Using structural frames for high-density urethane signs

By signcraft

Posted on Friday, May 20th, 2022

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One popular method of strengthening high-density urethane (HDU) sign panels is to laminate the sign face to another substrate to get the structural integrity needed for the installation. Some shops use overlaid plywood, aluminum composite board or PVC board for this task. But what do you use when that’s just not strong enough?

Most SignCraft readers are familiar with the boundary-stretching design work of Dan Sawatzky, Sawatzky’s Imagination Corporation of Chilliwack, British Columbia. With the addition of a MultiCam router, Dan discovered a world of new possibilities. The router offered them unlimited precision and creativity in one neat package.

With Sawatzky’s Imagination Corporation’s previous experience in theme park design and construction, it is their firm intention to push the boundaries of conventional design for all of the signs coming out of their shop.

They have been making most of their routed signs from 30-lb. Precision Board HDU. It allows them to route in fine detail and makes for a tough finished sign. It also minimizes the time required for finishing. But Dan quickly learned that even this denser HDU that he prefers needs additional structural strength in many applications.

Adding strength and mounting points

Laminating the sign face to another substrate was a good idea, but Dan felt it wouldn’t do for most of their installations. The Sawatzky team has plenty of experience with welded structural steel for their fiberglass reinforced concrete projects, and Dan decided to incorporate similar frames within the HDU signs they were fabricating.

The steel frames allow them to build signs in virtually any thickness without using excessive amounts of expensive HDU. These frames also free them from design constraints as the frames provide the structural integrity. The HDU is merely the three-dimensional skin that surrounds it. It also allows them to hide the framework and mounting points within the sign itself.

“Fabricating the structural attachment points as an integral part of these frames,” says Dan, “makes the mounting of the routed sign components a relatively simple procedure. The signs can hang from virtually any point. In the process, function becomes secondary to the design—a wonderful place to be as a designer. It lets you design first and then figure out just how to build the physical sign later. There are few limitations. With structural steel mounting points, the supporting structure can either be a major feature of the sign or almost invisible—yet still be very, very strong.”

Lift points for transport and placement are also simple to incorporate with an internal welded steel frame. Dan uses eyebolts rated for 20,000 lbs. or more, which simply unthread when the project is installed. By inserting a pre-finished HDU plug into these holes the lift points disappear in seconds.”

Dan and his crew often build a temporary steel frame to mount their signs on during fabrication. By adding some heavy-duty dolly wheels to these temporary structures they can move them around the shop, making the most of their workspace.

Dan Sawatzky’s shop, Sawatzky’s Imagination Corporation, is in Chilliwack, British Columbia, Canada.

This article appeared in the May/June 2007 issue of SignCraft.

The pieces were routed on their MultiCam CNC router from 30-lb. Precision Board HDU. Dan laid the precut pieces on the floor and lined them up carefully. Then he spread Coastal Enterprises’ PB Bond 240 adhesive on the HDU and placed the frame, which was welded from 1-by-1-by-1 ⁄8-in. wall steel tubing.

The edges and gaps around the steel frame were filled with precut pieces of scrap HDU board. Dan glued on the opposite faces and clamped it all up until dry.

After the clamps were removed he used the eyebolt that was fastened to the frame to lift and hold the piece in position while welding up a frame for the base. The pencil rod framework, lath and cultured stone on the base still need to be added.

Now it was time to glue up the round logo, which stood off the face of the sign. Multiple layers of HDU make up a hollow shell to minimize material cost.

When dry, the logo was bonded to the sign assembly. Each logo assembly was bonded on one at a time to make it easier to keep things lined up. Plenty of clamps were used to keep it in line until the adhesive set up.

This shot shows the back before installation of the logo. The square tubing frame isn’t fancy, but it’s plenty strong and gives strength to the HDU skin.

The hollow areas at the bottom of the sign that wouldn’t be covered with rockwork were filled in with scraps of HDU that were saved for just such a purpose.

An air-powered die grinder with a round-tipped bit made short work of adding wood grain to the ends and sides of the sign. Dan also used the same tool to add texture to the edges of the round logo disk.

Once the HDU was assembled and shaped, it was time to weld up a pencil rod framework for the cement and stonework. The pencil rod was welded to form a 6-in. grid to which Dan attached the expanded mesh.

A scratch coat of concrete was troweled on and allowed to set, then Dan fit and set the faux rockwork in place, covering the entire base.

The router-cut beveled letters were also made of 30-lb. Precision Board HDU. These were gilded using 1Shot [219-949-1684,] quick size and then attached using silicone adhesive. [UPDATE: Dan says that today they never rout the letters separately, but rather use a thicker board to start with that can accommodate their woodgrains, textures and raised dimensional letters. They rout the sign faces in one piece. They still laminate steel structures inside as before.  They always use PB Bond glue or PB Fastset to bond Precision Board. –Editor]

With the eyebolt fastened into the sign, it was a simple matter of hooking it up to the shop’s gantry crane and lifting the sign two feet off the ground to back the flatbed trailer underneath. The sign balanced perfectly—a lucky guess on eyebolt placement by Dan. The sign was loaded and ready for transport to its permanent home.


Dan uses a steel frame inside even small HDU signs like this one.