Why is it important to select the correct grit when sanding plastic fillers?

Selecting the correct grit when sanding plastic fillers is vital for achieving the desired smoothness of the surface. The grit of sandpaper determines the roughness or fineness of the sanding action. Using a coarse grit initially helps to quickly remove excess filler or smooth out uneven areas, while subsequently using finer grits helps refine the surface, eliminating scratches and imperfections left by the coarser paper.

Achieving the proper level of smoothness is essential before applying paint or other finishes since any irregularities can be visible once the final coating is applied. A smooth surface not only improves the appearance of the repair but also enhances adhesion for any subsequent paint layers, ultimately leading to a more professional-looking result.

While other factors like paint damage, the ease of sanding, and the bonding of fillers are important considerations, the direct impact of grit selection on the smoothness of the surface being prepared is a primary reason for its importance in the sanding process.