Properly applied, a painted MDO (medium density overlay) sign can provide up to 10 years of service life or more. Premature paint failure often occurs for a variety of reasons. Often problems develop because the surface was improperly prepped. Using the wrong raw materials for the application or incompatible materials can also contribute to problems. 

Of course, the durability of the painted surface is not solely dependent or the responsibility of the sign painter.  The environment greatly affects durability. Signs subjected to a great amount of sunlight and moisture will deteriorate much faster than signs that have great protection from the elements.

If you have not worked with MDO before, the tried and true tips from veteran sign painters should help you do the job properly and profitably. A number of years ago, Butch “Superfrog” Anton in Moorhead, MN shared the secrets to his success in working with MDO, and I would like to share them with you.




































Edge Preparation. Like any other plywood product, the most vulnerable parts of the sheet are the edges.  If the edges are not sealed properly, the sheet will absorb moisture, which will lead to paint failure on the surface of the board. Moisture can also cause delamination of the plies.


Paint tends to chip where there are any sharp edges. To minimize chipping, some sign makers will run a router with a ¼” rounding over bit along the sides of the sign to take the edge off of the edge. 

All voids on the edge of the board must
 be filled completely and sealed properly.


Make sure that any of the voids on the edge of the board are filled and sealed properly. If you don’t, water will seep into the core of the board, causing the sheet to deteriorate.  To fill these voids use a caulk sealant, such as GE’s Max 3500 Siliconized Acrylic Latex Window & Door Caulk (available in either white or clear), DAP® Alex® Painter’s Caulk, and Liquid Nails Acrylic Latex Caulk. 

“I use a siliconized paintable caulk called Alex Plus, which I buy at Wal-Mart,” says Butch Anton.  “I always buy the clear caulk. When you first apply it on the edge of the board, it appears white. After the caulk dries, it turns clear.  This tells you that the caulk is cured and you are good to go.”

Before applying the caulking compound, make sure the edge of the board is clean and dry. Cut the tapered part of plastic tip of the caulking tube at about a 45° angle to the match the size of the bead desired.  Using a standard caulking gun, apply the caulk to the edge of the board, making sure that the caulk completely fills any voids. After applying the sealant along the edges of the board, use a squeegee to smooth the caulking. 

“I cut a ½” notch in the squeegee to match the thickness of the board,” Anton says. “With good, firm pressure I smooth the bead of caulk forcing in into any crevices, so all of the voids are completely filled. The sealant usually dries in fewer than four hours, depending on the heat and humidity in your shop, after which it is ready to prime and paint.   I paint the edges at the same time that I paint the face and the back of the board.  This will put two to three good coats of paint on the edges.”

Some manufacturers will caution against using a latex paint on the edges.  Compared to oil-based paints, a latex paint is comprised of much large molecules. The spaces between these large molecules make a latex paint porous.  As a house paint, this is a good feature, because it allows moisture in a wood substrate to escape through the paint.  When sealing the edges of plywood, though, this may not be a benefit, because it can allow moisture to penetrate through the latex paint and into the wood. For this reason, many experienced sign makers prefer using oil-based enamel paints.


MDO sign for my grandson's 3rd birthday party.


The overlaid area of HDO or MDO protects the plywood from moisture. The parts of the board that are most vulnerable are the edges. In prepping the board, sand the edges and the corners with 120-grit sandpaper. The edges don’t need to be perfectly smooth. Leave them slightly rough so they have some tooth for the paint to stick to. If the paint fails on the edges, the board will absorb moisture and the sign will fail.


Priming & Painting. Sign makers have used many different types of paints and developed a variety of procedures for coating out MDO.  While coating out the background of a sign may seem rather prosaic and blasé process, it is critical in producing a durable product. After all, if the background paint blisters, chips or peels, the whole job is a failure.


Sign painters will prime and paint MDO with a variety of types of paint.  Many have switched to using water-based paints.  These paints dry faster than oil-based products and there are no noxious fumes.


On the other hand, many of the veteran sign painters, such as Butch Anton, prefer the oil-based paints.  Some of the complaints about the water-based paints include problems in adhering vinyl graphics to the painted surface. Another common problem with latex paints is that heavy coatings may not adhere well to the substrate and pull off as you remove application tape following vinyl application. 


There are always two sides to a story. Proponents of water-based paints feel that there is nothing wrong with latex paints on wood surfaces.  After all, acrylic latex is used to paint houses and can provide up to ten years of outdoor use.  What gives latex paints such excellent durability is that the acrylic binder, which is a key ingredient in these paints, forms a very tight bond to wood surfaces. This bond help prevent paint failures, such as peeling.


When coating out an MDO panel, the most important coat of paint is the primer.  To reduce the time that it takes to coat out a board, some MDO are available already primed, either one or two sides.


MDO plywood signs should be painted with a primer such as Ronan Block Out White, and then with two coats of 1-Shot enamel. Lightly sand between coats of paint using a 230-sand paper to ensure good intercoat adhesion.  Thinning the enamel will help it flow out. However, the more you thin paint, the less pigment is coated on the substrate and consequently the durability of the finish is shortened. Applying thicker coats of paint will deliver longer outdoor life.


For a durable exterior sign, coat the MDO 
with two coats of primer and three finish coats.



Even though sign makers often buy preprimed MDO, many veteran painters prefer coating out their own boards.  “The priming on the preprimed board is usually pretty cheesy,” Anton says. “To produce a durable sign, I apply two coats of primer and three finish coats.”


“After 30 years as a sign maker, I have done extensive tests and studies of different types of primers and paints on MDO,” says Butch Anton. “I, for one, do not recommend priming MDO with a water based product.  The most common failure that I have encountered over the years involves the delamination of water-based primer from the fiber overlay.”


Anton recommends first scuffing the fiber overlay with 220-400 grit sand paper. Lightly roughing up the surface of the MDO board with sandpaper gives the paint a better chance of adhering. After sanding, wipe down both sides of the board with a lint-free rag, followed by wiping with a tack cloth. 


The sanding is intended to eliminate the grain of the wood from showing through the overlaid fiber sheet. The fiber overlay can be applied to either one or two sides. The smooth fiber surface is impregnated with a special resin, which is designed to accept paint.  If the panel is properly primed and painted, it should deliver exceptional outdoor durability. In fact, a painted MDO panel should easy outlast painted exterior grade plywood. 


The key to any good paint job is the primer.   Although many sign painters today are using water-based primers, in the opinion of many of the old veterans, you are much better off using an oil-based product.


In priming MDO, Butch Anton thins his background color, which usually is a One Shot or Ronan enamel at about a 50:50 mixture of paint and thinner. 


While many sign makers use a foam roller, Anton prefers using a short nap fuzzy roller to coat out his sign boards or he sprays the primer coat. After the primer coat dries overnight, he scuffs the surface with a fine grit sandpaper and then repaints the substrate with One Shot or Ronan without thinning.

 Once the background is painted, the sign
 is ready for decoration using lettering 
enamels or applied vinyl graphics.
Although you could get by with one coat of primer, two coats of primer are always better, followed by two finish coats. In selecting paint for the finish coats, always test the primer and top coat for compatibility or use a paint and primer from the same manufacturer.  Always follow the manufacturer’s recommendations regarding surface preparation, ambient temperature, thinning, paint application and drying times.



If you use good quality materials and follow the Superfrog’s tips, your signs can last ten years and more.

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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.

Slides of Jim's Artwork

© 2015 Jim Hingst






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