Using Hardboards for Sign Substrates

A sign maker asked if he could mount a printed vinyl graphic to Masonite, which is another name for hardboard. Because hardboard is porous, we told him to either paint or varnish the sheet to prevent it from absorbing moisture which could adversely affect the adhesion of the graphics. A better answer is to use a product called Scooter Board which is a hardboard with a water-resistant urethane coating. (We'll tell you more about Scooter Board at the end of the article.)

"For most outdoor sign applications, hardboard is a poor choice if you want a long lasting sign," says pinstriper John "Tramp" Warner of One Shot. "The best for hardboard is indoor signage and cut outs for wall graphics. I only use tempered hardboard. I buy it already coated out. Then I scuff it, wipe off the dust and give it a coat of One Shot. It's like glass to work on."

Even though a board may be coated, Warner advised to recoat it with 1-2 coats of One Shot lettering enamel using a foam roller. This extra step prevents the background from fading out. "Recoating your boards ensures that your sign will last in the elements. If you don't recoat your board, they're likely to turn brown within three years. As I like to say, there are no shortcuts to quality and value."

What's in a Name?

What most people call Masonite is more correctly called hardboard or hardwood board. Masonite is a brand name of the Masonite Corporation for a hardboard product, appropriately named for the person who invented this type of hardboard in 1924, William Mason. Although the name is still used and the company is still around, the Masonite Corporation closed its hardwood manufacturing plant in the United States a couple of years ago. Masonite may not be available but similar hardboards, such are Duron, are still on the market.

To set the record straight, and give credit where credit is due, hardboard was actually invented nearly thirty years before Masonite was developed, in the late nineteenth century. Englishman Daniel Manson Sutherland is credited with the invention. However, the fickle finger of fate favored Mason over Sutherland. Because Masonite was the first brand on the market in the United States, the name stuck.

Mason made the original "Masonite" hardwood boards by subjecting wood chips to steam. After softening up the chips with steam, the wood is shredded so only the fibers are left. The slurry of fibers is spread over a screen, which helps drain the water from the mush. The remaining water is squeezed and baked out of the sheet in a press. In this process, temperatures reach at least 350ºF. This high heat not only turns any water to steam, but also fuses the ingredients together. Because the original wet process hardboard is made on a screen, the sheet is smooth on one side (S1S). The other side of the sheet has a rough texture. The wet process hasn't changed since the days of Mason.

The original wet process "Masonite" panels used no glues or resins to bind the fibers together. The product was completely natural and only uses the raw cellular material in wood itself. By today's standards, wet process hardboard is "eco-friendly." Wood fibers are composed of cellulose which comprise the cell walls of wood and a material called lignin, which is a binder that hold the walls of a cell together.

After soaking the wood fibers, the cellulose and lignin are reconstituted into a sheet. No other binders are added. Only the lignin of the wood fuses the fibers together under heat and pressure. As the hardboard is pressed, water is forced from the sheet, and the board is squeezed to the desired density and thickness.

The long wood fibers of hardboard give it strength. The strength also comes from the fact that the fibers are not oriented in any particular direction. Rather, the fibers are pressed together randomly. That intertwining of fibers does a better job of holding the sheet together than if the fibers were arranged in a single direction. Nevertheless, as strong as hardboard is, it does not have sufficient structural strength for many building and signage applications...certainly, no where near the strength of plywood.

These sheets derived the name "hardboard" because the manufacturers use hardwoods such as oak, aspen, maple and birch to make the panels. "The name 'hardboard' is well suited," says Jim Graham, President of Woodcraft Manufacturing Co. "It's one hard board. Although it's made from wood, it's more dense and a lot tougher. It's tougher to saw, tougher to drill and tougher to nail." Some people may view that toughness as a shortcoming. Graham feels that hardboard's toughness is it's best attribute.

While hardboard is made from wood, it doesn't have all of wood's characteristics. There are no knots, grain, sap, and no variations in strength and consistency from one tree to another. Compared to wood, hardboard is generally more resistant to moisture, its surface is smoother, and is more resistant to impact. Its uniform density also makes it less prone to warping.

Conceivably, hardboard could be made from any type of plant material. So why not use cheaper, more abundant and easier to process pine? Graham says that the reason is that softwoods contain high amounts of resins that can stain a painted surface. Softwood fibers are also softer and tend to crack.

The wet process isn't the only way to make hardboard. "Later a dry process was developed," says Graham. "There's also a wet/dry process. Each manufacturing process is different and the finished products are different too."

Along with developing a wet process for making his Masonite, Williams Mason invented a wet-dry process. Both processes are similar. In the wet-dry process the wet mat of fibers is pre-dried before the sheet is pressed. Temperatures are also higher, reaching more than 400ºF. The end result is also different, because this process produces a board with two smooth sides (S2S).

As the name suggested, dry process hardboard do not use water in manufacturing. Instead, wood fibers are dried and fluffed up. Dried fibers are blown into a large box to form a thick mat. To help bind the fibers together, synthetic additives are added to the mix.

As the wet process arranged the fibers of a sheet into two dimensions, one layer of fibers on top of another, the dry process arranges fibers randomly in three dimensions. To make a board with two smooth sides (S2S) the fibrous mat is squeezed in a press between two hot plates.


To toughen the hardboard up a little, manfucturers added resins, waxes and other goodies, such as oil. The oil acts as a binder which makes the sheet stronger and more resistant to moisture. Sheets without additives are called "untempered." Hardboard with these additives are called "tempered." Regardless of whether a hardboard is manufacturered wet or dry, the sheet can be "tempered."

