Carving High Density Urethane Signage

High Density Urethane is an easy-to-fabricate, cost-effective and durable alternative to redwood and cedar for carved, routed and sandblasted signs.

By Jim Hingst @hingst_jim

Tips on Processing HDU

I think I shall never see

an HDU sign as lovely as one

carved from the wood of a tree.

So much for poetry. Joyce Kilmer I’m not. I’m also not a tree hugger and neither are most of the sign makers, who still carve.

Don’t get me wrong, I believe in all of the good things green, such as sustainability and conservation. Although I love trees, I also love to carve real wood. Nothing synthetic can match the natural beauty of wood’s grain and coloration.

Most carvers feel the same way. The irony is that the vast majority of them now carve high density urethane (HDU), instead of wood. While that sounds downright absurd, from the perspective of good sign business, it makes all the sense in the world.

In this story, I will cover the advantages of HDU and review some helpful carving and fabrication tips, that I learned, when I visited my friend, Sal Cabrera, at his shop in New Freedom, Pennsylvania.

Why High Density Urethane and Not Wood?

High Density Urethane sign board, such as Sign*Foam®, Precision Board® and Design Board®, is an easy-to-fabricate, cost-effective and durable alternative to redwood and cedar for carved, routed and sandblasted signs. Here are the key advantages:

Ease of Fabrication. Carving HDU is much easier than carving wood. When carving wood, you must be mindful of the grain direction or you will experience unsightly tear out of the wood. Not so with HDU, there is no grain, nor are there knots or pitch pockets. The material can be sawn with band saws, table saws and jig saws. Not only can HDU be sandblasted, but you can also use files, wire brushes, grinders, and wood carving chisels and gouges to finish the surface.

Because HDU doesn't have any grain, it is much easier to carve than wood.

Durability. While HDU may not have the strength of real wood, it is arguably more durable. Because High-Density Urethane Board is a closed cell synthetic material, it is impervious to water and humidity. What that means is that unlike wood, HDU will not

absorb moisture and for that reason, it will not swell, rot nor decay from the intrusion of water. It also won’t warp, check, split or splinter. Unaffected by changes in temperature, HDU is also a very dimensionally stable material.

Consistency. Many sign makers prefer High Density Urethane because the product is more consistent compared to actual wood. HDU may not have the grain and the knots that give wood its unique character, but not having grain makes HDU easier and faster to carve with hand tools.

Availability. It’s readily available in a variety of thickness: 1", 1.5", 2", 3" or 4". If you need a special thickness, you can easily cement individual pieces together to create monumental constructions. You can also fasten sections together with adhesives or with drywall screws, using fillers to completely hide countersunk screw heads.

HDU History

Not until the late 1980s did the sign industry discover HDU as an alternative for the dwindling supplies of redwood. Today HDU is the hands down favorite for hand carved and routed signage. Compared to wood, HDU is in many cases less expensive, easier to fabricate and it doesn’t rot, so it can last for years.

While it HDU has a relatively short history in the sign industry, polyurethanes have been around for about seventy years. A few years prior to WWII, the Germans started to experiment with polyurethanes in the lab. With the outbreak of war, commercialization of polyurethane products was put on hold.

Practical application of the science did not occur until the early 1950s, when HDU was used in the manufacturing of really important products, such as surfboards. HDU was a perfect substitute for wood. Not only, didn’t it rot, but it was lighter in weight, easier to fabricate and lower in cost. The foamed synthetic material was also comprised of millions of tiny bubbles or closed cells, which made it incredibly buoyant – great for surfboards.

NASA soon discovered that this foamed material was also great as an insulator and used it to cover the outside of their rockets. “If you have watched any space launches,” says Butch “Superfrog” Anton, “it’s the material notorious for falling off of the rocket as it lifts off.”

How HDU Is Made

To manufacture expanded polyurethane blocks, a volatile material called a blowing agent is added to the chemical formulation. These liquid polyurethane chemicals are poured into a mold, after which a chemical reaction begins, producing tiny, uniform bubbles of carbon dioxide gas. The foam bubbles create a closed microcellular structure.

