How to Prevent Powder from Clumping or "Spitting"
If you’ve ever been mid-spray and your gun suddenly spits powder like a pepper shaker, you know how frustrating (and costly) it can be. Learning how to prevent powder coating clumping is crucial, as I’ve seen it happen in one-man shops and high-volume lines, the end result is the same: wasted powder, extra labor, and a finish that looks like it’s been through a sandstorm.
Here’s the truth: powder doesn’t clump or spit “just because.” There’s always a cause, and once you know it, you can stop it in its tracks.
1. Moisture Is the Silent Killer
Powder coating powder is hygroscopic, it absorbs moisture from the air. If that moisture makes it into your hopper, it binds the powder together into little pellets that refuse to fluidize.
Why it happens:
Humid shop conditions
Leaky or undersized air dryers
Infrequent maintenance on your compressed air system
How to fix it:
Keep your powder storage area climate-controlled, ideally 60–75°F with <50% humidity.
Use a refrigerated air dryer and a desiccant filter on your compressed air line.
Check your air system daily. If you see water in the traps, fix it before spraying.
2. Dirty or Wet Compressed Air
Even a trace of oil or water in your air supply can cause powder to clump and spray inconsistently.
Joey Tip: If you wouldn’t drink the water from your air line, your powder shouldn’t either. Keep filtration clean, replace filters on schedule, and drain tanks regularly.
3. Poor Powder Fluidization
Fluidization is how powder in the hopper becomes a “boiling” cloud ready to be carried to the gun. If the fluidizing plate is clogged or the air flow is incorrect, powder will surge and spit.
Quick fixes:
Check the air pressure to the hopper, too low and the powder won’t lift; too high and it’ll blast out unevenly.
Clean or replace the fluidizing membrane if it’s dirty or damaged.
4. Old or Contaminated Powder
Powder has a shelf life. Once it’s expired, clumping is inevitable, especially if it’s been stored in humid or fluctuating temperatures. Contaminants like dust or debris will also cause inconsistent spray patterns.
Prevention:
Always rotate stock: first in, first out.
Seal opened boxes when not in use.
Never mix different powders in the hopper.
5. Gun Maintenance Neglect
If the powder path inside your gun is caked with residue, powder will clump and spit before it even reaches the tip.
Maintenance checklist:
Clean the gun daily, both internally and externally.
Inspect for wear on nozzles and venturis.
Follow the manufacturer’s cleaning instructions, no shortcuts.
6. Operator Technique
Rapid trigger pulls, spraying too close to the part, or inconsistent gun movement can all cause spitting, especially with metallic or specialty powders that need smooth, steady flow.
Pro Tip: Keep your passes consistent and let the gun feed before pulling the trigger on the part. Think of it like spraying paint, you want a smooth stroke, not a stutter.
The Bottom Line
Clumping and spitting are more than annoyances, they’re red flags in your process. Fix them, and you’ll not only save powder, but you’ll also deliver better finishes, reduce rework, and protect your profit margins.
