniqueness results, when $u{0}\in \mathcal{M}{b}(\Omega)$ and $q<(N+2)/(N+1),$ or $u{0}\in L^{r}(\Omega)$ and $q1,\lambda\geqq0,$ and $u$ is a signed solution.