The chemical reaction is finished within hours, after which the material is totally inert. That’s great news, because there is no outgassing which can bubble a paint job. Because HDU board is a closed-cell material, it is completely waterproof and resists solvents and other chemicals, which means it can be painted with traditional sign enamels.

The chemical reaction that occurs in making HDU generates a tremendous amount of heat, which is required to melt and polymerize the smaller molecules, forming a plastic of a much higher molecular weight. Because the heat generated in this chemical reaction is much higher than outdoor temperatures, HDU and other thermoset materials are very dimensionally stable and will disintegrate before they melt.

By comparison, thermoplastics, such as acrylic, polycarbonate, expanded PVC and styrene, can be reheated and remelted and are not so temperature stable and are more prone to expansion and contraction.

HDU can also withstand temperature extremes much more severe than encountered in even the harshest of climates. The service temperature ranges from -423° to 300° F (-252⁰ to 149⁰C). Manufacturers claim that the material will last in excess of thirty years, and longer if the material is processed and painted according to accepted industry practices.

After the chemical reaction occurs, the mixture solidifies and forms a very large block or slab of expanded polyurethane, called a bun. After the bun has solidified, it is cut into various thickness of sheets. Some of the standard sheet sizes for HDU board are 4' x 8', 4' x 10', 5' x 8' and 5' x 10' sizes, ranging in thickness from 1/4” to 20”.

Selecting the Right HDU Density

HDU is available in a variety of densities. By varying the chemical formulation, the manufacturer can control the degree to which the mixture foams and consequently the density of the sheet. Density is the weight of the HDU per cubic ft. The density ranges from 4 lbs to 45 lbs. Solid HDU, which has not been foamed, weighs approximately

68 lbs. per cubic ft.

In the sign industry the most common density is 15 lbs. The denser and heavier the material is, the harder and stronger it is and the more it can be carved in intricate detail. Denser 18 lb. sheets are sometimes preferred for hand carved projects.

As the density of the material in pounds per cubic foot increases so does the cost. The difference in cost between 18 lb. HDU compared to 15 lb. material can be as much as 30%. “While the difference in cost is significant, many sign makers don’t see a significant difference in product performance,” says Dino Giansante, General Manager of Proveer in Montreal, Quebec. “Although some of our customers prefer the denser material, 95% of what we sell is 15 lb. HDU.”

Sal Cabrera prefers using either the 18 lb. or 30 lb. material, which he buys from Harbor Sales in Sudlersville, MD. Sal prefers the denser, harder board, because it is stronger and holds finer detail better. While the denser material is slightly harder to carve than the less expensive and lighter weight 15 lb. HDU, the finished carving does not have so rough a texture. That’s an advantage, because it takes fewer coats of primer and consequently less production time to fill the rough texture of the HDU.

According to Cabrera, many sign makers select the raw materials based on price alone. “Sure controlling your costs is important for any sign shop,” Cabrera says. “But there are other considerations. The most important consideration is quality. If cutting costs compromises the quality of job, you haven’t gained a thing. Your customer won’t be

happy. And that can hurt your reputation. Your customer has lost and so have you.”

Storing HDU

How you store HDU is important. Leaning the HDU upright against a wall can cause the sheets to bow. If this happens, don’t panic. The bowing is easily remedied, according to Earl Mich’s Greg McKay by laying the sheet flat on a horizontal surface, such as a storage shelf or your shop floor. “If the sheets don’t return to their original flat stage,” McKay says, “you might have some bad material. You need to call your distributor and request replacement sheets.”

Duncan Covington, President of Harbor Sales, says that you can avoid problems altogether if you store your HDU sheets properly in the first place. “If you want it to stay flat, store it flat,” he advises.

