Use a minimal, test-verified underbase when garment color or ink translucency would alter your intended colors, and aim for the minimum effective underbase rather than a heavy flood coat. The workflow runs from separation to mesh and ink choice, to a thin underbase print, a flash to gel, the overprint, and a final cure, with checks at each step. Expect mesh in the 110 to 230 range and flash targets near 190°F, confirmed on your own press the way Tekton LA and other production shops do before running a job.
TL;DR:
- Most shops overbuild the underbase, risking adhesion failure due to full curing and excessive stiffness; testing on your press ensures optimal settings.
- Fine underbase details require an appropriate mesh range between 110 and 230, with higher tension and controlled emulsion over mesh to balance opacity and hand feel.
- Proper flash temperature is near 190°F to gel the underbase without curing it fully, preventing topcoat adhesion issues during curing.
- Documented strike-offs for each garment, ink, and fabric are essential to identify the minimum effective underbase, saving time and reducing waste on future jobs.
- Testing on your equipment and materials is the only way to determine safe choke, pullback, and mesh settings, since industry defaults often lead to overbuilding.
Table of Contents
- What is an underbase and why it matters
- When does a job actually need an underbase?
- Preparing separations for a clean underbase
- Mesh, tension, and EOM: the real opacity levers
- Flash, gel, and cure settings that protect adhesion
- Strike-offs and the minimum effective underbase
- Shop standards worth copying
- Where most shops get underbase wrong
- Get your underbase settings right the first time
- Sources
- FAQ
What is an underbase and why it matters
An underbase is the layer of ink, usually white, printed first and cured or gelled before the top colors go down. Its job is to block the garment color from showing through and give the inks above it a neutral, opaque surface to sit on. A properly built underbase seals the fabric and reduces dye migration, though too much of it adds stiffness and can cause curing problems if it gets over-flashed.
Shops generally work with four underbase types:
- Solid white underbase: full opacity for bold graphics on dark cotton, the heaviest deposit and the stiffest hand.
- Halftone or tonal underbase: follows the dot pattern of the art above it, preserving detail in simulated process or photo-realistic designs.
- Colored underbase: a gray or tinted base that can cut the screen count and give a softer, vintage look.
- Clear underbase: used mainly to seal polyester against dye bleed without adding opacity.
Colored underbases save a screen when the top color is close to the base tone, but push the wrong hue and the final color shifts off target, so test before committing to production.
When does a job actually need an underbase?
Not every print needs one. Run through this before you burn a screen:
- Shirt color: dark or saturated garments usually need an underbase for bright, true colors; a faded or vintage look on a dark shirt can sometimes skip it on purpose.
- Fabric and dye: polyester and poly blends carry a real risk of dye migration into the ink, so a sealing underbase or low-bleed ink system matters more there than on cotton, a point covered in depth in shop-tested rules for polyester printing.
- Design complexity: halftones and simulated process work call for a tonal underbase that tracks the dot structure; flat color blocks are fine with a solid underbase.
- Special inks: metallics, fluorescents, discharge, and high-density inks each behave differently under or without a base, and discharge in particular changes how much underbase you even need.
Pro Tip: Print a same-garment test swatch with and without underbase before locking the job, since the difference is often more visible on fabric than on a monitor.
Preparing separations for a clean underbase
Separations make or break an underbase job. A white halo around the art almost always traces back to poor choke or pullback, not bad printing.
- Choke shrinks the underbase slightly inside the top art’s edges so no white rim peeks out; pullback does the reverse, slightly undersizing the underbase so the top ink fully covers it.
- Tight automatic presses with reliable registration can run as little as a 1-point choke, while manual presses with more registration drift often need 2 to 3 points to stay safe.
- Run a choke-test chart on your own equipment and measure the actual registration shift rather than guessing a value from another shop’s setup.
- For halftone art, build the underbase as a matching halftone, not a solid, so you preserve dot edges and avoid flattening fine detail into a mushy block.
- Reduce total screen count by using a tinted underbase where the top color allows it, or by letting an opaque top ink do double duty over a thinner base.
Hand the separations off with a checklist: confirmed choke or pullback value, underbase type (solid or halftone), intended mesh for each screen, and any special-ink notes, so the screen room isn’t guessing at intent.
Mesh, tension, and EOM: the real opacity levers
Mesh count and emulsion over mesh (EOM) decide how much ink lands on the shirt, and that decides both opacity and hand feel.
- Use 110 to 160 mesh for standard solid underbases where full coverage matters more than fine detail.
- Move to 180 to 230 mesh for fine-detail or halftone underbases, which holds small dots without flooding them shut.
- Historical shop practice spans 80 to 305 mesh for underlays, but the finer end of whatever range still meets your opacity target keeps ink deposit and hand weight down.
- Thicker EOM means a thicker, wetter ink deposit, which boosts opacity but adds stiffness and slows cure-through; dial coating passes to the minimum that still clears the mesh evenly.
- Higher screen tension keeps ink sitting on top of the fabric instead of forcing it into the weave, which softens the hand without losing opacity.
- A firmer squeegee durometer, in the 70 to 75 range for most shops, helps lay down a controlled, even underbase rather than flooding the stencil.
A useful starter combo for solid underbase on cotton is 156 mesh, moderate EOM, and a 70 durometer squeegee at firm but not maximum pressure; for halftone underbase work, step up to 200 mesh with a thinner EOM to protect dot edges.
The mesh range that governs most underbase decisions is 110 to 230, spanning everything from flood coverage to fine halftone detail, and most production problems trace back to picking a mesh outside that band for the art in question.
Flash, gel, and cure settings that protect adhesion
Flashing gels the underbase just enough to accept the next ink layer without fully curing it, and getting this step wrong causes more adhesion failures than any other variable.
