Is Laser Marking Readable After Painting or Galvanizing? How Deep to Mark

By Rex HangDirector Consultant Expert, HeatSign · 10+ years in industrial marking · LinkedIn · Updated September 2026

Is laser marking readable after painting or galvanizing? Often it is not. A steel shop marks a part number on every plate. The plates go out to be galvanized. They come back, and half the numbers are gone. Now the site crew has to match parts to drawings by hand.

A mark that looks sharp on the bench can disappear under paint, zinc or blasting. The fix is simple: the mark must be deeper than what the finish adds or removes.

For hot-dip galvanizing, the American Galvanizers Association (AGA) asks for marks at least 0.8 mm deep and 13 mm tall. This guide shows the depth you need for each finish, which machine can do it, and when it is easier to mark after coating.

Why Do Part Marks Disappear After Galvanizing, Blasting or Painting?

A finish can hide a mark in three ways. A coating fills it in: hot-dip zinc adds about 45–85 µm. Blasting grinds off the top layer. Acid and heat wipe out light laser marks. So the mark must be deeper than the finish.

Think of it like snow on a road sign. A thin layer is fine. A thick layer covers the letters. Some finishes add a layer on top of your mark. Some remove the surface the mark sits in. Some attack the mark with acid or heat.

Hot-dip galvanizing does all three. First the steel is cleaned in acid. Then it goes into melted zinc at about 450 °C (840 °F). So ask one question: is my mark deeper than what this process adds and takes away?

How Deep Does a Mark Need to Be for Each Finish?

For hot-dip galvanizing, mark at least 0.8 mm (1/32 in) deep and 13 mm (1/2 in) tall, as the American Galvanizers Association advises. Thin e-coat paint is easy. Blasting, powder coat and thick paint are in between.

Find your finish in the table. It tells you how deep to mark and which tool works.

An Easy Rule for Galvanized Parts: About 10 Times the Zinc

The AGA asks for 0.8 mm. On steel thicker than 6 mm, the zinc layer is usually at least 85 µm (ISO 1461). 0.8 mm is about 10 times that.

Does the Steel Thickness Change the Depth?

Yes. Thick steel picks up more zinc than thin steel. Heavy beams and castings need the full 0.8 mm. Thin brackets (under 1.5 mm) get about 45 µm of zinc, so about 0.5 mm is a safe start. Still test it.

Is Laser Marking Readable After Painting or Galvanizing?

Usually not. A fast laser mark is only a thin dark layer on the surface. Colored paint covers it, and the galvanizer’s acid bath removes it. A deep laser engraving can survive, but reaching 0.8 mm takes dozens of passes on every part.

When a fiber laser marks steel quickly, it only darkens the surface. There is almost no depth. Under primer or colored paint, that dark layer is simply hidden. Before galvanizing, the steel is cleaned in acid to remove rust and dark layers, so the laser mark goes with them.

A dent is different. Thin paint can cover the color, but it does not fill a deep dent. You can still see the letters by their shadow.

A laser can also engrave, which means it burns away metal. But one pass (one run of the laser) removes only about 0.01–0.02 mm in our experience. To reach 0.8 mm, you would need dozens of passes. That is too slow for most production.

So is laser marking readable after painting? Only when the mark is a deep engraving. If parts are painted or galvanized after marking, a fast laser mark is the wrong tool. A laser is a good choice after the finish. It marks the finished zinc or paint cleanly and fast.

Dot Peen or Laser: Which One Holds Up Better?

Dot peen is the safer choice before galvanizing and thick paint, because it presses deeper. A laser is better for thin e-coat, small Data Matrix codes and fine logos. Both can survive blasting, but a laser needs about 12 passes for each Data Matrix code.

Here is how the two compare for each finish.

The laser numbers come from one laser supplier’s published tests on die-cast parts. Our standard pneumatic dot peen machines reach about 1 mm deep. Custom builds can reach about 2 mm in softer metals. A small electric dot peen marker (about 0.05–0.3 mm per pass) is not deep enough for galvanizing.

Which Machine Should You Look At?

Pick by the size of your parts and what happens to them next.

Handheld Pneumatic Dot Peen MarkerA strong handheld pneumatic marker for beams, frames and thick steel. It punches deeper than a standard dot peen, so numbers last through zinc, blasting and paint.View machine →Desktop Pneumatic Dot PeenFor small and medium parts on a bench or a line. About 1 mm deep. Good before blasting, powder coat or zinc.View machine →Desktop Fiber LaserFor marking after coating, e-coated parts, small Data Matrix codes and logos. Fast and clean.View machine →

Should You Mark Before or After Painting or Galvanizing?

Mark after coating when you can, because then nothing can cover the mark. Mark before coating only when you must track each part through the finishing line. Then mark at least 0.8 mm deep, or hang a steel tag on it.

Three mistakes come up again and again:

Writing numbers in paint

Oil paint and crayon do not wash off in the acid bath. The zinc will not stick there, and the galvanizer may charge you to fix it. Use a water-based marker for temporary numbers.

Marking too close to a bend

A Data Matrix code 5 mm from a bend can stretch so much that it no longer scans. Keep it at least 15 mm away.

Forgetting the paint after marking

Marking a painted part can crack the paint around the mark. On outdoor steel, plan a quick touch-up.

How Do You Keep a Data Matrix Code Readable Under a Coating?

Make the code squares bigger and test a coated sample. Published tests used 0.6 mm squares to survive shot blasting and 1.25 mm squares under e-coat. Under thick paint (320 µm or more), mark the code after painting.

A Data Matrix code is a small square barcode, a bit like a QR code. Factories mark it on parts so a scanner can read the serial number.

A person can still read letters under paint from their shadow. A scanner cannot do that. It needs clear contrast between the tiny squares. Paint fills the squares first, so codes fail before text does.

If a customer audits your Data Matrix codes, “it scans in the shop” is not enough. Check the code after the finish, and grade it with the standard made for marks on metal: ISO/IEC 29158.

How Should You Test a Mark Before Production?

Mark five to ten real parts. Send them through your real galvanizer or paint line. Then read the text, scan the Data Matrix codes and check their grade (a quality score from a code checker). A test batch costs a few days. A failed production run costs far more.

Choose the shallowest depth that passes, not the deepest. Deeper marks take longer and wear the pin faster.

Frequently Asked Questions

What Should You Decide First?

The most common mistake is choosing the machine first and the finishing process second. People buy a laser because the marks look great at a trade show, then send the parts to a galvanizer. Or they buy a small electric marker for a shop that blasts every part.

Do it the other way around. Asking “is laser marking readable after painting?” is a good start, but the answer depends on the paint and the depth. List every step the part goes through after marking. Take the toughest step and find it in the depth table. That row tells you how deep to mark, which tool works, and whether to mark before or after.

Want a second opinion? Tell us about your parts and your finishing line. We will tell you honestly which machine fits, even if it is not the most expensive one.