              

Sign Design

You can layout your work the old fashioned way by hand. Although Sal Cabrera hand carves all of his signs, he uses FlexiSIGNPRO for most of his layout work. That way his design is precise. He can also nest the various sign components to maximize his material usage and reduce his waste. Sal feels that making the best use of his material resources is good for both the environment and his bottom line. Equally important, he has a computer file for his records, if he needs to duplicate the design at some later time. Carefully documenting the materials used, and the steps taken, also allows Sal the opportunity to review the project, when he has finished the job, and determine if there was anything that he may have done differently. In his project records, he not only details the manufacturing process in writing, but he also keeps a step-by-step photographic record.

After Cabrera completes his layout, he plotter cuts the individual components out in vinyl. After cleaning the HDU board with detergent and water, he applies the vinyl to it. Since Sal typically uses 18# HDU, the surface of  the sheet is smoother than the 15# material and the computer cut vinyl will stick to the board without priming. If you are using 15# HDU, you may need to prime the sheet, so the vinyl will adhere. The applied vinyl (see the photo below) serves as a template for cutting. 

Structural Support.

While signs made from HDU have a number of advantages over redwood and cedar, one disadvantage, is that it has neither the density nor structural strength of wood. As a comparison, the density redwood is about 27 lb. per cubic foot, which is nearly twice that of 15 lb. HDU.

Whereas wood is comprised of long, sinewy fibers, HDU is made up of very tiny cells – bubbles, if you will, that are formed in the chemical foaming process. These little bubbles don’t provide a lot of structural strength.

If a sign is subjected to significant wind load, you must support the HDU board in some way to strengthen the panel. Sign makers have bolstered their sign structures in many different ways, using a variety of materials. To give their signs added structural strength, they have sandwiched MDO, a metal framework or structured composite panels, such as Alumalite, DiBond, between two HDU sheets. While many sign makers will laminate a sheet of ½” MDO to either the back of a HDU board or sandwich it between two HDU sheets, Cabrera cautions that you could be asking for trouble. “MDO is wood. And if it warps, it can also cause the HDU to twist and turn,” he says. “In my opinion, you have better alternatives to MDO; Dibond and Alumilite are two good choices. They will give your sign the additional structural strength that you need to withstand strong winds without the warping of MDO.”

To sandwich a sheet of Dibond between two HDU panels, Cabrera . secures the sheet in place with dowel pins. He first drills three holes in the DiBond and in the HDU. The dowel rods stabilize the sections, keeps them from slipping and sliding out of alignment, while they are glued together. To ensure that the sign does not split apart at some time in the future, he spreads Gorilla Glue only in the center of the DiBond panel, keeping it several inches from the outer edge. To keep the Gorilla Glue from oozing beyond the edge of the DiBond panel, he applies construction adhesive around the entire perimeter of the sheet.

Cabrera will also incorporate a metal framework in his HDU signs for added structural strength. This framework is sandwiched between the two halves of the sign. He works with a local blacksmith, who manufactures his custom sign bracket designs and the framework. Working from a pen plotter drawing, the blacksmith can precisely reproduce the layout.

In routing channels on the back of a sign panel to accept a metal framework, Sal Cabrera recommends allowing enough space so that there is about a 1/16” gap around the metal (see the photo below).

To secure the framework in place so it does not slip during gluing, he adds dowel pins, which go through holes in the metal framework and into the two HDU sheets. Cabrera says that you normally do not need more than three holes in each metal bar. So that the sheets line up exactly, he uses “dowel and tenon centers” (see the photo below), which are available in a variety of sizes at Woodcraft. After you drill one set of holes, slip the centers into the holes. Then align the second HDU sheet over the first. Pressing down on the second sheet pinpoints the location, where you should drill your second set of holes.

After the dowel pins are inserted through the metal and into the HDU (see the photo below), Cabrera fills the gap around the metal framework with a two-part epoxy paste. “The epoxy is great for heavy-duty applications,” Cabrera says. “After it cures, it’s as hard a concrete.”

