How to Build Reverse Channel Letters Without Welding
The short version. You don’t have to weld reverse channel letters. Tack the return to the face with Surebonder 925 acrylic hot melt, then run LORD Signlok 406 structural acrylic along the inside seam. The hot melt holds the letter in position. The Signlok 406 bonds and seals it. No sparks, no grinding, no heat distortion.
Welding is where most reverse channel letter jobs lose money. A .063 return takes heat distortion, every seam needs grinding and filling, oxide cleanup eats hours, and a halo letter shows every flaw the second the LEDs come on.
Bonding takes that off the table and drops the skill level needed on the bench. Here’s the process, the products, and the numbers behind it.
Tack Hold
PSI Lap Shear
Handling Strength
Weld Seams
Watch the Build
Shaping, tacking, and seaming a reverse channel letter start to finish.
Why Bond Instead of Weld
- Heat distortion on .050 and .063 returns
- Grinding, sanding, and filling every seam
- Oxide cleanup before and after
- Certified or highly skilled labor
- Welds can shear as aluminum fatigues
- Sparks, rust risk, read-through on halo letters
- No heat input, so letter geometry stays crisp
- No weld seams to grind or fill
- Bonds untreated aluminum, minimal prep
- Bench-level labor, faster to train
- Seals light leaks in the seam before paint
- Same process for aluminum, stainless, ACM, polycarbonate
Spot welding returns onto faces creates a strong bond, but aluminum can shear at the welds under stress over time. A thin coat of adhesive on the seam adds durability, and fills the small light leaks before paint.
Signs of the Times, Adhesives in Sign Manufacturing
What a Reverse Channel Letter Is Made Of
Reverse channel letters are aluminum. The return wraps the perimeter and joins to the face, and a clear polycarbonate back closes the letter so the LED output reaches the wall. Standard construction across the trade runs about like this.
The Signlok 406 bond happens at the face-to-return seam. The polycarbonate back mounts separately so the LEDs stay serviceable. Worth noting that UL 48 governs the finished sign assembly, while the UL 746C recognition on Signlok 406 applies to the adhesive material itself.
How to Build One With Adhesive
STEP 01
Shape
Cut and bend the return and face into the letter profile. Nothing changes from your normal process here.
STEP 02
Tack
Run Surebonder 925 hot melt sticks through the CCH220 gun to tack the return to the face as you form the letter. Tacks hold in about 60 seconds. The hot melt is your clamp, not your bond. Set the thermostat between 350 °F and 390 °F for consistent flow.
STEP 03
Seam and Bond
With the letter tacked and holding shape, run LORD Signlok 406 along the inside of the face-to-return seam in place of welding. It seals as it bonds, which closes light leaks before the letter goes to paint.
Letters move from bench to paint in under 20 minutes.
Let the Signlok 406 cure before the letter hits the oven. The 925 hot melt has a 165 °F softening point, so it’s a fixturing aid, not the load path. Once the 406 is cured it carries the joint, and it handles bake cycles up to 149 °C (300 °F).
The System
Three products cover the whole build.
The Structural Bond
LORD Signlok 406
Two-part acrylic. 6 to 10 min work time, UL 746C recognized, bonds untreated metals and plastics. This is what replaces the weld.
The Tack
Surebonder 925
100 percent solids acrylic hot melt, 1/2 in. x 10 in. sticks. Holds the letter in shape while the structural adhesive cures. Not structural on its own.
The Applicator
CCH220 Hot Melt Gun
220 watt industrial gun for 1/2 in. sticks. Comes with stand, on/off switch, and adjustable thermostat.
For dispensing the Signlok cartridges you’ll also want the 520 Dual-Component Gun, an 18:1 thrust ratio cartridge gun built for the Signlok series with snap in / snap out push disks, a cartridge stabilizing plate, and a heat treated piston rod. Static mixers sold separately.
