Because it is smooth, slippery and zinc coated, galvanized steel can be difficult to paint. Before taking any chances in this endeavor, remember to prepare the non-stick surface so that it offers adhesion to the paint. Start by cleaning the steel thoroughly with a chemical degreaser. Then clean the outside of the object with white vinegar to lightly scratch it, making it adhere better. It is also very important to sand old steel with a fine sandpaper to remove traces of oxidized zinc, also known as white rust. Finally, apply an all-purpose latex primer to the steel and paint it with two coats of latex paint. Use good quality outdoor products.
Steps
Part 1 of 2: Preparing the steel surface
Step 1. Clean the steel with a degreaser
Spray the solution onto the material and rub with a clean microfiber cloth. A powerful degreaser will thin layers of dirt, grease, mold and other problematic residues without affecting the sensitive zinc coating. Rub the product on small parts of the material until it is completely clean.
- Try using a household cleaner such as a Veja, mineral spirits or chlorine bleach to prepare the steel.
- If you plan to paint a side or roof panel or any other material that is constantly exposed to the elements, it is essential to clean it thoroughly to remove all organic contaminants from the steel.
Step 2. Wait for the material to dry
After you finish cleaning the steel, let it sit until all the degreaser residue has evaporated. This way, you don't run the risk of the solution affecting the action of the vinegar, which serves to roughen the steel.
Leave to prepare and paint the steel indoors, if possible, or wait on a clear day with low humidity
Step 3. Gently sand the steel to remove white rust
When preparing a slightly worn item, you may find a layer of something like dust or chalk on the surface of the material. To remove it, use fine sandpaper (120 or less). Be very patient and rub the sandpaper in a circular motion until the material is even.
- Then wipe the surface with a cloth dampened with warm water to remove dust residue.
- This substance is popularly known as white rust. It forms when the thin zinc coating on steel begins to break down due to weather or exposure to the elements.
Step 4. Clean steel with white vinegar
Moisten a clean, dry cloth with distilled vinegar and wring out the excess. Wipe the cloth all over the steel and replenish the vinegar as necessary. In order for the paint to be uniform, it is essential that the paint catches all corners of the material.
- The acid in the vinegar will slightly scratch the zinc coating, leaving the steel with a rougher, tacky texture.
- Do not let any pieces pass so that the paint does not get stained or peeling.
Step 5. Let the vinegar work for one to two hours
Over that time, the vinegar will corrode the metal's surface. The longer it acts, the more the material will get rough and sticky. If you have time to spare, you can even let the vinegar work overnight.
If you're in a hurry, wait until the steel is dry and move on to primer and paint
Part 2 of 2: Applying Primer and Paint
Step 1. Apply a latex based primer
With a brush or a spray, apply the primer over the entire surface of the steel. Apply it in small parts and try to make the coverage as even as possible. Be careful not to leave any flaws that could cause problems when painting.
- For the primer to last longer, choose a specific product for exteriors.
- If the steel is for industrial use or for extreme conditions, try changing the primer for a high-performance epoxy one. Epoxy primers are semi-permanent, scratch resistant and do not peel easily.
Step 2. Allow the primer to dry completely
This can take between two to six hours, depending on the product chosen. To see if the surface is ready to be painted, run your finger across it. If it's still sticky, let it dry a little longer.
The wet primer will hinder the adhesion of the paint to the steel
Step 3. Choose the right ink
In most cases, a common latex exterior paint should do the trick. Take a look at a building supply store. Avoid using alkyd paints, such as spray paints, on galvanized steel.
- For best results, look for a paint specifically designed for galvanized steel.
- The enamels present in alkyd paints can react in contact with the zinc coating, leading to poor adhesion and peeling.
Step 4. Prime the coat
Spread paint over the entire surface with long, linear strokes. With the tip of the brush, paint the reliefs, indentations and other textured parts of the steel well. Take a look to see if you haven't missed any pieces before continuing.
If you plan to paint a large surface, such as a side or roof panel, use a paint roller
Step 5. Wait for the first coat of paint to dry before applying the second coat
This usually takes between three and four hours. In the meantime, avoid touching the fresh paint so as not to leave any stain or wrinkle in the paint.
Drying time will be longer if the weather is hot and humid
Step 6. Apply a second coat of paint
In most cases, two coats are more than enough. Apply the top layer in the same way as the first. Take it easy to make sure you don't leave any flaws behind. Imperfections will be visible after the paint dries.
- Indirect airflow from a floor fan or air conditioner can help paint dry faster.
- After the paint dries, install or start using the painted part.
Step 7. Limit the ink exposure time while waiting for it to cure
Although most latex-based paints dry in a matter of hours, the product can take a few weeks (or in some cases up to a month) to fully set. Avoid exposing the steel to pressures that could damage it, rain or drastic changes in temperature. After the ink cures, the material is ready to take on anything.
As long as you apply it correctly, the ink will last a long time and withstand extreme conditions
Tips
- Protect yourself with disposable rubber gloves so substances such as cleaners and ink don't get on your hands.
- Painting a piece of galvanized steel is a quick and inexpensive little job anyone can do. It just requires a little paint and primer and a few hours of work, most of which you'll spend waiting for the paint to dry.
- Galvanized steel is sometimes treated with a type of product called a passivator, which protects the material from corrosion. However, this can make painting more complicated. To see if your item is coated with a passivator, sand a small hidden piece of steel and apply a dab of water-diluted copper sulfate to the surrounding area. If the two parts darken at different speeds, the steel has probably been coated with a passivator and you won't be able to paint it without special treatment.