Steve and I both write for the same magazine, Sign Builder Illustrated, and he asked if I would mind laying out the basic procedures for making sandblasted signs. Heck - no problem! I'd love to talk about the work I enjoy so much, but always invite questions and comments, as this will have to be pretty once-over lightly in the space we've got. At some point I may bring out a book, but - heck, I still seem to learn something from each sign, and from all the friends I meet in the sign industry.
I love 3-D natural wood signs, whether sandblasted or carved - and customers as well as businesses have found them to be attractive and friendly. Don't be intimidated - you can provide some beautiful creations, often without having to do the production yourself.
Sign blanks are available widely. Perfect Plank in California, All Wood Sign Blanks in Vancouver, and Baltek Corporation - among many others - can provide high quality sign materials in redwood, cedar or balsa wood. If you choose to make your own blanks, the usual wood of choice would be either redwood or cedar, since "red" woods are easily worked and have some built-in natural resistance to insect or weather damage. Other wood types can be used, and true mahogany is another long-lasting variety. It's better to use narrow planks than wide ones to glue together, to avoid the cupping and warping problem common to wooden signs. For the same reason, alternate the direction of the grain patterns when matching planks. Most lumber has a "nominal" size, such as 2" x 6", which is not the same as the actual dimension - which in this case would be sold to you at about 1 5/8" x 5.5" after milling. I normally use 2" x 6" (nominal) boards when gluing up a blank.
Match your planks for grain structure and straightness, then glue together using a waterproof adhesive such as Resorcinol, Tite Bond II, epoxy or Sign Life's Ultra Bond. Inserting dowels or plate joiner "biscuits" help strengthen your creation, and keep the planks aligned during gluing. Any additional bracing you can add to the back, etc., improves your chances of a long-lived sign. Use plenty of adhesive, so there is some "squeeze-out" when you apply pressure. The usual clamps would be 3/4" adjustable pipe clamps, spaced about 10" to 12" apart, alternating from top to bottom as you go along. This keeps your blank from bowing under pressure of the clamps.
When dry - usually overnight - plane and sand smooth. It's usually best to seal the surface with something like a lacquer sanding sealer. I happen to use Sign Life's FIRST STEP, which saturates and strengthens the surface fibers, and gives a solid base for your blast mask.
The key to sandblasted signs is the availability of "resist" - a thick, flexible masking material which self-adheres to the wood, protecting covered areas from erosion by high-pressure sand during the blasting process. This was developed for and is still used by the cemetery monument industry, so if you have a problem finding a supplier, check out their source. Your local sign product supplier should stock material from Hartco, Anchor Continental or 3-M, all of them good products. I normally use Anchor's #117 (medium tack adhesive) for computer cutting, or their #125 for hand cutting. You can generate graphics and cut on a normal vinyl plotter, by using a 60 degree blade with pressure around 300 grams - or you can apply the blank rubber to your future sign and cut out any design or text with an X-Acto knife. For computer graphics, apply a high-tack transfer tape to the cut material, without weeding anything except material outside the borders. Then turn the sheet face down, and peel the backing material off steadily and carefully. Apply the mask to the wood, and apply pressure ( I usually do this with a 2" wide wallpaper roller). Then weed away all excess. If you have a problem, it's fairly easy to realign small portions by hand, or to patch as needed. Here, an extra step can save you a lot of grief - go back over all of the masking material with a heat gun and the pressure roller, to really squeeze the adhesive into the wood. This will help prevent it blowing off under the tremendous pressures created during blasting. At this point, you're probably almost ready to sandblast. Protect any vulnerable edges, etc., with something like a layer or two of duct tape.
Now - sandblasting! If you're not set up to do this yourself, someone in your area probably does commercial blasting. Hopefully they have some experience in wooden signs, but in any event, make sure that they use no more than around 80 to 85 PSI when blasting. The usual abrasive is simply silica sand, in a grit size between 30 and 60. (Glass work is done with grit size between 150 and 200) Keep in mind that silica sand is definitely NOT a good thing to inhale a lot of, nor is redwood sawdust, for that matter. Always use a dust mask, even if sandblasting within an enclosed cabinet. If freeblasting outside, much heavier-duty breathing/eye/skin protection is recommended. For those who want to use high-density urethane instead of wood, blast at a maximum pressure of 45PSI. HD urethane, by the way, is an excellent product, with superior resistance to weather damage.
After blasting to an appropriate depth, probably between 3/8" to 1/2", you can remove the masking material. Be a little careful here, as pulling against the grain can sometimes cause peel-up of some wood fiber. If you find that happening, try pulling from the other direction. This is one reason for having sealed the surface prior to applying mask. Incidentally, you can pre-paint the surface also, provided you let the paint dry for several days before putting on the sandblast resist. If you do so, you can now paint the background before removing the masking material. (If you experience paint peel-up, one method of preventing it in the future would be to first apply a layer of transfer tape to the surface before the masking resist.)
Shape your sign as desired, preferably routing edges for a professional, pleasing look. One of the beauties of wooden signs is the ability to create almost any shape in the world. Most signs are painted, though it is a shame to cover up the natural look of the wood. Unfortunately, the wood will change color if not protected, and a single color of unpainted wood will not be adequately visible to do its job of conveying information. Then, too, there are no varnishes or clearcoats available that will last for extended periods of time outdoors, where the elements and UV light eventually destroy them. Use the best stains and paints available to you - whether you use water or solvent-based materials - over at least one coat of good, dependable primer which should also be designed to "stain-block", or prevent the red colors of the wood from seeping through the finish. When mounting, allow some play in the installation bolts so the panel can flex with changes in moisture and temperature (wood can change size by up to 20% from day to day!), and allow some ventilation behind panels if wall-mounting.
Now - you're not a carpentry shop and not a sandblasting shop? Well then, you might want to have your design ideas translated into beautiful signs by whatever sign wholesaler you have available to you. (My own business is probably 75% wholesale for companies not equipped to do their own work, and the resulting signs have been shipped all over the world!) Regardless, your concepts and graphics can easily be turned into beautiful, 3-D works of art that adorn your favorite customers, whether you do all of, none of, or part of the work yourself. This is a very profitable and creatively satisfying branch of the sign industry, and I guarantee you'll thoroughly enjoy having these friendly creations working in your area. If you'd like more information, call or E-mail me anytime - or check out Sign Builder Illustrated's web page at www.signshop.com. My column, THE BLASTING BOOTH, runs under the "How-To" section. In an effort to attract advertising dollars, they offer a limited number of free subscriptions to legitimate sign shops through an effortless sign-up sheet on their home page.
Hope this guide has been a bit of help, and that you'll give sandblasted signs a try. Hope to talk to you soon!