How to paint galvanized steel and profiled sheet: the key is not the paint but the primer. Paint is never applied straight onto zinc, because it does not hold there. Galvanized steel is degreased and given 1 coat of alkyd primer DEKOMAL GF-021 or EXTRAMAL GF-021, and only once the primer is dry is it painted with RUBBER FARBA rubber paint, PF-115 alkyd enamel or DEKOLUX enamel. Below: which primer to choose, how to prepare the sheet and what to paint on top.
Why paint does not hold on bare zinc
The zinc layer is smooth and dense. Paint applied directly has nothing to grip and peels off in sheets within a season or two. GF-021 primer acts as the intermediate layer: according to its data sheet it improves adhesion of the topcoat and adds corrosion protection. So the system for galvanized steel is always the same:
- degreasing;
- DEKOMAL or EXTRAMAL GF-021 primer, 1 coat;
- once the primer is fully dry, the topcoat: RUBBER FARBA, PF-115 or DEKOLUX.
ZAHYST 3 in 1 primer-enamel is not suitable for galvanized steel, either as a primer or as a finish: it is made for ferrous metal.
GF-021 primer: DEKOMAL or EXTRAMAL
Both are alkyd anti-corrosion primers for metal. According to their data sheets, systems built on them work outdoors and indoors and withstand urban and industrial atmospheres, and the primer itself reduces topcoat consumption. They differ in drying time, consumption and colours.
Parameter | DEKOMAL GF-021 | EXTRAMAL GF-021 |
|---|---|---|
Consumption per coat | 60–100 g/m² | 80–120 g/m² |
Drying | 6 hours | 12 hours |
Colours | white, grey, red-brown, black | grey, red-brown |
Pack sizes | 0.9; 2.7; 22 kg | 0.9; 2.8; 22 kg |
Thinner | white spirit, solvent naphtha or a 1:1 mix, up to 10% | |
Application conditions | air and surface +5…+30 °C, humidity up to 60%; optimum +18…+25 °C | |
DEKOMAL dries twice as fast, so you can prime in one day and paint the next. Under a light topcoat, a white or grey primer is the easier choice.
Preparing galvanized steel and profiled sheet
- Remove any old coating that is flaking. Leave sound coating in place but sand it.
- Wash off dirt and dust.
- Degrease the metal. ROZCHYNNYK 3 in 1 organic solvent works for this: apply it with a rag soaked in solvent. Ventilate and wear gloves.
- Sand glossy areas matt and let the surface dry completely.
If rust has appeared on galvanized steel
Red rust on an old sheet means the zinc no longer protects the steel at that spot. Remove the rust down to sound metal and, as the GF-021 data sheet requires, prime straight after cleaning, before fresh rust forms.
Profiled sheet with a factory polymer coating
Polymer coatings (polyester, Pural and others) are not named separately in the data sheets. Treat such sheet as a sound old coating: wash, degrease and sand off the gloss. Before painting a whole roof or fence, do a test patch and check adhesion once dry: cut a grid into the film, press tape on and pull it off sharply. If the coating comes off in squares, do not use it on that sheet.
How to prime galvanized steel with GF-021
- Stir the primer thoroughly in the tin.
- If needed, thin with white spirit or solvent naphtha, by no more than 10%.
- Apply 1 coat by roller, brush or spray, evenly and without gaps on the corrugations and sheet edges.
- Work at +5…+30 °C and humidity up to 60%. Cold and high humidity slow drying.
- Let the primer dry fully: DEKOMAL 6 hours, EXTRAMAL 12 hours. Under PF-115 enamel, leave the primer at least 24 hours.
- Clean tools with solvent naphtha.
What to paint over the primer
Topcoat | When to use | Coats |
|---|---|---|
roofs, fences and gutters made of profiled sheet: the film is elastic and moves with the metal in sun and frost | 2–3 coats, 100–200 g/m² per coat | |
classic gloss finish for gates, railings and structures | per the enamel data sheet | |
alkyd-urethane enamel when a high gloss is needed | per the enamel data sheet |
RUBBER FARBA is water-based: apply it at +10…+30 °C air temperature and humidity below 80%, thin with water by no more than 10%; each coat dries in up to 2 hours at +23 °C. More about it in the article what rubber paint is, and the full roof process is in how to paint a roof.
How much material you need
Corrugations add area, so measure the sheet along its profile. For 50 m², one coat takes 3–5 kg of DEKOMAL GF-021 or 4–6 kg of EXTRAMAL GF-021. On top, 10–20 kg of RUBBER FARBA for two coats. Work out your own figures with the primer consumption calculator and the paint consumption calculator.
Ferrous metal next to galvanized steel
Parts made of ferrous metal without zinc, such as steel posts or a gate frame, can be primed with the same GF-021 and painted together with the sheet. Another option for them is ZAHYST 3 in 1 as a standalone coating straight over rust, with no primer. Galvanized sheet is not painted with it. More on the primer-enamel in how to apply 3-in-1 paint over rust, and on steel gates in how to paint metal gates so they do not rust.
Common mistakes
- Painting galvanized steel without GF-021 primer.
- Using ZAHYST 3 in 1 on galvanized steel.
- Skipping degreasing: neither primer nor paint holds on a greasy film.
- Painting over primer that is not fully dry.
- Priming in damp weather: air humidity must be 60% or lower.
- Thinning primer or paint by more than 10%.
What to buy
For galvanized steel, profiled sheet and metal gutters: ROZCHYNNYK 3 in 1 for degreasing, DEKOMAL or EXTRAMAL GF-021 primer in 1 coat, and on top RUBBER FARBA, PF-115 enamel or DEKOLUX.
FAQ
What do you prime galvanized steel with?
DEKOMAL GF-021 or EXTRAMAL GF-021 alkyd primer, 1 coat after degreasing. Other primers and ZAHYST 3 in 1 are not used on galvanized steel.
Can galvanized steel be painted without primer?
No. Neither rubber paint nor alkyd enamels go directly onto zinc: without GF-021 primer the coating peels.
How long does GF-021 dry before painting?
DEKOMAL GF-021 takes 6 hours and EXTRAMAL GF-021 12 hours under normal conditions. Under PF-115 enamel, leave the primer at least 24 hours.
Can galvanized steel be painted with alkyd enamel?
Yes, over GF-021 primer: with PF-115 enamel or DEKOLUX.
What do you degrease galvanized steel with before priming?
ROZCHYNNYK 3 in 1 organic solvent, applied with a rag soaked in it. Let the surface dry after degreasing.
Can profiled sheet with a polymer coating be painted?
Polymer coatings are not named separately in the data sheets. Sand off the gloss, degrease, and paint a test patch first, checking adhesion with tape.
