  We study the stationary Stokes and Navier-Stokes equations with
non-homogeneous Navier boundary condition in a bounded domain
$\Omega\subset\mathbb{R}^{3}$ of class $\mathcal{C}^{1,1}$. We prove existence,
uniqueness of weak and strong solutions in $\mathbf{W}^{1,p}(\Omega)$ and
$\mathbf{W}^{2,p}(\Omega)$ for all $1<p<\infty$ considering minimal regularity
on the friction coefficient $\alpha$. Moreover, we deduce uniform estimates on
the solution with respect to $\alpha$ which enables us to analyze the behavior
of the solution when $\alpha \rightarrow \infty$.
