U-POL High Build Primer, 450ml Aerosol, Gray. HIGH #5 is a ready to use high build primer/filler in an aerosol. It is used for priming uneven surfaces before top coating. High #5 is capable of producing a coating of a film thickness similar to that of a spray gun applied primer. The convenience of using a high build primer in an aerosol means that masking is kept to a minimum. Mixing paint and cleaning spray equipment are avoided as a result of using HIGH #5 leading to savings in time and materials. HIGH #5 is cromate free and easy to sand. This is really an outstanding product, KAS.. UP0791V