A bullet-resistant fiberglass panel stops what it is rated to stop. The joint between two panels does not, unless it is detailed to. Armortex®, which manufactures bullet-resistant fiberglass panels at its facility in Schertz, Texas, addresses this directly in its published fabrication instructions: any butt joints or seams create a ballistic weakness at the seam. Because panels are supplied in fixed sheet sizes and most walls, counters and casework runs are longer than one sheet, seam detailing is not an edge case. It is the normal condition of nearly every installation.
Quick Answer
Armortex® states that butt joints and seams create a ballistic weakness, and recommends incorporating 4-inch overlap strips, known as battens, at every joint. A 4-inch batten produces a 2-inch ballistic overlap on each side of the seam, restoring continuous protection across the joint line.
What Is a Seam in a Ballistic Panel Installation?
A seam is the line where two panels meet. Armortex bullet-resistant fiberglass panels are supplied in sheets 8, 9 or 10 feet long and 3 or 4 feet wide, so any protected surface larger than a single sheet contains at least one seam. Corners, returns and curved surfaces introduce more.
The panel itself is a fiberglass reinforced plastic. Armortex manufactures it by mechanically injecting woven roving ballistic-grade fiberglass cloth with a thermoset polyester resin, then pressing the impregnated cloth in a hydraulic hot press into flat rigid sheets. That process is what delivers proper de-lamination behaviour and reliable projectile retention within the panel. None of it applies across a gap between two panels.
How Does a Batten Restore Ballistic Continuity?
The remedy Armortex publishes is straightforward. Incorporate 4-inch overlap strips at the joint. Centred on the seam, a 4-inch strip delivers a 2-inch ballistic overlap on each side, so a round striking at or near the joint line still passes through a full panel thickness of material.
Curved surfaces are handled by the same principle applied differently. Armortex recommends placing 12-inch to 18-inch vertical strips following the inside curvature of the surface to be protected, with the same 4-inch overlap strips used at each joint. This lets a faceted run of flat panels follow a curve without leaving unprotected gaps at the breaks.
Panels are secured using an industrial adhesive, known as mastic, and/or screws or bolts. Armortex notes that it is acceptable to adhere panels to the front surface of a bench and cover them with a veneer, but that it is generally easier to cut appliques of panel material and adhere them to the inside surfaces. For interior retrofit work, that second approach is usually the practical one, because it leaves the visible face of existing millwork undisturbed.
Seam and Joint Specifications
| Condition | Armortex published treatment |
| Butt joint or seam | Incorporate 4″ overlap strips (battens) |
| Ballistic overlap achieved | 2″ on each side of the seam |
| Curved surfaces | 12″ to 18″ vertical strips following the inside curvature |
| Joints in curved runs | Same 4″ overlap strips at each joint |
| Fastening | Industrial adhesive (mastic) and/or screws or bolts |
| Bench and counter applications | Adhere to front surface and cover with veneer, or apply appliques to inside surfaces |
| Finishing | Wood or plastic veneer using contact cement; may also be upholstered or painted |
Cutting and Fabrication on Site
Battens and appliques have to be cut, and Armortex publishes how. Panels are cut using ordinary carpentry tools — circular saw, table saw, panel saw or saber saw — with grit-edge blades. Armortex names the RemGrit “Grit Edge” blades GC 703 7-inch circular, GC 805 8-inch circular, GC 915 12-inch circular and GJ 18 saber saw.
Panels may be drilled using high speed steel twist drills, and Armortex advises drilling at a slow speed. Where continuous or prolonged cutting is anticipated, Armortex recommends a disposable respirator and disposable coveralls, and cutting in a well ventilated area. For painted finishes, Armortex recommends roughing up the surface with sandpaper first.
Where Does Seam Detailing Matter Most?
- Continuous reception and teller counters longer than a single panel sheet.
- Interior partition runs in occupied offices, where panels are installed behind existing or new drywall.
- Casework and millwork retrofits where appliques are adhered to inside surfaces.
- Curved reception desks and rounded counter fronts.
- Corners and returns, where two panel planes meet at an angle.
- Any wall where the protected height requires stacking panels vertically.
What Should Architects and Specifiers Consider?