Technical Data
The 925 is a fixturing aid. Tacks hold in about 60 seconds in shop conditions, which is a working observation rather than a published spec. Structural strength comes from the Signlok 406.
Compatible Substrates
Brushed or painted aluminum, stainless steel, ACM, galvanized sheet, polycarbonate, ABS, acrylic, and powder coated parts.
Mounting the Finished Letters
Adhesive works for the install too.
- Bond surface mount fasteners to the backs of the letters. Replaces drilling and stud welding.
- Attach threaded rods to the studs. A threadlocker can be added where extra strength is needed.
- Drill the wall and fill the holes with an epoxy or anchoring adhesive.
- Set the sign and push the threaded rods into the adhesive in the drilled holes.
- Temporarily secure the sign with tape while the adhesive cures.
Letters can sit flush to the wall or stand off it 1.5 to 2 in. on standoffs, which is what sets how wide the halo spreads.
100 percent silicone gets recommended for the wall holes sometimes. Use a true structural adhesive instead. Silicone doesn’t carry that load the same way.
Lighter Loads and Interior Installs
For interior work with a lighter load, double sided high bond acrylic foam tape handles the mount with no visible fasteners. Chem-Set VST 6120G is a 47 mil gray acrylic foam tape with high initial tack, and the conformable core absorbs the difference in thermal expansion between two dissimilar substrates.
Design the joint for shear and tensile loading. Cleavage and peel forces are what pull foam tape off a letter. Surfaces need to be clean and free of fingerprints and light oil, and low surface energy substrates need a primer. Apply above 65 °F, roll it down with pressure, and expect full strength after 24 hours at ambient.
Packaging and Ordering
Common Questions
Can you build channel letters without welding?
Yes. Acrylic hot melt tacks the return to the face, then a two-part structural acrylic like LORD Signlok 406 bonds and seals the seam. The bonded joint holds without heat, sparks, or grinding.
What adhesive replaces welding on channel letters?
LORD Signlok 406. Two-part acrylic, 6 to 10 minute work time, 2,000 psi lap shear on aluminum, UL 746C recognized, bonds untreated metals and plastics.
What gauge aluminum are reverse channel letters made from?
Faces are typically .090 aluminum, with .080 to .125 on larger letters. Returns are usually .063, sometimes .050 on lighter work. Backs are 3/16 in. clear polycarbonate or Lexan. Signlok 406 bonds the face-to-return seam across that whole range.
Is the hot melt holding the letter together?
No. The Surebonder 925 tacks the return to the face so the letter holds its shape and the fabricator can keep working. LORD Signlok 406 is what bonds and seals the seam and carries the load.
Will a bonded seam leak light on a halo letter?
The opposite. Signlok 406 seals the seam as it bonds, so it closes the small gaps that show as light leaks once the LEDs are on. That happens before paint, so there’s no chasing leaks after finishing.
How long before a bonded letter can be handled?
Signlok 406 reaches handling strength in 12 to 17 minutes at 24 °C. The hot melt tacks set in about a minute, so the letter keeps its shape while the structural adhesive works.
Do you need to prep the metal first?
Signlok 406 bonds untreated metals and plastics, so prep requirements are minimal next to welding, which needs oxide cleanup and post-weld grinding.
Will bonded letters survive a powder coat bake?
Signlok 406 is compatible with powder coat bake cycles up to 149 °C (300 °F). Cure the 406 before the letter goes in, since the 925 hot melt softens at 165 °F and is only there to fixture the parts.
Can foam tape replace the adhesive on the mount?
For interior installs with lighter loads, yes. Chem-Set VST 6120G carries 86 lb/in² in dynamic shear and 23 lb/in. in 90° peel. Design for shear and tensile rather than peel, and check the substrate. Low surface energy materials need a primer.
Want to Run a Test Letter?
We’ll help you spec the cartridge count, mixers, and gun setup for your volume. Sample material available for a first run.