Before gluing the panels together, Cabrera recommends that you fit the parts together to make sure that the parts line up. To bond the two sheets together, he lightly mists the HDU panel with water and squeegees Gorilla glue over the surface using a piece of coroplast. Because the Gorilla glue expands, he never smears the glue to the edge of the sheets, instead allowing for a couple of inches of gap around the perimeter of the sign. Gorilla glue does not have the same texture as the HDU. For this reason, Cabrera prefers to leave a slight gap around the sign’s perimeter. After the glue dries, the gap is typically about 1/8” wide. He later fills this gap with either plastic wood or a two-part epoxy paste.

While many people will clamp the panels together as the glue cures,  Cabrera merely puts a heavy weigh on top of them. If the glue expands beyond the edge of the sheet (see the photo below), you should clean off the excess immediately.

Gluing HDU

When gluing sheets of high density urethane together using urethane glue,  tack the sheets in place with drywall screws to prevent them from slipping. Apply pressure on the boards using weights.

Sign makers use a number of different types of adhesives to bond pieces of HDU together. These adhesives include products such as Gorilla Glue, which is a polyurethane adhesive, and adhesives marketed by the HDU manufacturers.

Sign Arts Products, for example, sells their SIGN•GRIP™ adhesives, which are formulated to work with their SIGN•FOAM3 HDU products. Coastal Enterprises, makers of Precision Board™ HDU, also has a variety of adhesives, which include two one-part urethane adhesives called PB Bond, a 4 hour cure and PB Fast Set, a 30 minute cure.

Because HDU is impervious to many chemicals, some adhesives will not adhere to the closed cells over the long term. For that reason, before using any adhesive in production, always TEST, DON’T GUESS, and be sure to ask the manufacturer for recommendations prior to using it.

After mating the two surfaces together, use clamps or drywall screws to hold the pieces in place. Don’t use too much pressure, when clamping, or too much of the glue can squeeze out. Rest assured, some will squeeze out, so be ready to do some clean up. After the adhesive starts to set up, you can wipe away any excess adhesive that oozes from the joint with a damp rag. Any dried adhesive can be carved from the surface using a sharp wood carving chisel. If you use drywall screws to secure the sections while the adhesive sets up, you can fill the countersunk holes with bondo, after you have shaped the HDU.

Polyurethane glues, such as Gorilla Glue or Elmer’s Nano Glue, are great for bonding one piece of material to another, but be careful how you use it. As I mentioned before, these glues will expand as much a four times their original volumes. Because the glue foams up, it tends to get onto everything. For that reason, wear heavy-duty latex painter’s gloves to keep from getting it on your hands.

If you do get in on your skin, try washing it off with soap and water or Rapid Remover. Washing with solvent is not recommended. If the glue dries on your skin, there’s not much that you can do other than to wait a few days for it to wear off. Applying hand lotion sometimes can speed up the process.

Nevertheless, if you’re like me, you will manage to get it on yourself. So don’t wear your favorite work shirt when using this glue, because it will leave stains on your clothes that will not wash out.

Cutting, Carving & Shaping HDU

You can carve High Density Urethane using
the same type of tools that you use for carving
wood signs.

In cutting and shaping HDU, you can use many of the same types of power tools and hand tools that you would use, when working with wood. To cut out the general shapes of a design, the material fabricates easily using circular saws, band saws, table saws, jig saws and routers. Once you have the basic forms cut, you can use standard wood carving tools, such as chisels, gouges, knives, rasps and files. Because the HDU has no grain and no knots, it will cut easier than real wood.

Another handy tool to use to shape letters or other design elements is a spokeshave. “I frequently use a convex spokeshave to round the outside edge of dimensional letters,” says Chicago sign maker, Chris Maylone. Both convex and concave spokeshaves are available at Woodcraft or other fine woodworking stores (see the photo below).

For most projects, such as those that involve routing, carving or sandblasting, the 15 lb. density will suffice. If a job requires a more aesthetically appealing smoother appearance, you can always upgrade to the 18 lb. density, which has a smaller cell structure, and consequently a smoother texture.

After carving HDU with chisels, knives or rasps, you can use a variety of sandpaper grits, ranging from a coarse to fine grit, to smooth any rough edges.

