“Cuckoo Chalet is 20-lb. HDU, hand carved, a couple coats of Dura Build primer, lightly sanded with a Scotchbrite pad, base painted in Matthews,” says John Ralph, Quail Run Signs, Hamilton, Virginia, ”and then glazed/distressed with 1-Shot with 4007 hardener added (which we always do). The letters are acrylic, painted with Matthews paint.”
“When we go the whole nine yards for a perfect finish, we prime with FSC-88, sand, then Dura Build primer, scuff and finish with Matthews paint,” says John Ralph, Quail Run Signs, Hamilton, Virginia. “It really achieves an amazing finish.”

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How others finish HDU board

By SignCraft Magazine

Posted on Tuesday, May 3rd, 2016

John Ralph, Quail Run Signs, Hamilton, Virginia, suggested we ask Trade Secrets readers how they handle some of the processes sign shops use every day. It’s a great idea and a great way to learn from each other. The first question was “How do you finish HDU board?”

We received many excellent responses and want to share some of them here. As expected, everyone has a little different spin on finishing HDU board. You’ll see the primers, finishes and the processes they use here. We hope this will help you produce HDU signs that are durable and look great, too.
Here’s what we learned:

We use three different approaches, depending on the look we want and the HDU we’re using. For a smooth finish, we use a high build acrylic primer followed by an automotive primer, then sand and finish with Matthews polyurethane paint. If we’re finishing with 1-Shot enamel, we’ll skip the automotive primer because 1-Shot is heavy-bodied and fills more. For something that has texture, we’ll shoot a coat of primer on it then finish it without sanding.

We use two different primers for HDU: FSC-88 acrylic primer from Coastal Enterprises and Dura Build automotive primer from Evercoat. With FSC-88, we thin and spray multiple coats, using a Wagner spray gun. It takes a while to cure, and we usually put a fan on it to speed things up. We spray Dura Build, with an HVLP sprayer. It’s lacquer-based and dries to sand or topcoat in minutes.

We don’t sand much before priming with FSC-88—we just knock down any trouble spots. The true sanding comes once primed. For a glass-smooth finish, we do a coat or two of FSC-88, sand thoroughly, then two coats of Dura Build, followed by a light sanding, and finish with Matthews polyurethane paint.

If we’re doing something that doesn’t require as perfect a finish (as when it’s going to be faux finished or distressed) we skip the FSC-88 and just use several quick coats of Evercoat before sanding and spraying with Matthews paint.

If it’s going to be finished with 1-Shot enamel, we usually use Evercoat primer. 1-Shot enamel is thicker and fills the surface well. This gives a fairly smooth finish.

The only exception to this process is when the sign has other materials on it besides HDU board. Then we a Matthews Epoxy Primer. It’s about the only thing that will prime wood if you’re going to topcoat with Matthews.

HDU quality and density also impact the process. We’ve discovered that higher density (20 to 30 pound) not only makes a more durable sign, but has a finer grain surface, which means it takes less effort to achieve a great surface. Lower-cost HDU is a false economy on many fronts. Duna Board HDU has been our go-to of late.

— John Ralph, Quail Run Signs, Hamilton, Virginia

We recommend priming Precision Board HDU with our FSC-88 WB primer, then following with the finish of your choice. This is a high solids primer, which means it will build up faster on the surface. Two coats are usually adequate, with no sanding between coats. This lets you build up more primer before the sanding starts. Any finish will adhere to this primer, and you can also use this product on any other substrate.

HDU is different than many other substrates. It doesn’t absorb moisture and is impervious to all solvents. FSC-88 WB will adhere to the surface of the HDU, which means you can build up the primer and sand to a very smooth finish if necessary. We have training videos on www.precisionboard.com that will help you get the best results when working with HDU board.

We also have texture finishes and doming resins that you can use on HDU. Everything doesn’t have to be flat and smooth, right?

— Kellie Miller, Coastal Enterprises Company, Orange, California

We first sand HDU with fine sandpaper, blow it off with compressed air, then prime with Sherwin–Williams exterior primer. We’ve applied the primer with both brush and spray, and find spraying gives a better finish. We finish with Sherwin–Williams water-based exterior paint and it works well.

— Ivan Rivero, Signs That Sell, Concord, California

We sand imperfections with 180-grit sandpaper then blow off any dust, chips or dirt with compressed air. We prime with Standox by Axalta Coating Systems, which is a polyester filler you spray on.

Using a spray gun with a 2.5 spray tip, we choke down the fan to about two inches wide and spray two fairly heavy coats of Standox in a crisscross pattern. Pay attention to the edges of the sign. Make sure you have good coverage so you don’t break through later while sanding.
Inspect the primer. Fill any pinholes by using the spray gun to rain a little Standox on them until they disappear. Standox takes a minimum of four hours to dry and will be sandable at that point.

Sanding the primer with 180-grit paper is fine for most applications. For a super smooth surface, sand down to 400-grit paper. The primer will be as smooth as glass. If you break through while sanding, spray a high build primer like Dura Build over the area and re-sand.
Now you can start the paint process. A paint sealer must be used before color is applied. After the sealer is dry, we finish using an automotive paint (base coat and clear coat).

— Corey Fisher, Metro Sign & Awning, Tewksbury, Massachusetts

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