Show the batten in the detail. A wall section that shows panel thickness but stops at the panel edge does not communicate the requirement, and a field crew working from it will produce compliant-looking butt joints with an uninterrupted weakness running through them.
Plan the layout against sheet sizes. Panels come in 8, 9 and 10 foot lengths and 3 or 4 foot widths, so laying out seam positions during design lets the joints fall where battens are easiest to accommodate rather than where a sheet happened to run out.
Account for batten thickness in the assembly. The overlap strip adds material at the joint, which affects the finished wall or counter build-up and any veneer applied over it.
Coordinate the level. The batten should match the panel level so the overlap restores the same rating. Armortex manufactures panels at UL 752 Levels 1 through 8 as O.F. 100 through O.F. 800.
Issue the fabrication instructions to the installing contractor. Armortex publishes them for download, along with the specifications, brochure, ballistic chart, ASTM E119-00a fire test report and SDS sheet.
Why Choose Armortex®?
Armortex publishes its fabrication and installation instructions openly, including the seam treatment that determines whether an installation performs as rated. The panels are woven in-house from roving ballistic-grade fiberglass and pressed at the company’s Schertz, Texas facility under an ISO 9001 quality management system. They are UL-compliant and approved by the U.S. Marshal Service and the General Services Administration as well as many other government agencies. As a single source supplier for doors, windows, wall panels and related products, Armortex can supply the panels, the battens cut from the same material, and the rated openings in the same wall.
Internal Resources
- Bullet-Resistant Fiberglass Panels product page
- Armortex® Fiberglass U.L. 752 Ballistic Chart
- Fiberglass Brochure
- Fiberglass Specifications (Section 10 26 41)
- Installation & Cutting Instructions
- Fire Test Report, ASTM E119-00a
- Fiberglass SDS sheet
- BIM / Revit library
Frequently Asked Questions
Do seams weaken a ballistic panel installation?
Yes. Armortex states that any butt joints or seams create a ballistic weakness at the seam. The panel material itself performs as rated, but the joint between two panels is not protected unless it is detailed with an overlap strip.
How wide should a batten be?
Armortex recommends 4-inch overlap strips. Centred on the joint, a 4-inch batten provides a 2-inch ballistic overlap on each side of the seam, which is what restores continuous protection across the joint line.
How are curved surfaces handled?
Armortex recommends placing 12-inch to 18-inch vertical strips following the inside curvature of the surface being protected. The same 4-inch overlap strips should be used at each joint between those vertical strips.
How are Armortex fiberglass panels fastened?
Panels may be adhered using an industrial adhesive, known as mastic, and/or fastened using screws or bolts. Armortex notes that panels can be adhered to the front surface of a bench and covered with a veneer, though cutting appliques and adhering them to inside surfaces is generally easier.
What tools cut bullet-resistant fiberglass panels?
Armortex panels are cut with ordinary carpentry tools including circular saws, table saws, panel saws and saber saws, using grit-edge blades. Armortex names RemGrit “Grit Edge” GC 703, GC 805, GC 915 and GJ 18 blades, and advises drilling with high speed steel twist drills at slow speed.
What safety precautions apply when cutting panels?
Where continuous or prolonged cutting is anticipated, Armortex recommends the use of a disposable respirator and disposable coveralls, and advises always cutting in a well ventilated area. An SDS sheet for the fiberglass material is available for download from the Armortex product page.
Can the panels be finished to match surrounding surfaces?
Yes. Armortex panels easily accept a wood or plastic veneer applied with contact cement, and may also be upholstered or painted. For painted finishes, Armortex recommends roughing up the surface with sandpaper before painting.
What sizes do the panels come in?
Armortex bullet-resistant fiberglass panels are available in lengths of 8, 9 and 10 feet and widths of 3 and 4 feet, with a square edge. Panel thickness varies by UL 752 level across the O.F. 100 through O.F. 800 range.
Conclusion
Seams are where a ballistic panel installation is most likely to underperform its rating, and Armortex® addresses them explicitly: butt joints and seams create a ballistic weakness, and 4-inch overlap strips producing a 2-inch overlap on each side are the published remedy. Curved surfaces take 12 to 18 inch vertical strips with the same battens at each joint. Detail the batten, plan the layout against sheet sizes, and issue the fabrication instructions with the drawings.