Backing Material & Fastening It to HDU

[John Hollaway]

Greetings. While I've been making sawdust in my shop for nearly 40 years, I'm a complete rookie at sign making. Perhaps some of you will lend me a hand.

Presently I'm router carving several replica Pennsylvania Railroad station signs, the largest being about 8 feet long, from 1", 15 lb. density HDU. Although these signs will be wall mounted, I'd still like to mount some backing material to the sign board for stiffening - but not plywood. The HDU manufacturer recommended .080 aluminum sheet for the backing, or even strips of heavier aluminum, but I'd like to hear your opinion. Also, how would you recommend such backing be attached to the HDU? Thanks.

John

[bleeth]

I would use di-bond, buy it with a color finish, scuff it up, and use an epoxy made for aluminum. Available at Grainger's, CR Laurence, etc. I've used one from Lock-weld. You can also bond with 5200.

[joe]

John,

This is a regular topic of discussion among Sign people. All over this country people are asking the same question. Here's my take on it.

What you're dealing with is materials with difference in expansion rates. Aluminum seems to have a closer expansion to HDU than most other materials but it is different. My experience with DiBond is awful. It will warp like crazy. I'd suggest you run a little test and place it outdoors for a few days. Dave Rosenbleeth much not have done his tests. I have some photo's to show if needed. Also, MDO isn't a good option either. You really don't need to do anything to the back of your sign if it's going up against the wall. Prime and paint is your best option. Watch out when using screws. HDU hates them also.

Joe Crumley

[kerrazy]

Ensure however many coats of finish,primer or otherwise you put on front, match it on the back. Other wise as my good friend Joe mentioned you will get warping.
You need to balance the surface tension on both sides to avoid cupping or warping.
I would mill in 1/2" deep Pockets to accept 3" x 1/2" MDO CLEATS. And then I would epoxy resin the MDO in place and again top coat to match face of sign. I have a few signs 10+ years still going strong with this form of support .