Ask the Expert Question-and-Answer Archive

by Ron Joseph

August, 2009

Etching Primers for Aluminum Fishing Boat

Q. Ron, I have removed carpeting from my aluminum bass boat and intend to replace it with some rubber granule infused pait from Cabelas. Preparation calls for a primer over the aluminum prior to paint application and I've been told an etching primer is best to "chemically" bond to the aluminum. Is there a product I should consider using or simply go with the Cabela's recommendation of MP-10 water based metal primer, WB_MP by Tuff-Coat Manufacturing in California? Hate to be too technical but as they say, "it's all in the prep!"

A. You should use a two-part wash primer that you might be able to purchase at Ace Hardware. If not, you can purchase it in a professional paint supply store, such as Sherwin-Williams, PPG, etc. The wash primer contains some phosphoric acid and is water thin. You can only spray the wash primer and must ensure that the film thickness is 0.3-0.5 mils. Do not apply too much, because the primer will tend to spilt when you apply the full bodied primer over it. Do not use a brush or roller as you can't control the film thickness. I suggest you read the instructions on the paint label and follow them to a "T."

Good luck!

Q2. Thanks for the knowledge. I assume using a Wagner power sprayer would work? How does a novice know the thickness or ensure that I don’t exceed 0.5 mils? Is there a common reference that I could use to gauge the relative thickness during application as I’m unsure what .3-.5 mils "looks like?"

A2. You need to purchase an HVLP spray gun, definitely not a power washer. Perhaps, for a few dollars you can find a professional automotive painter in your neighborhood who can apply the wash primer for you. He will know how to apply a thin coating, and he should know what "thin" looks like. If you are a novice, you will not be able to apply a uniform thin coating ... that takes lots of practice. Since you don't have a dry film thickness gauge, your guide should be that the wash primer will be almost transparent. If you are willing to invest in a dry film thickness gauge I suggest you go to www.gardco.com and select a gauge that fits your budget. Please remember that the gauge MUST be able to measure thickness on non-ferrous surfaces. Do not purchase a magnetic gauge, because it won't work on aluminum.

Again, good luck.

Ron Joseph