My ten year old fiberglass swimming pool had a dark line at the water line that was hard to keep clean.  I lowered the water level when I winterized the pool and used this to polish the clean and seal the top 18" of gel coat around the perimeter of the pool.  A dime size drop of wax will clean a 24" x 18" section.  Wipe it on with one rag, buff it off before it dries with another rag.  Repeat until you get around the pool.  You can feel the difference in the surface of the gel coat immediately.  Looking for ward to next years pool season.