In sawing HDU you can use a variety of power tools. Cabrera’s shop includes a table saw, band saw, and scroll saw. He also uses a jig saw for cutting out shapes. “If you use a jig saw, use one with fine teeth,” Cabrera says. “When I am cutting I take my time and cut at a slow speed.”

In the photo below, Sal cuts out the shape of an eagle using his scroll saw. He has applied RTape ProGrade™ paint mask directly to the HDU blank and uses it as his template. 

Regardless of what type of power equipment you use, sawing HDU or shaping it with a flexible shaft cutter or Dremel power tool can generate a cloud of dust. While the dust itself is not toxic, it isn’t good to breathe. Protect your lungs and sinuses and wear a well fitting dust mask and work in a well ventilated area of your shop.

Sandblasting High Density Urethane

On many of his signs Sal Cabrera will sandblast the background. Many sign makers, that use 15 lb. density HDU, will first prime and paint a panel, before applying their sandblast stencil. At the very least you should prime the board, otherwise the sandblast stencil will not adhere to the rough surface of the HDU. After the paint dries, the stencil mask is cut and applied to the board. In parts of the country, where the summertime humidity is high, drying can take days.

Sal Cabrera says that if you use the denser material, such as either 18 lb. or 30 lb. HDU, you can apply your stencil mask directly to an unpainted panel, after prepping the surface first by washing with detergent and water.

Sandblasting stencil mask is a pressure sensitive. You must use good pressure for it to adhere. How well it adheres also depends on the smoothness of substrate. For this reason, many sign makers will, at the very least, prime the HDU to smooth its rough cellular texture before applying the masking. Prior to priming the board, some sign makers will very lightly sand the surface with a fine 180-grit or 220- grit sand paper.

Using Anchor brand sandblast stencil mask from Harbor Sales, Cabrera sets his blasting pressure between 90 and 100 psi. In sandblasting, Sal Cabrera recommends that you keep the nozzle moving continually, working from side to side until you reach your desired depth.

In blasting the HDU, Cabrera recommends that you keep the blaster nozzle a couple of feet from the mask and keep the nozzle moving continually. Holding the nozzle stationary can blow the sandblast mask right off the surface of the HDU.

If he intends to fill the background with smalt, Cabrera generally will sandblast the background to a depth between 1/2” to 5/8”. This depth is necessary, because the combination of adherent and the smalts can be quite thick.

Sanding HDU Before Priming

After processing this materials, don’t expect it to be smooth. Machining leaves the surface with a semi-rough, sandpaper-like texture.

Before priming the surface, you will need to smooth the substrate using a 120 and 220 grit sandpaper. Sanding polyurethane foamboard can produce very fine dust that you may not see. Inhaling this dust can be harmful to your health. Always wear a multi-ply dust mask, when sawing or sanding HDU. If the weather permits, do your sanding, sawing and grinding outdoors.

Priming and Painting HDU

Because HDU is impervious to chemicals, you can use any type of paint to decorate it including enamels, urethanes and lacquers. Before painting, however, the surface must be primed.

Painting without priming produces a very dull finish, which for most signage projects is unacceptable. Many of the primers that sign makers use for HDU have very high solids content, which coats the board with a thick layer of primer, smoothing the rough texture of the HDU material.

Not all primers are the same. A standard primer only contains about 35% solids. Primers, such as Coastal Enterprises’ product is 80% solids. The advantage of the high solids primer is that it fills the rough sandpaper-like texture of the HDU surface.

Many different primers are suitable for HDU. These include Zinsser Bulls Eye 1-2-3, Jay Cooke’s All-Purpose Sign Primer and Chromatic High Build Primer (see the photo below). These three primers all adhere well to a wide range of sign substrates, including wood, metal, PVC and HDU, and are compatible with sign enamel, latex and polyurethane paints. In addition to these, some of the HDU manufacturers, such as Coastal Enterprises and Sign Arts Products, market their own brands.

