Wednesday, May 13, 2009

Steel or Aluminum Siding Painting

Question: I have a problem with painting the metal siding on my shed. I painted it with Rust-Oleum glossy white, but when the weather gets really cold, the paint pops off in large sections. What is my problem? Should I be using a different kind of paint?

Thanks for the question! Sometimes painting exterior metal can be tricky, whether it’s a shed or metal siding. Preparation work is different for metal than it is for wood. I can’t tell from your description, but I am going to assume when the paint peels off, the primer comes with it. I’ll bet it either peels down to the bare metal or the original finish. Getting the surface clean is really the key here. If you have bare metal, it’s probably galvanized steel. It’s best to scrub the metal with a really good cleaning solution. The best is called Tri Sodium Phosphate (TSP). It’s a powder that is available at most box stores or paint stores. You mix it with water, scrub down the areas to be painted with a stiff bristled brush and rinse it all clean.

Here is a picture of a project we did last year. The home has insulated steel siding, but the original paint finish was severely worn. This was taken right after the home was power washed and scrubbed to remove the chalking, which was pretty extensive.

This method also works great for painted aluminum siding. The big test is very simple: wipe your hand across the surface and look for a chalky white residue. Coincidentally this is called “chalking.” This is how a paint finish wears out and ages. It’s perfectly normal. You MUST remove all of this chalking! If you don’t, the new paint you put on will come right back off.

After you have removed all of the chalking, you should prime everything with an Acrylic Bonding Primer. Most paint stores carry have one. This primer will “grab on” to the metal better than most other primers. It also gives you an excellent base for your new paint. After you have everything primed, you can apply 1-2 coats of your favorite 100% Acrylic exterior paint.

Here is a picture that was taken shortly after the home was painted. It now has a sound finish that will last for years to come. The front of the house faces South, on a sunny day, the brightness of the white will definitely cause you to shield your eyes!

Be careful not to go too dark on your colors. Sheet metal can expand and contract quite a bit with the temperature. Darker colors absorb more light and may cause more heat, causing more expansion than normal. Paint will stretch, but it has its limits! Stay with lighter colors that reflect more light and will keep everything cooler. Your best bet is to go back with the same color as the original.

Thanks for the question!

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