Hey there, folks! If you’re in the powder coating game, you know pinholing is that annoying, tiny nightmare that pops up out of nowhere—ruining a perfect finish, wasting material, and turning a smooth part into something you’d be embarrassed to ship to a client. As a powder coating supplier who’s been in this space for over a decade, I’ve seen way too many jobs get held back by this dumb little issue, and I’m here to break down exactly how to prevent it, no fancy jargon required. Powder Coating
First, let’s get on the same page: what even is pinholing? It’s those small, shallow holes (usually 0.1 to 1mm wide) that form in the cured powder coat, like someone poked the finish with a needle. Most of the time, it’s caused by trapped air, moisture, or solvents trying to escape while the powder melts and flows during curing. Think of it like baking a cake and leaving air bubbles in the batter—they pop when the cake bakes, leaving tiny holes. But the good news? 90% of the time, this is totally avoidable if you nail the prep, the powder you pick, and your oven process.
Let’s start with prep, because I can’t stress this enough—bad prep is the #1 culprit I see when customers come to me with pinholing problems. A lot of folks skip over small steps here, and that’s where issues creep in. First, your part’s surface: if there’s any grease, oil, or even residual cutting fluid on metal, that’s going to burn off during curing, right? But when it does, it turns into a gas that gets trapped under the melting powder, leaving a hole. I always tell new customers: even if a part looks “clean,” wipe it down with a wax and grease remover (not just acetone, which can leave a weird residue if you don’t let it evaporate fully) before anything else. That 2-minute step saves you hours of rework later.
Then there’s drying after prep. Wet pre-treatment (like phosphating or conversion coating) needs to be 100% dry before you apply powder. I’ve had customers cut corners here, air-dry parts for 10 minutes, then wonder why pinholing pops up. Any leftover water on the part will turn to steam in the curing oven, and that steam escapes through the melting powder, leaving holes. I recommend using a hot air blow-off or a low-temp oven bake (around 120°F/49°C for 10 mins) to make sure every last drop is gone. Even if you’re in a humid area, bump that bake time by 5 minutes—humidity in the air can stick to the part’s surface, so don’t skip that.
Next up: the powder itself. Not all powders are created equal, and some are way more prone to pinholing than others. For example, some low-quality, cheap bulk powders have too many volatile organic compounds (VOCs) that evaporate when heated. Those VOCs don’t always escape fully before the powder cures, so they get trapped and form holes. That’s why as a supplier, I don’t just push the cheapest stuff— I match powder to your job. If you’re coating thick parts or parts that hold a lot of moisture, we’ll recommend a powder with better flow characteristics, or one formulated to outgas during curing. Also, don’t forget to store your powder correctly! If you leave powder bins in a damp garage or warehouse, moisture gets trapped in the powder particles. When you apply it, that moisture turns to steam in the oven, and boom—pinholes. We always tell customers to store powder in a cool, dry space, and never use powder that’s past its expiration date. Old powder clumps up, and those clumps can trap air when you spray them, leading to holes in the finish.
Now, the application process. A lot of people focus on the gun settings, but even small things like gun distance and spray pattern matter for pinholing. If you hold your spray gun too close to the part, you’re applying powder too thick in spots. Thick powder takes longer to melt, so any trapped air or moisture has a harder time escaping before the surface cures. Aim for a consistent thickness—usually 1.5 to 2 mils for most jobs. Too thin, and you’re just asking for defects, too thick, and pinholing is almost guaranteed. Also, make sure your ground is good. Poor grounding means the powder doesn’t adhere evenly, and you might end up with thin spots where air can get trapped and form holes. I always remind customers to check their grounding clamps, clean them regularly, and make sure they’re attached directly to the part (not to a rack that’s dirty or rusty).
Then there’s the oven curing step—this is where a lot of mistakes happen, especially with temperature and air flow. First, don’t rush the cure cycle. A lot of shops crank up the oven temp to get parts done faster, but too high a temp can make the surface of the powder cure before the trapped air or moisture can escape. That’s called “skinning over”—the top layer hardens, and whatever’s underneath has nowhere to go, so it blows holes through the finish. Instead, follow the powder manufacturer’s cure schedule exactly. For most powders, that’s 300°F (149°C) for 15-20 minutes, but some low-temp powders need a little longer flow time. Also, air flow in the oven is non-negotiable. Stagnant air means fumes and moisture can’t escape from the oven chamber, so they get trapped in the curing part, leading to pinholing. I always tell customers to make sure their oven has proper exhaust ventilation—around 5-10 air changes per hour, depending on the size. If you’re curing big batches, don’t overload the oven! Stacking parts too close blocks air flow around each part, so the air on the inside of the stack can’t escape, leading to defects.
Wait, let’s talk about a common trick some pros use to spot pinholing before it’s too late. If you’re unsure, do a test cure with a spare part. Apply powder to a small piece of scrap metal from the same batch, cure it, and inspect it closely. If you see any pinholes, you can adjust your prep, powder, or oven settings before wasting a whole batch of good parts. That’s a step I swear by—saving a few minutes on a test saves you hours of rework later.
I’ve also had customers come to me with pinholing that was random—one part is fine, the next one has holes, no idea why. Most of the time, that’s because of a tiny, easy-to-miss variable: dust in the air around your spray booth. If your booth has floating dust, that dust can get trapped in the powder layer, and when it burns off in the oven, it leaves a pinhole. So make sure your booth is clean—wipe down the walls regularly, change your filters on schedule, and if you’re in a dusty area, maybe use a HEPA filter in your spray area. That’s a small thing, but it makes a big difference for consistent finishes.
Let me give you an example: last quarter, a local automotive shop was coming to me with 1 out of every 10 custom wheel sets having pinholing. They’d tried everything—prep, powder brand, oven temp—nothing worked. Turns out, their conversion coating process was leaving tiny amounts of water trapped in the wheel’s crevices, and they were air-drying them instead of baking. We recommended a 10-minute bake at 140°F (60°C) after conversion coating, and switched them to a powder with better outgassing properties. They haven’t had a pinholing issue since. That’s why I don’t just sell powder—I work with my customers to figure out their specific problem, because every shop’s setup is a little different.
At the end of the day, pinholing isn’t a random flaw—it’s a sign something is off in one of those three areas: prep, powder, or process. If you’re dealing with consistent pinholing and none of these tips are fixing it, don’t guess or waste time on trial and error. As your powder coating supplier, I can help you troubleshoot—whether that’s testing a different powder formulation, tweaking your prep steps, or adjusting your oven’s air flow. We’ve got a team of pros who have seen every pinholing scenario under the sun, and we can get your process back on track.
Whether you’re a small job shop or a big manufacturing operation, getting a smooth, pinhole-free finish is what keeps your customers coming back. Don’t let those tiny holes derail your hard work. If you’re ready to test better powder solutions or troubleshoot your current pinholing issues, reach out to our team today to connect for a consultation. We’re here to help you get the job done right, no headaches required.
Cylinder Accessories References
- Technical Bulletin: Pinholing in Powder Coatings, Powder Coating Manufacturers Association, 2022.
- Powder Coating Application Guidelines, American Coatings Association, 2021.
- Troubleshooting Common Powder Coating Defects, Surface Technology Magazine, Vol. 18, No. 3, 2023.
Shanghai Luzhen SCM Co., Ltd.
As one of the most professional powder coating manufacturers and suppliers in China, we’re featured by quality products and good price. Please rest assured to buy bulk discount powder coating from our factory. We also accept customized orders.
Address:
E-mail: bao@lu-chain.com
WebSite: https://www.lu-chain.com/
