Overspray on 3D-printed parts
When we apply a sprayed finish (primer, paint, or a clear topcoat), the coating leaves the gun as a fine mist, not a neat brush line. Most of it lands where it’s aimed, but a little drifts. The drift that settles on surfaces you didn’t want coated is called overspray.
The illustration above shows the key idea: one part, the same “leave this unfinished” instruction on three different surfaces, with three different outcomes.
Why “unfinished” doesn’t always mean untouched
On our instant finishing quote, the faces you mark No-finish are pulled out of the surface-area price. That’s exactly what they’re for: they lower your cost. But “No-finish” tells us not to deliberately coat a surface. It can’t change where a fine mist physically travels.
Whether a given unfinished face stays perfectly clean or picks up a light haze comes down to one thing: is it in the line of the spray?
When unfinished surfaces can catch overspray
- Flat, open faces sitting right beside a finished area
- Surfaces angled toward the spray
- Shallow steps, fillets and edges close to the coated zone
These don’t get a full coat, just a fine, often barely-visible haze of the colour.
Overspray fades down an unfinished face sitting right beside the painted top.
When they stay clean
- Deep recesses, pockets, internal channels and bores
- Faces pointing away from the spray, the “back” of the part
- Anything we can physically mask off with tape or a plug
Paint on the outside, while the raw internal channel stays clean inside.
What we do about it
We mask, tape and plug the surfaces that have to stay raw, and we orient the part on the bench so the spray travels away from your No-finish areas. On straightforward shapes that’s a clean separation. On intricate geometry, a faint dusting on exposed faces can’t always be fully avoided, so we treat your No-finish marks as a pricing tool, not a promise of zero paint contact, and we review every part before we start. If something won’t come out the way you marked it, we’ll tell you before any work (or payment) goes ahead.
Not sure how your part will behave? Start a finishing quote and mark it up, or message us with a photo. We’ll tell you exactly what to expect.
Frequently asked
What is overspray?
Overspray is the fine mist of paint that drifts beyond the exact area being sprayed and settles on nearby surfaces. When we finish a 3D-printed part, surfaces right next to the painted area (especially flat, exposed faces) can pick up a light dusting, while recessed and back-facing surfaces usually stay clean.
Will the areas I mark as unfinished be completely paint-free?
Not always. Marking a surface as No-finish removes it from the finishing price, but it isn't a guarantee of zero paint contact. Exposed faces beside a sprayed area may catch light overspray; deep recesses, bores and back-facing surfaces almost always stay clean. We mask, tape and plug where practical and review every part before we start.
How do you reduce overspray on unfinished areas?
We physically mask, tape and plug the surfaces that must stay raw, orient the part so the spray travels away from those areas, and keep coats thin and controlled. On simple geometry that gives a clean separation; on intricate parts a faint dusting on exposed faces can't always be fully avoided.
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