Q. I am trying to clean and scuff (sand) primed aluminum to prepare for painting. An equipment supplier suggested trying shaved dry ice with a low percentage of particulate like nut shells or baking soda. The dry ice supplier we use does not provide that material. Have you heard of this treatment and do you know of a supplier of this material? Thanks, AF.
A. I am familiar with all these cleaning and pretreatment options individually, but not as a combination. Although not specifically mentioned, one of the first steps that should be considered is a degreasing process to remove any mill and forming lubricants that may be present.
Etching, sanding or otherwise abrading the aluminum surface is generally recommended to provide the best profile to the aluminum surface and optimize paint adhesion. The dry ice can remove small amounts of residual lubricant, primarily just very light mill oil that may be present from the cold rolling operation. Applied lubricant from forming or other metalworking applications will not be completely removed with the dry ice. The addition of the nut shells or baking soda can assist in the development of a surface profile. These would function similar to sandblasting, but leaving less residue behind. They will be equally as effective as the sanding, but could represent a time saving alternative.