Where the Existing Coating is Unsound
All of the loose, unstable coating must be removed before repainting. Sand the areas of old, unstable paint with 80 to 120 grit or 180 to 240 grit abrasive paper to remove all loose and unstable areas and to refresh the surface. Where the unsound coating meets sound existing paint, feather the edges of the sound paint with 180 to 240 grit paper, then lightly sand the surface of the sound paint to enable the new coating to key to it. Where needed, apply a filler to smooth out holes and imperfections in the surface. Scrub down sound existing paint with an oil-free detergent such as Sugar Soap (normal dishwashing liquid is not good for this), to remove any stains or dirt. The surface should be wiped down with a damp cloth to remove any remaining dust and cleaning residue. Re-apply the entire prepcoat and topcoat paint system, as specified for the substrate.
Note: Where the substrate is metallic, if rust is present, all rust should be removed by grinding or sanding, and the area should be primed with a cold-galvanising product or similar zinc-rich primer.
Where the Existing Coating is Sound (and Acrylic)
The existing acrylic coating should be scrubbed down with an oil-free detergent such as Sugar Soap (normal dishwashing liquid is not good for this), to remove any stains or dirt. Once cleaned, the surface can be lightly sanded with 180 to 240 grit paper, and wiped down with a damp cloth to remove any remaining dust and cleaning residue. Apply a quality acrylic topcoat as specified for the substrate. An oil-based topcoat should not be applied over an existing acrylic topcoat as this can lead to cracking.
Where the Existing Coating is Sound (and Oil-Based)
The existing oil-based coating should be scrubbed down with an oil-free detergent such as Sugar Soap (normal dishwashing liquid is not good for this), to remove any chalking, stains or dirt. Once cleaned, the surface can be lightly sanded with 180 to 240 grit paper, and wiped down with a damp cloth to remove any remaining residue. A quality acrylic or oil-based prepcoat should be applied to the surface, followed by a quality acrylic topcoat, as specified for the substrate.
Where the Existing Coating is Sound (and Stained / Clearcoated Timber)
If the exterior cladding is a stained or clear-coated timber, the entire area should be sanded with 80 to 120 grit or 180 to 240 grit abrasive paper to create a roughened surface to promote adhesion of the new coating. The surface should be wiped down with a damp cloth to remove any remaining dust. A high-adhesion, acrylic or oil-based prepcoat should be used, followed by a quality acrylic topcoat as specified for the substrate.
Tip: After sanding and existing exterior coating, it’s a good idea to apply the prepcoat the same day, as night time dew can creep under the freshly sanded paintwork, causing the edges to curl and lift.