When to Screen Print a Gray Blocker Base (and How to Do It Right)
In the world of screen printing, nothing ruins a crisp design faster than dye migration. That’s where a gray blocker base comes in—a specialized underbase layer that stops dyes in their tracks. If you’re printing on troublesome fabrics like polyester, tri-blends, or sublimated garments, it may be your best defense.
What Is a Gray Blocker Base?
A gray blocker base is typically a high-opacity, low-bleed gray plastisol ink formulated with dye-blocking agents. It’s used as an underbase layer beneath your white or color inks, especially when printing on garments prone to dye migration, like:
- 100% polyester shirts
- Sublimated polyester hoodies or jerseys
- Camo patterns
- Neon-colored or deeply dyed garments
- Athletic wear and team uniforms
The idea is simple: lay down a gray layer to trap the dyes before they rise into your white ink or top colors during flash and cure.
When Should You Use a Gray Blocker Base?
Not every job needs it. But here’s when it’s essential:
1. Printing White Ink on Polyester
White ink is most affected by dye migration. If you’re printing white on red, maroon, kelly green, or royal blue polyester, dye migration will likely cause a color shift within 24–48 hours of curing.
2. Sublimated Garments
Sublimated patterns look great—until you print on them. Sublimation dyes are notorious for gassing out during flash or cure. A blocker base creates a physical barrier to stop this.
3. Camo and Deep-Dyed Fabrics
Military-style prints, charcoal heather, or deep neon tones are often discharge-resistant and bleed-prone. Blocker base gives your design a neutral foundation.
4. Athletic Jerseys
Uniforms with numbers or sponsors printed in white on colored polyester need stability. Gray blocker ensures the color stays white and doesn’t turn pink or blue from migration.
How to Print a Gray Blocker Base Properly
1. Use the Right Ink
Use a plastisol blocker base made specifically for dye migration—look for terms like “Barrier Gray” or “Blocker Base”. Avoid standard gray inks.
2. Artwork Setup
Add a separate blocker base plate under your underbase white in the art file. The blocker doesn’t need to hit edges perfectly—just cover all printed areas.
- Print order: Gray Blocker ➝ Flash ➝ White Underbase ➝ Colors
- You can choke the blocker layer slightly (0.5 pt) to prevent registration issues.
3. Mesh Count
- Use 86–110 mesh for your blocker. It’s thick, so you don’t want too fine a mesh.
- Coat screens for a heavy stencil (typically a 2/2 coating with the round side of the scoop coater to increase EOM).
4. Flashing
- Flash the blocker just enough to gel—do not over-flash or you risk creating intercoat adhesion issues.
- Temperature should hit ~220°F on surface temp; dwell time ~3–5 seconds.
5. Print Your Underbase and Top Colors
After the blocker is flashed:
- Print your white underbase on top using a slightly higher mesh (110–160).
- Flash again lightly if needed, then print your top colors.
Optional: Stackable Bases
On extreme bleed fabrics, consider printing the gray blocker, flashing, then stacking a white blocker (like a bleed-resistant white), flashing again, and then doing the color top coat.
Final Thoughts
Gray blocker bases aren’t needed for every job—but when they are, they’re the only thing standing between your bright whites and a ruined print. Understanding when to use them and how to implement them correctly ensures long-lasting prints and happy customers.
Pro Tip: Always test the garment before running a full job. Print, flash, and cure—then heat press at 300°F for 10 seconds and observe any color shift. If migration happens, a blocker base is non-negotiable.
When to Screen Print a Gray Blocker Base (and How to Do It Right).pdf
