Ask the Expert Question-and-Answer Archive

by Ron Joseph

January, 2002

Surface Preparation For Etch Primer

Q. What is the best pretreatment before etch primer application (for galvanized steel)? Now we apply solvent, wiping with solvent.

A. The degree of surface preparation depends on the nature of the galvanized surface. Sometimes, galvanized steel is shipped with a temporary corrosion preventative oil or other "coating." If so, this layer must be removed before you apply the etch primer. You might need to check with the vendor of your galvanized product to see if anything has been applied. Solvent wiping might be adequate, or you might need a hot water-detergent to remove the coating. Frankly, if you can avoid using solvents, you will be cutting down on air pollution and the emission of VOCs into the air.

Alternatively, you might find that scuff sanding with an abrasive and a Scottbright pad or steel wool will do the trick. If you use steel wool you MUST make sure to thoroughly rinse the surfaces to remove any traces of the steel wool, otherwise the remnants will rust.

Once you are sure that you have a "virgin" galvanized surface, you can apply the etch primer. Are you aware that waterborne etch primers are now available? Whenever possible we prefer to recommend the waterbornes in favor of the solvent-based pretreatment etch primers, because the latter have VERY high solvent contents and are severe polluters of the air.

Regardless which method you use to clean the galvanizing, and which etch primer you select, we always strongly recommend that you perform some tests first to insure that you get the adhesion and long term performance that you require for your product. Please do not simply follow our advice without first performing some tests to confirm the recommendations.