Priming the HDU is important, because it anchors the subsequent coatings to the substrate and it provides a smooth foundation for the paint. With all of the choices on the market, you may have difficulty making a choice. My recommendation is to “Test, Don’t Guess”. Buy a quart of two or three primers and conduct your own test.

Sal Cabrera usually buys Zinsser Bulls Eye primer. “The Zinsser primer produces a good hard coating,” Cabrera says. “What’s more important is if I need primer, I can run down the local hardware store and pick it up the same day, instead of waiting on a delivery.”

Cabrera prefers a waterborne primer because it dries fast, which improves his shop efficiency. In as little as one hour, the Zinsser primer is often dry and ready for a second coat. With low VOCs, the waterborne primers are also more environmentally friendly.

Before priming HDU, you should sand the surface to remove and machining marks. Any inks used by the manufacturer to identify their product should also be sanded away, otherwise they will show through the primer.

After sanding the HDU, clean any residual dust from the surface using a brush, compressed air or a tack rag. You can apply the primer using a brush, roller or spray gun. When you apply the primer, don’t lay it on too thick. A thick coat will take longer to dry and can trap moisture that could lead to problems later. It is better to apply two thinner coats of primer, than one thick coat.

Either latex or oil-based primers can be used. When using a water-based primer be sure to allow enough drying time between coats. Water-based primers dry from the outside in. While the outside layer of the primer may feel dry to the touch, the inside layers of the primer may still be wet. By comparison, oil-based primers dry from the inside out.

When brushing on the primer, you may want to use an inexpensive bristle brush. “When I am coating HDU, I brush the primer on from various directions,” Cabrera says. “That way I can be sure that I scrub the coating into the rough finish of the carving.”

Using this technique, ensures that you work the primer into the cells. The primer manufacturers will claim that depending on the ambient temperature and humidity in your shop, drying should occur in an hour. Lot’s of luck. Since HDU is not porous, it does not absorb any moisture, in most cases, additional drying time is needed.

In extremely humid conditions, some primers will not dry for days. To speed up the drying process, you can direct a high volume fan at the coated boards. Air moving across the surface draws moisture from the primer and speeds curing time.

After the first coat of primer has cured, the finish of the coating will change from a gloss to a matte finish and will be dry to the touch with no tackiness. The HDU board is now ready for its second coat of primer. If the board is not smooth after this coating, a third coating of primer will be necessary.

The primed substrate must be completely dry prior to painting. Since HDU board has closed cells, it does not absorb moisture. The primer must dry by evaporation. Depending on your shop environment, this can take at least twelve hours and longer when the air is humid.

The most common mistake made when decorating HDU is not allowing the primer to dry completely before painting. If the primed board is painted too soon, the paint will trap any residual moisture. With no place to go, the paint layer frequently blisters when exposed the baking temperatures of the sun.

The best way to cure the primer is to get it time to dry naturally. Force drying the surface in an oven or putting the primed board in the sun to speed up the curing process can cause the primer to scale over trapping moisture underneath the dried skin of the primer, which can cause blistering.

Between coats there is no need to sand the substrate. Before painting, however, you will need sand the primed surface starting with 120 grit sandpaper, followed by sanding with 220 to 320 grit paper. If the primer isn’t completely dry, the coating will start to ball up on you. When this happens, just stop what you are doing and put the board aside until the primer has completely cured. In sanding, be sure only to sand the primer, avoiding abrading through to the HDU board itself. If you wet sand the surface, allow twelve hours for additional drying before painting. After sanding the primed board, wipe the surface down with a tack cloth.

Whether you are priming or painting, always coat the backside of the sign blank. If you only paint the visible side of the sign, the tension caused as the primer and paint dries and shrinks, can cause the board to warp toward the painted surface. Coating both sides creates even tensioning as the paint dries and shrinks.

After the HDU is primed, you can paint it with either enamel or latex paint. Be sure to dry sand between each coat, using a 320-grit wet & dry sandpaper. Sanding will smooth the surface, removing any imperfections and will promote good inter-coat adhesion.

