Paint coatings with visible cracks which may penetrate down to the substrate. Cracking comes in several forms, fro minute cracking to severe cracking.

Mud cracking is a coating flaw that occurs on the surface of a wall that looks similar to deep and irregular mud cracks on the surface of the earth. This phenomenon occurs when an over coating is applied on curved surfaces and unprepared surfaces. It is common along corners where there might be an accumulation of paint.

On metallic substrates, this can also be an indication of a growing corrosion or stain which was not properly rectified during sanding and scraping off of irregularities.

Figure 1. Mud Cracking

Figure 2. Cracking

• CAUSES:• Generally over application of heavily pigmented primers such as inorganic zinc silicates or water based coatings, although can occur with other over thick systems.
  • Paint applied too thickly, usually over a porous surface.
  • Paint applied too thickly, to improve inherent poor hiding (coverage) of a lower quality paint.
  • Paint is allowed to build up in corners upon application.

  PREVENTION:

  • Only apply the recommended coating thickness.
  • Use recommended application techniques with suitably formulated products.
  • Paint applied too thickly, usually over a porous surface.
  • Paint applied too thickly, to improve inherent poor hiding (coverage) of a lower quality paint.
  • Paint is allowed to build up in corners upon application.

  SOLUTIONS:

  • Remove coating by scraping and sanding.
  • Prime and repaint, using a top quality latex paint.
  • Mud-cracked areas can also be repaired by sanding the surface smooth before repainting with a top quality latex paint.
  • This type of paint is likely to prevent recurrence of mud cracking, because it is relatively more flexible than alkyd paint, oil-based paint and ordinary latex paint.
  • Quality paints have a higher solids content, which reduces the tendency to mud crack.
  • They also have very good application and hiding properties, which minimize the tendency to apply too thick a coat of paint.

  REFERENCES:

  1. The MPI Group, Coating Defects, data of access: 15 July 2016, http://www.mpigroup.co.uk/publishing/fitzs-atlas-of-coating-defects/translation/4-coating-defects/
  2. Paint Quality, Identifying and Resolving Common Paint Problems, data of access: 15 July 2016, http://www.paintquality.com/en/tools/problem-solver