Exterior Painting and Primer Guide

Polyurethane facade elements leave the factory with a white industrial acrylic primer. That primer is a technical base prepared for paint adhesion; it is not a finish coat. Outdoors, without a topcoat the surface yellows and fades under UV. The sequence below is designed to protect both the life of the paint and the paint manufacturer’s warranty.

• 180-220 grit abrasive paper • Acrylic or exterior filler • System primer of the topcoat brand • Elastic, UV-resistant facade paint • Brush/roller or gravity-feed spray gun • Damp cloth for cleaning

1) Surface cleaning and matting The whole surface is lightly matted with 180-220 grit and dusted off. Because a silicone-based release agent is used in production, residue may remain on the surface; if it is not removed the paint will peel. 2) Filling joints and screw heads Screw heads, joints and level differences are filled flush with acrylic/exterior filler. Once dry, the marks are removed again with 180-220 grit. 3) Homogeneous primer coat Primer is applied homogeneously to the WHOLE surface, not spot-applied. Priming only the filled areas creates absorption differences and leaves tonal or gloss variation in the topcoat. 4) The system-primer rule The intermediate primer must be the system primer of the same brand as the topcoat. Paint manufacturers decline responsibility for blistering and peeling — even when the fault lies in their own product — if their system primer was not used. 5) Elastic topcoat Outdoors a highly elastic, UV-resistant facade paint is applied (for example the premium exterior ranges of Jotun or Filli Boya). Two coats is the interior standard; outdoors follow the coat count and waiting times specified by the manufacturer.

The factory primer is a white industrial 1K acrylic layer whose purpose is to improve paint adhesion. It provides no UV protection. A product left unpainted outdoors yellows over time; this is not a material defect but the result of an incomplete application.

Water-based, synthetic and cellulosic solvent paints can all be used on polyurethane surfaces. Outdoors the decisive criteria are elasticity and UV resistance: elastic systems reduce the risk of hairline cracks and a UV-resistant topcoat prevents yellowing. Metallic (gold/silver/pearl) paints are solvent-based and are sprayed with a gravity-feed gun using a nozzle of at most 1.3 mm.

There are three typical issues. Peeling usually comes from release-agent residue or skipped primer. Blistering is mostly caused by water or moisture ingress from behind pushing the paint off; polyurethane itself is unaffected by moisture, and paint should not be renewed before the source is fixed. Tonal variation signals absorption differences left by spot priming.

The product itself needs no maintenance: there is no rot, no insects and no periodic varnishing. Maintenance depends entirely on the life of the topcoat and follows the interval set by the paint manufacturer. Impact damage is repaired with acrylic filler, sanding and touch-up.

Not outdoors. The factory primer provides no UV protection; an unpainted surface yellows and fades over time.

Primer is mandatory. It improves adhesion, and for warranty purposes it must be the system primer of the topcoat brand.

This range mattes the surface without scratching it and improves mechanical adhesion. Coarser paper leaves marks, while finer paper does not remove release-agent residue sufficiently.

Two coats is the interior standard. Outdoors, the number of coats and the waiting time between them follow the technical data sheet of the chosen paint system.