PAINTING POLYSTYRENE FOAM

Q. I am the manager of a manufacturing facility that is old but in good condition. We are in the process of painting and freshening up the facility for an open house, and are wondering what sort of paint is required to refinish the insulating panels on the roof of our building. These panels, which are actually the plant ceiling, are made of thick polystyrene foam and are a blue color. The building is old and we presume the roof panels are, too. They are in good condition but unsightly and we’ve concluded that if we can paint the polystyrene foam it will really brighten up the plant. We are also aware that by painting them we may risk destroying them due to the nature of the material. What can you suggest as a solution to our problem? D.A.

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A. In 1963, when waterborne industrial finishes were being introduced, I was asked a similar question. One of my company’s divisions wanted to insulate compressed air tanks for outdoor equipment using expanded polystyrene beads, a material similar to your roof panel insulation. They wanted to paint the insulation with a paint finish matching the equipment. They found that paints containing solvents attacked and dissolved the polystyrene foam. Owing to my experimental work with waterborne coatings, I was able to recommend a water-soluble primer for use over the polystyrene. After priming to protect it, the insulation was coated using the standard outdoor finish system for that equipment. Now, 45 years later, waterborne paints are practically the industry standard.

You can paint polystyrene foam or expanded polystyrene beads using a waterborne paint to protect it from solvent attack by subsequent coats of paint.

Typical waterborne paints are acrylic or vinyl lattices used for painting building interiors and exteriors or water-soluble industrial paints. After the polystyrene is completely covered, you can over-coat it using a conventional paint, if need be. In your case, you should consider using a white waterborne ceiling paint because of its high reflectivity.