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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14 comments:

Donna said...

Hey Bill, I added you to my Google reader. You can thank that JoCo SOB. I'm way out here in Lafayette County.

Bill the Painter said...

Thanks for reading! I hope to update a little more frequently than I have in the past. Take care!

Bill

Anonymous said...

Bill,
What if your steel siding is chalking and rusting? Do you take additional steps in the prep work for the rust spots?

Bill the Painter said...

Most steel siding is chalking pretty bad when it's ready for painting. By scrubbing and rinsing with a power washer you should get most of the chalk removed. If there is still a lot of chalk, repeat the process. You will NEVER be able to remove all of the chalk. Once you get the siding as clean as you can, use an Acrylic Bonding Primer to seal all of the siding. This primer "sticks" really well to chalky surfaces!

For rust, I typically use a Rust-Oleum type primer. That's the best you can do. If the siding is rusting from the inside out, you may have to prime again as the rust comes through. It may never stop coming back until the water is kept out. I hope this helps!

Christine Rizzo said...

This was superhelpful. Thank you. Another had recommeneded oil base paints to repaint metal siding...you recommend acrylic. What are the major advantages of one over the other. Thank you again.

Bill the Painter said...

Whatever you do, DO NOT use an oil based paint! I doubt you'll be able to find one in the first place, without going to a commercial grade paint.

Oil-based paints dry hard and are inflexible. Your siding will expand and contract with the temperature. The oil based paint will eventually crack, allowing moisture behind it and eventually will peel off. They will also chalk and fade much faster than Latex paint, resulting in a shorter lifespan.

100% Acrylic Latex Paints are flexible! They will expand an contract with your siding. In addition, they will retain their color a lot longer and any oil-based paint.

When buying your paint, make sure you choose a high quality 100% Acrylic Latex. Don't buy a paint that brags that it is "Primer and Paint all in one" Unless you want to throw away your money, avoid pants with "Lifetime Warranties" For most people, they are a total waste of money!

Remember, no matter what paint you choose, it will fail if you don't do the proper prep! NO warranty covers that!

Good luck!

Bill the Painter said...

Whatever you do, DO NOT use an oil based paint! I doubt you'll be able to find one in the first place, without going to a commercial grade paint.

Oil-based paints dry hard and are inflexible. Your siding will expand and contract with the temperature. The oil based paint will eventually crack, allowing moisture behind it and eventually will peel off. They will also chalk and fade much faster than Latex paint, resulting in a shorter lifespan.

100% Acrylic Latex Paints are flexible! They will expand an contract with your siding. In addition, they will retain their color a lot longer and any oil-based paint.

When buying your paint, make sure you choose a high quality 100% Acrylic Latex. Don't buy a paint that brags that it is "Primer and Paint all in one" Unless you want to throw away your money, avoid pants with "Lifetime Warranties" For most people, they are a total waste of money!

Remember, no matter what paint you choose, it will fail if you don't do the proper prep! NO warranty covers that!

Good luck!

Travis said...

We have steel siding (magnets stick to it) on our house and we are getting ready to paint. It looks similar to the photo you posted. The paint was peeling badly and I power washed a majority of it off down to the bare metal. Some of the old paint remained in place. Would the acrylic bonding primer be the way to go with bare metal in some spots and old painted metal in others? Also, should I assume it's galvanized? Perhaps that doesn't change anything. By the way you have the best information on the web for this topic. Any help is appreciated. Thanks!

Unknown said...

Bill, A lot of sites and reputable paint stores recommend a solvent based primer for aluminum siding and then 100% acryllic latex for the top coats. Can you elaborate.

Thanks, Mark in Seattle

Bill the Painter said...

I'm sure there are some solvent based primers that will work, but my experience had been with the acrylic bonding primers. I KNOW it works!

Regardless of the primer you decide to use, it is VERY important to make sure you have a clean, chalk free surface to apply it to. You aren't going to get ALL of it, but get as much as you can.

On the home at the beginning of this post, we primed the ENTIRE exterior with the acrylic bonding primer. This helps your topcoat stick to both the bare steel and remaining painted steel, while covering the entire surface with a similar colored base coat. This primer is "extra sticky" (a technical term) and provides a great surface to apply a topcoat to.

Again, there are many primer options, but when I have success with a process, I don't second guess the process and the products involved.

I hope this helps!

Anonymous said...

Bill, I work for a national paint company and I wish I could have you explain all of this about prep work and warranties to my customers. Excellent site with solid information. Thanks for this blog.

Penelope Justice said...

I have exterior windows with an aluminum trim. These have been pressure washed and most of old paint is gone, surface is clean, and bare aluminum is showing. I was going to prime with Rustoleum's oil based primer and the paint with a good acrylic latex. Does this sound good to you? Thanks for your advice.
Penny

Bill the Painter said...

Penny,

I don't believe an oil-based primer is really necessary in your case. Oil-based primer is best used on wood surfaces where it can soak in and protect it.

You'll have excellent results with a clean surface and the acrylic bonding primer.

Good luck!

The Mob said...

Thank you for the great info.