Gilding

Although HDU can be painted with either latex or enamels, Sal Cabrera cautions “if you plan to do any gilding, you will get better adhesion painting with enamels than you will with latex paints.”

Cabrera also recommends taking the time to sand the HDU appliqué, as smooth as you can get it. “If you apply gold leaf to letters or scroll work with rough spots, the shiny gold leaf will magnify the imperfections and stick out like the proverbial sore thumb.”

Many sign makers paint the HDU with imitation gold before gilding. That way if you have a holiday, which is a void in the gilding, it will be less noticeable against the gold background.

Dr. Francis Lestingi of Signs of Gold in upstate New York believes that hiding the flaw just won’t cut it. “There is no way that imitation gold paint can duplicate the color and the magnificent brilliance of real gold leaf,” he says.

Instead of using imitation gold as the underpainting for the gilding. Lestingi recommends using black enamel. “I want to see the flaws in the gold leaf; not disguise these imperfections,” he says. “In my mind, it’s always better to fix your mistake, instead of hiding it.”

Lestingi recommends Le Franc’s 12 hour size. This slow size is ready to gild after about twelve to eighteen hours following application. The open time for working with this size is often days.

Before applying the size to the black incised letters, Dr. Lestingi very lightly sprinkles kaolin powder onto the carving. Kaolin powder is used in the medical field. It is very pure and will not contaminate the adhesive value of the size.

Using an artist’s mop brush, Dr. Lestingi dusts the letters with the powder to evenly distribute it over the painted surface. Any excess powder is then vacuumed off, leaving a very fine gray haze on the black painted surface. As the size is brushed on, the haze disappears. Any missed spots are easy to detect.

After applying the size, Lestingi recommends carefully inspecting your work and make sure that the size hasn’t puddled. Any excessive pooling of the size would drown the ultra-thin gold leaf.

When working with gold leaf, cleanliness is next to godliness. Your hands are usually contaminated with oils and sweat, which can act as an adherent for dirt. Here are three golden rules which you should observe religiously when gilding:

• Always wash your hands before working with gold leaf.

• Avoid touching the leaf. If you must, wear latex gloves.

• To transfer the leaf use a gilder’s tip.

About Smalt

An interesting finishing touch to a carved sign, is the addition of smalt. Also called smaltz or “osmalto”, smalt is crushed glass enamel or sand. Although sign makers originally used smalt more than one hundred years ago as a background for gilded dimensional letters, Sal Cabrera frequently uses it for his carved HDU signs.

According to Cabrera, the thickness of the adherent used along with the smalt, requires that you sandblast the background to a depth of ½” to 5/8”. The photo below shows Cabrera’s sandblasted York County Police sign prior to the addition of the smalt.

Traditionally sign makers would use smalt paint to adhere smalt the sign surface. Today a variety of other adherents are used. Cabrera recommends a mixture of 60% Nazdar 59000 series black ink and 40% 1 Shot black lettering enamel. Other sign makers combine 50% Smith’s Cream with 50% 1 Shot paint.

Pete Payne of Canadian Signcrafters also recommends Hold Fast Oil, which is available from his company. The Hold Fast Oil is mixed with 1 Shot lettering enamel at a ratio of two parts of the oil to one part paint.

The most inexpensive and most commonly used smalt is black, shown in the completed police sign in photo below. Smalt is also available in an array of colors. Cabrera usually buys his smalt from Canadian Signcrafters Supply (www.signcraftersupply.com) in Ontario, Canada.

Repairing Damaged HDU

You can repair damage to HDU in a couple of different ways. If you need to patch up any cuts on the surface of the board, your can do some touch up work with a knife grade filler. Coastal Enterprises (Orange, CA) makes their FSC-360WB repair filler for this purpose. Their filler, which has the consistency of putty, can be applied to the affected area.

You can also use Bondo, the old standby patch for just about every kind of surface damage. Bondo will stick to just about anything, if the surface is prepared properly.

