How do you go about building up bondo, mud, plastic fillers to custom build a fender flare. How much is to much mud and how do you get it to hang on without shrinking/cracking? I'm working on a 65 Chevelle thats been quartered and skinned. Someone started to build fender flares with plastic filler. The mud that there is about 1/4 in thick. A grinder was used in several places on the body to tell the depth of the mud and I want to fill it back in and have it stay. <img src="confused.gif" border="0">