Because it has a smooth, slippery surface and is zinc/zinc coated, galvanized steel can be difficult to paint. Before starting, the steel surface needs to be prepared so that the paint can adhere. Start by cleaning all the steel using a chemical degreaser. Once done, wipe the exterior with white vinegar to lightly etch the surface and make it easier for the paint to adhere; also make sure you scrub the surface of the steel with sandpaper to remove any residual oxidized zinc (also known as “white rust”). Finally apply an outdoor latex primer to the steel, then finish with two coats of exterior latex paint.
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Part 1 of 2: Preparing the Steel Surface
Step 1. Clean the steel with a chemical degreaser
Spray the surface with the solution, then buff with a clean, lint-free cloth. The powerful degreaser will penetrate dirt, oil, mold and other problematic residues without affecting the temperamental zinc coating. Continue in small sections until all steel surfaces are clean.
- Common household products such as mineral spirits and chlorine bleach can be used to prepare galvanized steel.
- If you are trying to paint the side panels, roof flashing, or other material exposed to the elements, perform a thorough cleaning to remove organic contaminants from the outer surface of the steel.
Step 2. Allow the steel surface to dry
If the steel has been cleaned, wait until all traces of the degreaser have evaporated. This way, the degreaser will not interfere with the work of the vinegar, which will be used to roughen the steel surface.
If possible, the preparation and painting of steel should be carried out on a sunny, non-humid day
Step 3. Rub the galvanized steel lightly to remove white rust
For worn objects, there is usually a layer of chalk or powder on the surface. This layer can be removed easily using a large grit (roughness) sandpaper (preferably 120 grit) and a little patience. Rub the steel in a circular motion until the surface looks uniform.
- After that, wipe the surface with a cloth dampened in warm water to remove dust.
- This lime is known as white rust. This rust forms when the zinc coating on steel begins to break down due to age or exposure to various elements.
Step 4. Wipe the steel with white vinegar
Wet a clean, dry cloth with distilled white vinegar and wring it out until it doesn't drip. Wipe the galvanized steel thoroughly, and add vinegar if needed. For the paint to work evenly, the vinegar must touch every part of the exterior.
- The acid in the vinegar will etch the slick zinc coating, giving it a rougher texture and better adhesion to the paint.
- If you miss a certain part, the paint may smudge or peel off.
Step 5. Leave the vinegar for 1-2 hours
This time allows the vinegar to eat up the galvanizing surface. The longer it is left on, the more pronounced the effect of the etching will be, and the paint will adhere better. If possible, let it sit overnight.
If there's not enough time, wait until the surface is dry and touchable before moving on to the primer and paint process
Part 2 of 2: Applying Primer and Paint
Step 1. Apply a latex-based primer
Wipe or spray the primer onto the prepared steel surface. Work in small sections so that the results are even. Make sure there are no missing or too thin sections that could cause problems later.
- For maximum durability and adhesion, choose a versatile latex primer designed for the outdoors.
- If the steel is made for harsh industrial or outdoor conditions, it's best to choose an epoxy primer of higher quality. Epoxy primers provide semi-permanent adhesion, and are resistant to scratches, nicks, and peels.
Step 2. Allow the primer to dry completely
Usually it takes up to 2-6 hours, depending on the product used. To test whether the primer is paintable, wipe the surface with your finger. If it still feels sticky, you may need to wait a little longer.
If you paint on a wet primer, the stickiness will decrease
Step 3. Choose the right paint
In most cases, standard latex paint designed for the outdoors will suffice. You can buy it at a paint or hardware store. Avoid using alkyd based paints (eg spray paint) on galvanized steel.
- For the best results, look for paints specifically designed for galvanizing steel.
- The enamel in alkyd paints can react with a thin layer of zinc on the surface of the galvanizing steel, causing the paint to not adhere well and peel.
Step 4. Wipe off the first coat of paint
Apply paint over the entire steel surface in long, straight strokes. Use the tip of the brush to reach recesses, holes, and textured areas. Check to make sure there are no gaps or parts left behind before proceeding.
You can use rollers to paint large surfaces such as side panels or roofs
Step 5. Allow the base coat to dry and touch
It usually takes 3-4 hours before the second coat can be painted. Meanwhile, do not touch the wet paint so as not to leave streaks or blemishes on the finished product.
Expect longer paint dry times in warm, humid conditions
Step 6. Continue with the second and final coat of paint
Two layers are usually sufficient for most projects. Apply the next coat of paint like the first coat. Take the time to make sure there are no defects in your work; all errors will appear when the paint is dry.
- Indirect airflow from fans or air conditioners can help paint dry faster.
- If the outer layer of paint is dry, please install or place the steel according to its use.
Step 7. Limit paint exposure as it hardens
While most latex paints dry in a matter of hours, it can take several weeks (or in some cases up to a month) to fully harden. If possible, protect the steel from stress and wear, such as from pressure, heavy precipitation, or drastic temperature changes until the paint has fully hardened. When it's hard, the paint can withstand anything that hits it.
If used properly, paint on galvanized steel will last a long time and withstand extreme conditions
Tips
- Wear disposable gloves to prevent hands from being exposed to chemical cleaners and latex paint while working.
- Painting galvanized steel is a quick and inexpensive project that anyone can undertake; You only need paint and primer, and a few hours, mostly waiting for the paint or primer to dry.
- Galvanized steel surfaces are sometimes treated with chemicals called passivators, which protect the exterior from corrosion but can complicate painting. To test for the presence of a passivator, sand the steel in an inconspicuous area and rub it with copper sulfate diluted with water. If the two darken at different speeds, it is likely that the passivation has been applied to the steel, and cannot be painted before special weathering.