Sal Cabrera, who is affectionately known by his peers as the “Gorilla Glue Guy”, recommends using a mixture of 80% HDU sawdust and 20% Gorilla Glue. “This mixture closely resembles the look and texture of HDU itself,” Cabrera says. “And it’s much easier to sand than Bondo, especially after it hardens.”

Any rough or damaged areas on the surface of the carving can be
smoothed over using 3M Bondo. 

Conclusion.

While nothing synthetic can match the beauty of real wood, HDU makes sense for most commercial sign applications. In today’s competitive business environment, it is a cost effective alternative and has eliminated many of the problems of natural wood. By comparison, woods, such as redwood or mahogany, are significantly more expensive. At as much as 27 pounds per cubic foot, real wood is also heavier, and because of its weight, more difficult to install.

If you haven’t done any carving, working with high density urethane is a good place to start. Carving wood can challenge beginner and pro alike. When carving wood with a chisels and gouges, the craftsman must always carve in the right direction. As the edge of the chisel cuts through the wood, it should always compress the fibers of the wood. Cutting against the grain opens the fibrous strands of wood, which can cause a split or tear out. With HDU there is no grain which can split open. HDU is much more forgiving. 

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Set of 5, 1/4 inch Shank, Ball Nose, Cylinder, Flame, Sphere, Extra Coarse Grit, Orange - End mill & Carbide Burr Kit by Saburr Tooth

Set of 5, 1/4 inch Shank, Ball Nose, Cylinder, Flame, Sphere, Fine Grit, Yellow - End mill & Carbide Burr Kit by Saburr Tooth

NEW INSTRUCTIONAL VIDEOS.  Five new videos have been added to RTape’s  YouTube channel. The following is a description of the new videos:

Squeegee Technique. Nothing is more basic in vinyl application than the squeegee. But some squeegees work better than others. And there are right ways and wrong ways to use this simple tool. This video clip reviews squeegee selection, squeegee care and squeegee technique. Click here to view the Squeegee Technique video.

Wet Applications. Dry applications are typically recommended for most vinyl applications. For those exceptions to the rule, this instructional video explains the right way to perform a wet application. Click here to view the Wet Applications video.

Introducing AT65. Installing multiple color overlays with a paper application tape is not much easier than driving in the dark without your headlights. For these challenging applications, RTape developed its AT65, the universal high tack film. This video clip explains the features and benefits of this remarkable new film application tape. Click here to view the Introducing AT65 video.

Application of Window Graphics. Installing vinyl graphics on glass can be challenging, because the adhesive aggressively grabs onto this high energy surface. Repositioning graphics on window is generally difficult, if not impossible. This instructional video explains how to dry apply window graphics right the first time. It also describes the necessary steps required for surface preparation. Click here to view the Application of Window Graphics video.

Transferring Frosted Window Graphics Films.  Because frosted window films are highly textured, transferring cut vinyl graphics can be problematic. This video provides direction in selection of the right application tape and how to apply these films quickly, easily and without problems. Click here to view the Transferring Frosted Window Graphics Films video.

About Jim Hingst: After fourteen years as Business Development Manager at RTape, Jim Hingst retired. He was involved in many facets of the company’s business, including marketing, sales, product development and technical service.

Hingst began his career 42 years ago in the graphic arts field creating and producing advertising and promotional materials for a large test equipment manufacturer.  Working for offset printers, large format screen printers, vinyl film manufacturers, and application tape companies, his experience included estimating, production planning, purchasing and production art, as well as sales and marketing. In his capacity as a salesman, Hingst was recognized with numerous sales achievement awards.

Drawing on his experience in production and as graphics installation subcontractor, Hingst provided the industry with practical advice, publishing more than 150 articles for  publications, such as  Signs Canada, SignCraft,  Signs of the Times, Screen Printing, Sign and Digital Graphics and  Sign Builder Illustrated. He also posted more than 325 stories on his blog (hingstssignpost.blogspot.com). In 2007 Hingst’s book, Vinyl Sign Techniques, was published.

© 2015 Jim Hingst