Common culprits include using worn-out sandpaper, applying uneven pressure while sanding, or sanding against the wood grain. Understanding these causes is crucial for effectively preventing pigtails and achieving a flawless finish. Fiberglass surfaces, with their sleek and glossy appearance, are a true testament to modern craftsmanship. Enter the realm of water sanding, a. Pigtails are pesky imperfections that manifest as spiral-shaped marks on sanded surfaces, resembling the corkscrew tails of, well, pigs. Woven roving is typically layered with chopped strand mat as it will help fill in the large gaps found in this heavier fabric.