Microgels suspensions such as Carbopol ones are commonly used as a viscoplastic fluid model in fluid mechanics experiments. Polymethyl methacrylate (PMMA) walls are also frequently used in these experiments since it enables flow visualizations via their transparency properties. When sheared with smooth surfaces, the microgels slip on the surfaces and an apparent motion of the fluid occurs below the bulk yield stress $\tau_y$. This motion stops at a sliding yield stress $\tau_s$. The occurrence of this apparent slip below $\tau_y$ can modify significantly the flow features. This article presents a PMMA treatment to inhibit the slip of the Carbopol microgels. The method is simple to perform, independent on the treatment conditions and stable in time.