In the tempering process, the boards are heat treated. Subjecting the board to heat creates a stronger bond and further compresses the sheet. Tempering the hardboard harden the surface, making the sheet more resistant to abrasion and scratches and less prone to warping. It also makes a more dimensionally stable sheet which is also more resistant to moisture.

Painting Hardboard

In the manufacturing process, oil (such as tung oil) is applied to the surface and then the sheet is baked in a recirculating oven. The oil slightly penetrates the surface of the sheet and what is left is flashed off the bake cycle. Contrary to popular belief, no oil residue remains on the board. So there's no surface contaminant to cause paint adhesion problems.

"Treating the board with oil makes the sheet more printable because the treatment improved the hold out of the paint," says Jim Graham. "Otherwise, the board would soak up the paint like a sponge." The term "hold out" means that the finish coats of paint do not soak into the primer of the board itself. Poor paint hold out results in an uneven blotchy finish.

 If you are going to use hardboard as a sign blank, you need to treat it with a little TLC if you want it to last. Here's how. Before you do any sanding and painting, you must clean the hardboard. "Never clean hardboard with detergent and water," cautions Graham. "Water will just raise the grain of the sheet."

To prep the surface of the hardboard, Graham recommends either wiping the surface down with a clean rag or tack cloth, quickly wiping the surface with a rag damped with a solvent. Take the time to clean the surface properly. Poor surface preparation is a leading cause of paint failures.

After cleaning, the next step is to lightly sand the smooth, glossy side of the sheet using 600 grit sandpaper. Scuffing up the sheet will give the surface some tooth for the paint to bond to. Failure to sand the smooth, hard surface can result in paint adhesion failure. Next, take a damp cellulose sponge and wipe off any dust and particles.

You can paint hardboard with either an emulsion or oil based paint system or with lettering enamels. If you are using a sign enamel, such as 1-Shot Paint, you can prime the sheet with thinned lettering enamel. With other oil based paints use the manufacturers recommended primer. When using an emulsion paint you can also thin an exterior grade paint with water at a 1:1 ration and use that as a primer.

Regardless of which paint you use, prime the surface with at least one coat of primer. Priming is an absolute necessity. Failure to prime the surface can result in the wax in the board bleeding through and yellowing the finish coat of paint. Don't forget to prime the edges and the backside of the board.

After priming, lightly scuff the surface with 600 grit sandpaper and finish the job with 1-2 coats of paint. If you are using an emulsion or water based paint system, we recommend applying two coats. If you are painting with an oil-based paint, coat the rough backside of the sheet to prevent bowing the board.

If the sheet is used for outside application, be sure to coat the edges of the board to prevent moisture absorption. Coating the backside of the sheet is always a good idea for exterior applications. Failure to do so may result in moisture penetrating the sheet to the paint layer. Moisture under the pain will cause peeling.

The Next Generation

Have you hard of Scooter Board? It's the next generation of hardboard. Jim Graham decided to improve on the Masonite formula. Graham, who's father worked for the Masonite Corporation, well understood the pluses and minuses and decided to make a good thing even better.

"We use the same 'wet process' in making the board as Masonite did," says Graham. "In fact, we're the only company that is using the old process. But to improve the stability of the sheet, we made a few changes."

In processing, the raw materials are broken down into shorter fibers. Graham feels that the shorter fibers are less prone to absorbing moisture and less prone to warping than the earlier generations of hardboard.

The major difference between Graham's product and the original hardboard is that Scooter Board™ is surfaced with a white urethane. The plastic covering is fused to the hardboard core using heat and pressure. The surface of the sheet is pretty tough. It resists water, solvents and mild acids.

Scooter Board™ is great for screen printed signage, but you have to use the right ink. Ask you distributor for an ink recommendation. Graham recommends several Nazdar inks, including the 5900 series enamel inks with no catalyst and either a 9600 or 9700 series with a catalyst. Nazdar's 1700UV inks are also recommended.

The surface of Scooter Board™ is tough to stick to. Nazdar makes two catalysts for their inks. NB72 and NB80, which can improve ink adhesion. For outdoor applications, mix 5% to 10% by weight of the NB80 catalyst with the 9600 and 9700 inks. After the catalyst is added, shelf life of the ink is limited to about four-to-six hours.

Bea Purcell, former Market Segment Manager for Nazdar (now retired), says that the catalyst can slow curing. For that reason, "if you are printing multiple colors, make sure that the first coat is thoroughly cured before printing subsequent colors," says Purcell. Nazdar's NB72 also improves adhesion, but it's only for indoor applications. Purcell says that exposure to UV light can yellow ink that has been mixed with NB72.

Before screen printing, read the ink manufacturer's technical bulletins and 'test, don't guess' prior to production. Typical tests are a cross hatch test, tape test and scratch resistance test.

While the original Masonite may have had problems enduring the elements, Scooter Board™ is ideal for many outdoor signage projects. "We originally thought that Scooter Board™ would be an excellent alternative to aluminum for real estate signs," Graham says. "Unlike metal, our product doesn't dent."

Sign makers soon found other applications for the product, such a point-of-purchase displays, trade show graphics, event signage and election signs. As well as being an excellent choice for screen printing, it's also an ideal substrate for applied vinyl graphics and digital prints.

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