How to Determine Whether the Primer or Bare Metal is Exposed?
4 Answers
Gently touch the scratch with your finger. If there is a noticeable unevenness, it means the damage has reached the primer. If it's not obvious, polishing and waxing can solve the issue. Below is some extended information about car paint: 1. Composition of Car Paint: Generally, a car's paint surface consists of at least four layers, including multi-layer paint, primer, topcoat, and color coat. 2. Paint Colors: The primer can generally be divided into dipping primer, water-based dipping primer, anodic electrophoretic primer, and cathodic electrophoretic primer. Most passenger cars use cathodic electrophoretic primer, which is usually white or gray in color, depending on the vehicle model. For example, black cars typically use white primer, while white cars use gray primer, mainly to make it easier to identify the primer when the paint is scratched.
Hey, I just went through this - my car got scratched by a tree branch with a long mark. When I crouched down to inspect it closely, if the primer is exposed, the color would appear darker or grayish-white compared to the normal paint surface, feeling relatively smooth like a layer of protective coating; whereas exposed metal directly reflects a metallic sheen, feels rough to the touch, and is prone to rust spots. In my case, I noticed brown rust appearing at the scratched area, clearly indicating exposed metal, so it needed immediate treatment to prevent rust from spreading. The standard automotive paint layers from top to bottom are clear coat, base color coat, primer, and beneath that is the metal body, so deeper scratches will reveal different layers. I later bought a touch-up pen to apply a simple coat as a temporary fix, but for serious damage, it's best to visit a professional shop for repainting, otherwise rainwater seepage could easily corrode the body. Regular car washes also help monitor scratch changes for early detection, saving hassle down the line.
When scratches appear on the car, the key to determining whether the primer or the metal is exposed relies on visual inspection and touch. Exposed primer usually appears in a darker color or matte gray, with a relatively smooth surface and no obvious reflection; exposed metal directly reveals the metallic color, which is shiny and may even show rust spots, feeling uneven to the touch. I recommend first cleaning the damaged area and observing the color change in well-lit conditions. If there is rust, it definitely means the metal is exposed, and you should lightly sand it with sandpaper and apply some rust inhibitor for temporary protection. The primer acts as a protective buffer layer for the car body, and if exposed, it may not rust immediately, but leaving it untreated can worsen the condition. Different car models have varying paint thicknesses, so gently testing the depth with a fingernail can also help in judgment—just avoid applying too much force to prevent further damage.
From a car repair perspective, here's how to assess the issue: Exposed primer appears as light gray or dark in color with a smooth, rust-free texture; exposed metal shows direct metallic sheen with high rust risk. The judgment is straightforward: 1. Clean the scratched area to remove dust; 2. Observe the reflection difference under natural daylight - bare metal shines like a mirror; 3. Gently touch with fingers - primer feels smooth, while metal may feel rough or leave rust powder on fingers. 4. Any visible rust confirms exposed metal, requiring sanding and touch-up painting. Primer is an anti-corrosion layer - exposure isn't urgent, but bare metal requires immediate rust prevention. Don't underestimate it - rust spreads into large pits, weakening body strength. When parking, avoid scraping sensitive areas.
