The purpose of the flash coat is to prohibit too much of the solvent from being absorbed into the epdm rubber. This light coat that many times will dry within an hour will block any additional solvents from being absorbed into the rubber.
If you do not first apply a flash coat you run the risk of too much solvent being absorbed which will cause the coatings to swell. This will cause additional days in the time it will take to reduce in size.
