Here's a cool timesaving tool. Holloway used a file often called a cheese grater to cut the high spots of the filler just before it is fully hardened. Once fully dry, the filler is extremely hard and can require a serious workout just sanding through the spreader lines. use a cheese grater to cut down the high spots in the filler while it still feels tacky, but no longer squishy. It will save a lot of time and effort.