Why Can’t Interior Paints be Used on The Exterior?

Interior paints can be used on external surfaces but this is not recommended by paint companies. This is because the chemical composition of interior paints is not formulated to sustain all the harsh weather changes and external elements like dust, fungus, pollution, smoke, heat, chill, rain etc. So with in a very short time, the paint might start deteriorating and sometimes might even show signs of breaking down, cracking and fading.

‘Alligatoring’ as depicted in the picture is a common problem that occurs when interior paint is applied on exterior walls. This is a patterned cracking of the wall paint where the cracks resemble the scales of alligator skin. Some reasons why it occurs are as follows:

  • Applying interior solvent-based enamel paint on exterior walls in an extremely hard and rigid coat or applying it on a more flexible coating like a water-based primer causes cracks to develop. Sometimes painting the walls of a balcony with a second coat before the base coat has dried properly also causes cracking.
  • But mostly natural aging of oil-based paints when seasonal temperatures fluctuate is also a reason for paint deterioration on exterior walls. This type of steady expansion and contraction causes loss of paint film elasticity. Moreover interior paint is even more susceptible to break because it cannot resist the harsh weather conditions outside.

As a result of these problems, paint companies advise customers not to apply interior paint on exterior walls. They manufacture top quality paint solutions especially formulated for external walls and these are ideal for usage on walls on the outer side of the house.

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