The problem of mottled color is caused by white salt stains (Efflorescence).

Generally, this occurs on the surfaces of concrete, brick, or natural stone where salts can penetrate the surface, with moisture acting as a catalyst, resulting in white stains on walls or cracks that resemble discoloration or fading. If severe, it can be seen as clearly defined white salt efflorescence, especially on dark or bright-colored walls.

Causes

• Painting over plaster walls that still have high moisture and are not dry enough.
• Painting over while the primer is not completely dry.
• Incomplete curing of the plaster, leading to efflorescence and high moisture.
• Water seeps into the walls through cracks, dissolving the salts in the plaster, and when the water evaporates, small salt crystals form along the cracks in the plaster.
• Using the wrong type of primer, such as using old plaster primer on new plaster walls.
• Using low-quality primer or topcoat that may have poor resistance to salt efflorescence.

See other solutions for rainy season home problems.

Correction Guidelines

• Wash the salt stains off with clean water and leave to dry completely for at least 1-2 days. If the problem is not severe, the salt stains will disappear. However, this method is only a temporary solution that may return if the walls remain damp or cracked. Therefore, to stop the problem, it is recommended to repair the walls and repaint them correctly.
• In case of cracks, fill the cracks with appropriate filler material based on the size of the cracks, such as Beger Acrylic Filler F-200 for cracks no larger than 1 mm, or Beger Acrylic Sealant F-001 for cracks no larger than 2 – 10 mm, using tools like a metal trowel or Beger PU Seal with a caulking gun, and then smooth with sandpaper.
• Once cleaned and filled, apply a suitable plaster primer for the type of plaster surface. It is recommended to use the multipurpose primer Beger Super Quick Primer B-2100 or Beger Rain Quick Primer B-2900 (water-based) in one coat, and let it dry for at least 4 – 6 hours.
• Apply a high-grade topcoat such as BegerCool Diamond Shield 15 or interior paint BegerShield AirFresh Anti-Virus Gold Ion in two coats.