Aluminum Siding – Paint and Primer Tips
|UPDATE: New information regarding painting aluminum has been added to this column. Be sure to check the Author's Notes following the article.|
Painting Aluminum Siding - It's Easy
You can paint aluminum siding. It's important to realize you have to clean off all the chalking factory paint before you apply the new paint.
Ammonia + Aluminum = Trouble
Virtually all water-based paints have some ammonia in them. Don't ask me what it does, I just know it's there. Anyway, it just so happens that ammonia and oxidized aluminum don't mix very well. In fact, when you mix the two things together a chemical reaction occurs that produces gas. This is just fine in a chemistry lab but not on your siding.
Some books and magazines on painting recommend that you prime aluminum siding and/or paint over existing aluminum siding with water-based primers. This can spell disaster. The problem is that there are quite possibly pinholes or cracks that are not visible to the naked eye where the old aluminum paint has worn off. The aluminum could have been exposed to the air for quite some time. It is oxidized. If you paint this aluminum with a water-based primer, you may create a problem. Small bubbles may form under the paint skin. This could lead to premature film finish.
Oil to the Rescue
Did you know paint companies employ chemists? These individuals know that you must create a barrier between the oxidized aluminum and the water-based acrylic finish paint. It is easy to do.
Virtually every paint manufacturer makes a high-quality oil-based metal priming paint. This is the product to use to create the barrier. However, it is not necessary to apply the primer full strength. In fact, thinning it down actually helps the primer penetrate deeply into the eroded paint finish on your siding.
The trick is to thin one gallon of paint with one pint of thinner. Be sure to use the approved thinner! Don't use gasoline, or some other solvent you think will work. The label on the paint can usually tell you exactly what to use.
The key to any successful painting job lies in preparing the surface. The surface to be painted is the foundation. Poor foundations create poor results. This is true in any project. Clean surfaces are the key. If you remember that paint is simply a modified glue, you will be on the right track. Glue likes to stick to rough surfaces - there is more surface area. Glue doesn't like dust. If you follow some of my painting tips, your upcoming paint job will last and last!
You can buy some clear acrylic primers that will not bubble. They are made for old painted aluminum surfaces. William Zinsser makes one called Peel-Stop.
Author's Notes: The following updated information was received from the Paint Quality Institute. Debbie Zimmer addresses ammonia in latex paints and the resulting bubbling.
Thanks so much for your questions and comments. Regarding ammonia in latex paints, it is so low today that the off-gassing (resulting in bubbling) is really not a factor.
Here are a few detailed points to consider:
1. Bare Aluminum: forms a strong oxide layer which is easy to stick to and is relatively inert to ammonia. Some folks confuse ammonia with acid. Yes --- acid will generate some hydrogen gas but there should not be a reaction with ammonia.
2. All Aluminum Siding is coated. This again generally results in a surface that is easy to stick to but for all intents and purposes, relatively inert to water-based paints. Even under poor conditions, incidental exposure to Aluminum should not be a problem because of above (1).
Also, on occasion, we do speak about oxygen bleach but typically use the more common (common to homeowners) "bleach" term. Perhaps we should use oxygen bleach more often. We don't use brand names (in any of our materials), such as Clorox.
Tim, I'm really glad you asked the questions --- it helps us make our educational information stronger.
If you are ever in the Philadelphia, PA area, I would love to take you on a tour of our PQI facilities --- we have over 30,000 paint panels on exposure (a few dating back to the '50's) and 1000's with the most recent and forward-looking technologies. In addition, our "farm" contains over 200 different surfaces and substrates (painted/not painted) on exposure as well.
PQI Director of Communications and Alliances
Dow Coating Materials, North America
The Dow Chemical Company