Aluminum Siding – Paint 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 & Exterior Painting Tips
OK, let's get the show on the road. We want to paint your aluminum siding. The first thing we are going to do is thoroughly wash the siding. What, go to the tool rental shop? Get a pressure washer? Hmmmmmmmm, let's think about this.
Pressure washers are great when used in the hands of someone who knows how to use them. However, with aluminum siding you can have some problems. For example, if you direct the spray near the ends of pieces at doors and windows, you can create leaks into your home. If you direct the spray at a seam overlap, water can get behind the siding. Also, pressure washing doesn't always get all of the dirt off. If you direct the spray at a downward angle, the area just under the beveled bump-out doesn't even get cleaned!
A better alternative, although more work, is old fashioned elbow grease. Using a large sponge, soapy water, and a scrub brush, you can do a great job.
Start cleaning at the top of the siding and work down. Rinse the cleaned siding until the water runs clear. You want to remove as much old pigment as possible. Even after the siding dries, there is a possibility that a small amount of pigment or chalk will get on your fingers. That's OK.
Primer - A Must
As we discussed earlier, you must apply an oil based metal primer to seal any oxidized aluminum. Try to use a primer that is close in color to your finish paint. You can get primers tinted! Tint it 1/2 or 3/4 strength of what the finish color is supposed to be. Don't forget to thin the primer: 1 pint of thinner to 1 gallon of paint.
Apply the primer after the siding is completely dry. Don't prime too much siding! The freshly primed siding should not be allowed to weather. Ideally you should paint the primed siding the next day. So, don't prime for one week and then paint the next!
Applying the Finish Coat
It's now time for the glory work. This is what everyone wants to do right away. They are impatient. They want instant gratification. Great things come to those who wait! Finish painting of aluminum siding is critical. The weather can ruin your job! No, I don't mean rain. Sun and wind are your enemies! These two adversaries will cause the paint to dry too rapidly. The paint will not have a chance to get a good grip on the primer. The sun can actually boil the water beneath the outer paint skin and cause blisters! It has happened to me. The old saying is follow the sun. This means try to paint in the shade. Let the sun hit a wall and paint it after it is gone or high in the sky. Paint north facing walls on sunny days and south facing walls on overcast days. Cool, overcast days are ideal for painting aluminum siding. These days are easy on the paint and your body. Wait for a good day and you may squeeze an extra 5 years from the job!
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 waterbased 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