Coating failures can occur from a number of reasons, largely grouped into the following categories :

 

  1. Improper selection of coatings – for example, a coating suitable for exterior steel structures may be inappropriate for the interiors of a water tank.
  2. Extreme exterior forces – chemical exposure, abrasion or weathering.
  3. Material incompatibility – the coating may undergo chemical reactions with the substrate
  4. Inadequate adhesion – the density and smoothness of the surface may cause the coating to have poor adhesion.
  5. Poor or inadequate surface preparation – surface contamination or poor surface profile.
  6. Poor or inadequate application – inadequate thickness control, pinholes, overspray, or improper drying.
  7. The design of the structure itself – Sharp edges, crevices, skip welds, back to back angles are focal points for failure.

 

Below is a guide for some of the more common symptoms :

Efflorescense

 

Formation of white powdery surface deposits, usually on exterior walls.

  •  Migration of alkaline from cement, crystallized on the surface as salts
  • Use of paint on insufficiently dried cement/concrete (with moisture content > 6%)
  • Excessively pigmented or aged paint films releasing its paint pigments as the binder begins to break down
  • Efflorescence can be washed away using water jets
  • Ensure that the moisture content of the surface does not exceed 6% (or refer to manufacturer’s recommendation) prior to recoating
  • Seal off with a compatible alkali resisting primer before painting
  • Use epoxy based paint for persistent, severe cases

Excessive Brush / Roller Marks

 

The paint has failed to dry to a smooth, uniform finish.

  • Use of low quality paint. The paint has too much thickener and poor self-leveling properties
  • The paint dries too quickly and form streaks before it can level out properly
  • Build up of paint due to repeated re-brushing or re-rolling of partially dried painted areas, often for “touch-up” purposes
  • Use of wrong type of paint roller (the nap is too long for the paint type or surface), or poor quality paint brush
  • Use high quality paints and applicators which are appropriate for the surface and work
  • Always maintain a “wet edge”  – do not allow the edge of freshly applied paint to stand and dry out. Apply paint toward unpainted areas and then back into the just painted section. Rolling back and forth between “wet” and “dry” areas will produce a smooth uniform finish

Blistering

 

A portion of the paint film experiences loss of adhesion and becomes partially detached from the substrate, causing a raised “bubble” or “blister”

  • In most cases these blisters are caused by water vapour in the substrate, being “attracted” to the surface via temperature differential, and then being “trapped” behind the impervious paint film
  • Use of paint on insufficiently dried cement/concrete (with moisture content > 6%)
  • Use of paint on a hot surface
  • Exposure of paint film to dew, mist, high humidity or rain, before it has dried
  • Remove defective paint and prepare surface accordingly to receive paint
  • Ensure that the moisture content of the surface does not exceed 6% (or refer to manufacturer’s recommendation) prior to recoating

Peeling

 

Loss of adhesion to the substrate.  There are 3 major possible causes.

– Moisture issues

  • For peeling on ceilings – water seepage through roof, toilets etc
  • Use of paint on insufficiently dried cement/concrete (with moisture content > 6%)

 

– Incorrect paint system

  • Failure to use appropriate sealer / primer
  • Failure to use etching primer for ferrous metals
  • Use of poor alkali resisting primer/undercoats or insufficient penetrative primer

 

– Improper surface preparation

  • Failure to remove unstable matter during surface preparation

 

– Moisture issues

  • Install proper waterproofing system before painting
  • Arrest moisture source
  • Ensure that the moisture content of the surface does not exceed 6% (or refer to manufacturer’s recommendation) prior to recoating

 

– Incorrect paint system

  • Prime/seal all bare surfaces with appropriate primer or sealer

 

– Improper surface preparation

  • Remove all defective and loose paint film, and unstable matter such as plaster etc
  • Prime/seal the surface with appropriate primer/sealer to further stabilize the surface
  • Re-coat with appropriate coating system

 

Lifting

 

Heavy wrinkling caused by attacking of successive coating on the existing paint

  • Use of incompatible coatings
  • The top coat utilizes a thinner that is much stronger and reactive than the undercoat, and as it dries, the paint film shrinks and lifts the entire undercoat off the substrate, which results in the wrinkling effect
  • Allow undercoating to dry before application of successive coating. Observe overcoating intervals as recommended by manufacturer
  • Sand and clean receiving surface before application
  • Overcoat with appropriate coating as recommended by manufacturer

Fading

 

Loss of vibrancy of colors due to exposure to sunlight

  • Use of vibrant coloured paints made with organic particles that are easily susceptible to UV degradation, e.g. bright yellow, orange, red or blue
  • Use of paint with water sensitive pigments
  • Use of paint with low quality emulsion paints
  • Paint fading cannot be eliminated and can only be reduced. Paint colour fades on an estimated rate of 20% year on year under normal wear and tear. This means that after 5 years, only about 41% of the original colour will remain. As such, color differences experienced during re-coating or touch up of the finish after some time is normal
  • Use paints with better opacity, UV stability and colour-fast properties. These include paint colors made with natural oxide pigments, such as black oxide, yellow oxide, red oxide, brown iron oxide and chrome oxide green