- Target a gel temperature near 190°F (88°C) for plastisol underbases rather than full cure heat.
- Full plastisol cure happens in the 275 to 320°F (135 to 160°C) range, and that number belongs at the final dryer, not the flash station.
- Check actual garment surface temperature with a pyrometer or infrared thermometer rather than trusting the flash unit’s dial, since ambient conditions shift the real number.
- Turn flash units down and shorten dwell time to the minimum that gels the surface; over-flashing cures the underbase too far and breaks the mechanical bond the top ink needs.
Over-flashing the underbase is the single most common cause of topcoat separation after wash, according to flash-curing parameter guidance from the trade press, and it is almost always fixable by turning the unit down rather than changing ink.
Metallics and fluorescents often need a matte or slightly textured underbase to bond well, discharge ink changes the underbase math entirely since it works by removing dye rather than covering it, and polyester jobs benefit from a low-bleed ink system alongside the underbase, a combination covered further in guidance on water-based versus plastisol systems.
Strike-offs and the minimum effective underbase
A strike-off is a test print that isolates one variable at a time so you can find the lightest underbase that still does the job, rather than guessing and overprinting out of caution, a process well illustrated in the reflective and specialty ink printing techniques described by Modern Day Knight.
- Print a halftone dot grid from 0 to 100% along with a white-opacity ramp on your actual garment color and fabric.
- Run a choke test chart alongside it to confirm your separation values hold registration at production speed.
- Hold mesh, EOM, squeegee, and flash constant while you drop underbase deposit step by step until opacity just barely fails, then back up one step.
- Record the winning settings as your shop’s minimum effective underbase for that garment and ink combination.
Document mesh count, EOM, squeegee durometer, flash temperature and dwell time, and ink brand and type for every approved setting, then sample bulk production at a fixed interval, checking opacity, registration, hand feel, and a quick wash test for adhesion.
Pro Tip: Keep a troubleshooting card near the press: mottling usually means uneven EOM, orange peel points to too-cool flash, a white outline means choke was too tight, and topcoat separation almost always traces back to over-flashing.
Shop standards worth copying
A shop that writes down its underbase settings stops re-solving the same problem every job. A workable template standard looks like 156 mesh for solid underbase, moderate EOM, a flash target near 190°F, and a 70 durometer squeegee, adjusted only after a documented strike-off shows the change is needed.
- Treat every new garment color or fabric blend as its own strike-off, not a guess based on the last similar job.
- Store the winning settings where the press operator can see them, not just in a separations file.
- Preserving a strike-off print alongside the settings gives you a physical reference when a customer disputes color or hand feel months later.
Production shops like Tekton LA, running jobs in Downtown Los Angeles with fast turnaround and no minimum order quantities, build exactly this kind of recorded baseline because repeat orders need to match the first run, not just look close. That discipline, more than any single mesh number, is what separates a shop that can rerun a job in a year from one that has to start over.
Where most shops get underbase wrong
The industry default is to overbuild the underbase, flood coat, heavy mesh, full cure before the top color goes down, because it feels safer than testing. That instinct is backward: a heavier underbase doesn’t just stiffen the hand, it raises the odds of exactly the adhesion failure it was meant to prevent, since a fully cured base gives the top ink nothing to grip.
The bigger gap is documentation, not technique. Most shops can print a decent underbase once; few write down the mesh, EOM, flash temperature, and squeegee setting that got them there, so the next run of the same job becomes a new experiment instead of a repeat. A strike-off chart costs one screen and ten minutes. Skipping it costs a reprint or a client who notices the second batch doesn’t match the first.
If you take one thing from this, prioritize the test chart over the recipe. Mesh 110 to 230 and a 190°F flash target are a starting point, not a universal answer, and the only way to know your actual minimum effective underbase is to print the grid on your own press, your own ink, and your own garment.
— Christian
Get your underbase settings right the first time
Testing mesh, EOM, and flash settings takes equipment and time that not every brand or event has sitting around, and a bad first run on a bulk order is expensive to fix after the fact. Tekton LA runs screen printing alongside DTG, DTF, embroidery, and garment dye out of Downtown Los Angeles, with no minimum order quantities and fast turnaround for jobs that cannot wait on a slow production queue.
If you have dark garments, polyester blends, or detailed halftone art that needs a properly built underbase, our 2 color screen print service covers the separations, mesh selection, and flash-to-cure settings so the first batch matches the tenth. Check availability for your next run at Tektonla.
Sources
FAQ
What is underbase in screen printing?
An underbase is the opaque layer, almost always white, printed and gelled before the top colors to block the garment’s own color from showing through. It gives the inks above a neutral surface, which keeps colors true on dark or colored fabric.
What are the three main types of screen printing?
Screen printing itself is one mechanical ink-transfer process using a stencil method, typically photo emulsion for precision work. Within underbase technique specifically, printers commonly choose between solid, halftone or tonal, and colored or clear underbases depending on the art and fabric.
Is screen printing illegal?
No, screen printing is a standard commercial printing method used across apparel, promotional goods, and fine art, and it carries no general legal restriction. Specific designs can raise copyright or trademark issues depending on the artwork used, which is a separate question from the printing process itself.
What does substrate mean in printing?
Substrate refers to the material being printed on, such as a cotton t-shirt, a polyester jersey, or a tote bag. The substrate’s fiber content and color directly affect underbase decisions, since polyester tends to carry more dye migration risk than cotton.
How do I find the minimum effective underbase for a job?
Run a strike-off with a halftone dot grid and a white-opacity ramp on your actual garment, holding mesh, EOM, squeegee, and flash settings constant while you reduce underbase deposit step by step. Stop at the lightest deposit that still meets opacity, then record those settings as your shop standard for that garment and ink combination.