I started in signs in 1974 and acrylic cutout letters were a common sign industry product. Acrylic was the standard material for cutout graphics (though MDO was often used).
The industry's "best practice" called for cast (not calendered) acrylic. The most common thickness was 3/16-inch, though quarter-inch was not uncommon on larger letters. 1/2-inch and 3/4-inch thicknesses were rarely used—these thicknesses were a needless expense, both in material and fabrication, unless an architect required it.
Mounting was accomplished by gluing pre-threaded acrylic blocks to the backs using an acrylic resin-based glue like Weldon 16.
I believe this is still the industry's "best practice" for cutout graphics.
The problem is that there are so many people in the sign industry these days who have never learned industry standards. There is a race-to-the-bottom mentality now, both in terms of materials and fabrication methods. Many of us feel pressured to compete with goofballs who are trying to reinvent the wheel, all in the interest of being low-bid. The result is the classic "you get what you pay for."
Of course, we can often cheapen a job and "get away with it," if that really is the overriding goal on a job. This is nothing new. We have all tried it. And not every cutout PVC letter is going to self-destruct. But is that a valid argument for deviating from accepted standards? Isn't it true that it takes only one failure to wipe out any cost savings? One of my mentors used to say, "You can do it right, or you can do it over."
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A word about stud-mounting.
There is a reason why the use of pre-threaded glue blocks has been standard procedure for generations.
When you drill and tap holes into the back of acrylic, you introduce thousands of micro-fissures, tiny cracks along the edge of the cut hole. These cracks are typically invisible, though you can often wipe the area of the cut with a solvent and they will become visible as the solvent tries to expand the fissures. As the acrylic ages, and movement is created by temperature changes, every hole becomes a prime spot for a potential crack, especially if a threaded stud is screwed tightly into the hole (a tight fit introduces a destructive stress called creep).
Prethreaded glue blocks completely eliminate this problem. and the labor-intensive drilling and tapping operation is avoided.
Think about this: there is a reason why acrylic faces are never held into lighted signs by screws or other penetrations. The fasteners make the plastic crack. Retainers, on the other hand, allow the face to float undamaged.
What if someone insists on heavy acrylic for cutouts? You can still install them with glue blocks. But what about glue failure? I've installed thousands of acrylic letters in the past 50 or so years. The ONLY glue failures were from acrylic that was not cleaned well enough, or from contaminated glue. Also, the few times I used heavy acrylic thicknesses for cutouts, I also used larger glue blocks when possible. Forcibly removing a properly adhered glue block should break the plastic before it loses its grip.
Brad in Kansas City
