High-density urethane (HDU) is a great material for creating carved, lighter weight dimensional signs. However carving is only half the job; the other half is decorating and finishing the material.
Know Your Products
Painting is the most common way to decorate an HDU sign, and shops have a variety of coatings to choose from— including everything from acrylic to oil-based and even specialty finishes.
“Most types of HDU are compatible with almost any type of primer, coating, or paint,” says Brad Burnett, HDU sales representative at DUNA-USA. “These can include hard coats, faux metal finishes, and even customized patinas.”
But the process isn’t as easy as brushing or spraying some paint onto HDU.
In fact, Mike Szczoczarz, owner of Countryside Signs in Seekonk, Massachusetts, says the most important thing before getting started is to know your products.
“You have to know the products before you can do anything correctly,” he says. “If you have failures, a lot of it is self-inflicted.
“People want to blame the material or the paint, but most things are self-inflicted because you haven’t paid attention or you haven’t learned the material.”
Szczoczarz recommends contacting your HDU manufacturer for samples and then experimenting with those samples and the different methods of painting.
“It’s a matter of knowing how to handle the different types of paint and your end use,” he says.
Keep Things Clean
It’s critical to know that end use or intended final result before starting, since it will impact the steps and the process you take to get there.
No matter what type of result you’re going for, the HDU must be cleaned. It’s important to keep it clean from the start, since dirt and contaminants can easily become trapped in the material.
“Keep the HDU clean from grease, oils, and contaminants because you can’t really wash the grease or contamination off of HDU very easily,” says David Bly, technical manager at AkzoNobel.
From there, it’s important to get any debris from routing and carving off of the material.
“The best method is to use an air nozzle and ensure that all dust and debris have been removed prior to finishing,” says Burnett.
Applying Primer
Once the material is clean, primer is applied next.
Not all projects require primer—this is where knowing the final result becomes important.
If your sign’s finish doesn’t need to be smooth and will have brushstrokes to achieve an effect like wood grain, then priming the substrate isn’t a necessary step.
However if you’re looking to achieve a very smooth finish, then primer is a necessity, in order to fill the cell structure of HDU and give you something to sand down.
Bly says two to three coats of primer are typically necessary, but it depends on the weight of the HDU.
“In general, going up in density will almost always result in reduced labor for priming and painting,” says Burnett.
This is because a higher density HDU has smaller, more tightly packed cells and less pores. A lighter weight HDU will take more primer to fill.
To apply primer, Bly strongly recommends using a roller versus spraying.
“If you’re trying to spray it with a spray application, you have to, in effect, flood the primer on until it floods into the pores,” he says, noting that 20 to 30 percent of the primer is lost when using a spray gun because it blows out into the air. “With a roller, you’re at a hundred percent of what they call ‘transfer efficiency.’
“So all the primer you use, you’re 100 percent transferring it onto the surface with a roller, and you’re pushing it into the pores instead of trying to flood it into the pores.”
Overall rolling on the primer leads to a more consistent application, cost savings, and environmental benefits, since the emissions and waste are much less (if not eliminated entirely).
Once you’ve completed the priming, the HDU should be allowed to dry overnight at room temperature, which is 65° to 70°F.
It can then be sanded to a smooth finish. Be sure to blow or dust off any resulting dust and debris before beginning the painting process.
Brush or Spray Gun?
Depending on your intended finish, paint can be brushed or sprayed on.
Spraying on the paint will lead to a smoother, high-quality finish. Brushes can also be used for smooth finishes in addition to effects, as mentioned above.
If using brushes, Szczoczarz recommends consulting the manufacturer’s recommendations for how to brush on the paint and which brushes to use. As a rule, higher-end brushes will give you a smoother finish.
“Use the best ones that you can afford and take good care of them,” he says.
What Paint to Use?
As for which paint to use, the choice is again related to the intended result. Szczoczarz goes over the three main types of paints sign shops use:
1. Acrylic Polyurethanes. These types of paints provide a high-quality, automotive finish.
They are the most durable and offer the greatest longevity, color retention, and color-matching options.
However it’s recommended to spray these paints, so sign shops will need to be set up with the capabilities to spray (spray equipment, a dedicated area to spray, etc.).
Because of the automotive-like finish, the signs can even be washed just like a car, which further extends their life.
Matthews Paint, AkzoNobel, and Sherwin-Williams all offer acrylic polyurethane paints.
2. Latex. These water-based paints provide a much more versatile method for sign makers who are entry level or don’t have spray capabilities. The paints provide good color retention and can be brushed or rolled on.
However sign makers have less time to work the paint.
“Latex can be tricky to master,” explains Szczoczarz. “You don’t want to overwork the paint, because it starts to set quickly.
“As the surface is drying, you actually may be picking up what was starting to stick. So you don’t want to let that happen, becaus that can lead to some failure.”
Szczoczarz recommends putting this paint on in heavy strokes with only two or three strokes.
These types of paints include house paints like Benjamin Moore and California Paints, and they come in a wide range of prices and quality levels.
As with brushes, Szczoczarz recommends using the highest quality paint you can afford.
“You can’t use a cheap paint and expect it to do what the best paint will do,” says Szczoczarz. “The thing is, with the lesser grades, you’re not going to get good coverage, so you’re going to be painting more. You’re not going to get good color retention.”
3. Oil-based. Oil-based sign enamels, like 1-Shot and T.J. Ronan Paint Corp., offer a long-lasting, high-gloss finish.
The paint can be applied using brushes or high-quality foam rollers.
Since the paint takes longer to set, sign makers can continue to roll or brush it on for up to five to ten minutes.
Ask for Advice
There are many finishes and effects possible when painting HDU.
If you still have questions, contact your paint or HDU supplier for direction.
By Ashley Bray
All photos: DUNA-USA.
