What is the best way to prime and paint Eucaboard?

We wanted to paint slick white pvc piping in the laundry room.

This specific Valspar primer was suggested for our slick plastic pvc surface and it preformed marvelously.

Perhaps it might work for you, sorry not familiar with Eucaboard personally. Valspar help line might be a good place for a consultation.

Eucaboard is basically hardboard panels with one side finished with a bonded glossy membrane. You would need to lightly sand the surface to roughen the surface for paint. Sanding also removes the glossiness of the surface. Wipe off all the sanding dust with a damp cloth. Then prime with Kilz primer and paint. I hope you used thicker panels of Eucaboard over the studs with insulation and a vapor barrier within the walls. A lot of building codes require hardboard panels placed over drywall.

If I were you, I'd find an inconspicuous spot or maybe you have a piece of the board and test it first. Chalk paint can be very expensive but there are recipes online to make your own much cheaper. I'd test it with chalk paint because it really does cover most things even glass without having to sand and prime first. That would save you so much work and time, if it works! Hope this helps and good luck!

Also called Masonite or hardboard I had a hard time finding an answer for you because there are many different approaches to this. I think this link relates to you question best

The one thing that this link doesn't address is the type of primer most every other suggests using an oil-based primer not latex because Water based products tend to raise the the grain or fester up the manmade panels or boards. But after the oil based primer it is suggested you can use latex paint.

Hope this helps with your project.