How to Spray Paint Metal: Techshield Aerosol Primer, Topcoat and Lacquer
Not every job needs a spray gun and a tin of 2-pack. Brackets, suspension parts, trim, small repairs, trailer fittings and garden gates can all be finished properly from a spray can, as long as you use the right primer, build up light coats and give each one time to flash off. Rustbuster’s Techshield aerosols give you a complete system in 500ml cans: two primers, three black topcoats and a clear lacquer. This guide shows you which one to use and how to get a finish that lasts.
The Techshield aerosol range
| Aerosol | What it’s for | Key facts |
|---|---|---|
| Zinc Rich Weldable Primer | Cathodic protection for bare or galvanised steel, joints and repairs | 90% zinc in the dry film, 1000-hour salt spray, heat resistant to 350°C, matches old galvanising |
| Primer Grey | General-purpose primer and filler under the topcoat | Sandable in 15 minutes; sticks to metal, aluminium, wood and more |
| Gloss Black | High-shine black topcoat | Weather- and UV-resistant, scratch and impact resistant, can be machine-polished; indoor and outdoor use |
| Satin Black | Factory-look semi-gloss black topcoat | |
| Matt Black | Flat black topcoat | |
| Clear Lacquer | Clear protective topcoat | UV- and weather-resistant, hard-wearing, polishable |
The range also includes Underbody Schutz and Cavity Wax aerosols. They’re underbody protection rather than paint, so they’re covered in our Techshield underseal and cavity wax guide.
Step 1: choose your primer
Every Techshield topcoat needs a primer underneath, and choosing the right one makes the biggest difference to how long the finish lasts.
| Zinc Rich Weldable Primer | Primer Grey | |
|---|---|---|
| Best for | Bare steel, galvanised steel, weld joints, chassis and repairs where rust protection matters most | General priming and filling under a topcoat, including aluminium and wood |
| How it protects | Zinc protects the steel cathodically, just like galvanising | A barrier coat that fills and gives the topcoat good adhesion |
| Binder | Epoxy-ester | Nitro combi |
| Drying at 20°C | Touch-dry 10–15 min, handle 20–30 min, re-coat within 30 min | Touch-dry 10–20 min, sand after 15 min, overcoat after 15–30 min |
| Coverage | 1.5–2m² per can | About 1.5–2.2m² per can |
For the most important steel parts, use zinc for protection. If you need to fill small marks before the topcoat, Primer Grey is easy to sand.
Step 2: choose your finish
- Gloss Black: a deep shine for show parts, brackets and anything you want to stand out.
- Satin Black: the classic factory finish for chassis parts, suspension, wheels and trim. It also hides small imperfections better than gloss.
- Matt Black: a flat, modern look for trim, engine-bay brackets and detail parts.
- Clear Lacquer: an optional clear topcoat that adds UV, weather and scratch resistance, and can be polished.
How to spray paint metal with Techshield aerosols
De-rust, abrade and degrease
The surface must be free from rust, grease and moisture. Remove rust mechanically or with Phos-Kleen A, sand the surface lightly to give it a key, then degrease with Safer Degreaser and let it dry completely.
Mask off and warm the can
Mask anything you don’t want painted. Work somewhere dry, warm and well ventilated, with the can at room temperature: cold cans and damp air give a rough, dull finish.
Shake it properly
Once the agitator ball rattles freely, keep shaking for at least two more minutes, and shake again regularly while you spray.
Prime in light coats
Hold the can about 25cm from the surface. Start spraying just off the part and move across it in smooth, overlapping passes. Apply several light coats, leaving 5–10 minutes between each to flash off. Light coats don’t run.
Flat and topcoat
Lightly flat Primer Grey once it’s sandable (about 15 minutes) and wipe off the dust. Apply the black topcoat in the same way: several light coats, building up to full colour.
Lacquer if you want extra protection
The topcoats can be overcoated after 2 hours. Add Clear Lacquer in light coats for extra UV and scratch resistance.
Clear the nozzle
When you’ve finished, turn the can upside down and spray for 2–3 seconds until only gas comes out, so the valve doesn’t block before next time.
Drying times at a glance (20°C)
| Aerosol | Dust-free | Touch-dry | Overcoat |
|---|---|---|---|
| Zinc Rich Weldable Primer | – | 10–15 min | Within 30 min (handle after 20–30 min) |
| Primer Grey | 5–10 min | 10–20 min | 15–30 min (sand after 15 min) |
| Gloss, Satin, Matt Black | 5–10 min | 10–20 min | After 2 hours |
| Clear Lacquer | 5–10 min | 10–20 min | After 2 hours |
Drying times depend on temperature, humidity and coat thickness, so allow longer in a cold or damp garage.
Mistakes to avoid
- Spraying over rust or grease. Paint won’t stick to contamination, and rust carries on underneath.
- Skipping the primer. Topcoats are designed to go over a primer, not straight onto bare metal.
- One heavy coat. It runs, sags and takes much longer to dry. Several light coats give a better finish.
- Spraying too close. Keep about 25cm away and keep the can moving.
- Painting in the cold or damp. It causes a cloudy, rough finish. Warm the can and the part first.
- Not clearing the nozzle. Invert the can for a few seconds after use, or it’ll be blocked next time.
Techshield aerosol FAQs
Do I need a primer before spray painting metal?
Yes. Techshield topcoats are designed to go over a suitable primer. On bare or galvanised steel, use Techshield Zinc Rich Weldable Primer for the best rust protection, or Primer Grey for general priming and filling.
What’s the difference between zinc primer and grey primer?
Zinc Rich Weldable Primer contains 90% zinc in the dry film and protects steel cathodically, like galvanising, with 1000-hour salt-spray resistance and heat resistance to 350°C. Primer Grey is a fast-drying, easily sanded primer and filler that gives the topcoat excellent adhesion on metal, aluminium, wood and other surfaces.
How long should I leave between coats?
Allow 5–10 minutes between light coats to flash off. Primer Grey can be overcoated after 15–30 minutes, Zinc Rich Weldable Primer should be re-coated within 30 minutes, and the black topcoats and Clear Lacquer can be overcoated after 2 hours at 20°C.
Can I put black topcoat over the zinc primer?
Yes. Rustbuster state that Techshield Zinc Rich Weldable Primer can be overcoated with a suitable topcoat such as Techshield Gloss, Satin or Matt Black.
How much will one can cover?
Each 500ml can covers roughly 1.5–2.2m² per coat, depending on the surface and how thickly it’s applied. Allow for several light coats when you work out how many cans you need.
Do I need clear lacquer over black paint?
It’s optional. The black topcoats are already weather-, UV- and scratch-resistant. Clear Lacquer adds an extra hard-wearing, polishable layer for parts that take a lot of handling or weather.
More rust guides: surface preparation, how to paint galvanised steel, stonechip and seam sealing and Techshield underseal and cavity wax.
