CRACKING OR RIPPLING

Description of problem:  6-_cracking_or_ripling.jpg
    Cracks show in one of the ground coats.
Causes:         
    – Difference in solubility between paint films due to the aging and hardening of the surface.                                       
    – A ground coat which has been force-dried at elevated temperatures before polishing and     
      application of the final coat.
    – Sandwiching a synthetic product such as synthetic primers between 2 coats of
      nitro-cellulose  paint.
    – Excessive delay before applying the second coat of a synthetic paint
      (the 1st coat has begun to dry).
    – Using an “incorrect” isolating primer instead of removing the old paint.
    – Strong solvents in the top coat attacking a synthetic primer that has been applied very
      thick with minimal or no flash off times between coats.
Note:
    – The application of thick wet coats of synthetic paint increases the chances of cracking.
    – The difference in flexibility between 2 types of finishes whereby the 1st coat is more
      flexible than the 2nd one usually leads to cracking.
Preventive measures:
    – Sand the original paint very well before painting (in some cases isolate or remove old paint).
    – Make sure that the temperature of the surface to be painted is the same as the
      ambient temperature.
    – Avoid thick coats.
    – Never sandwich a synthetic product between 2 NC coats.
    – Perform solvent test.
    – Ensure sufficient drying.
Note:
      It is wise to make a test on a small surface before painting. If cracking occurs, it is best to 
      apply GenPox isolating primer over the entire surface.
Remedy:
    – In extreme cases, sand all the way through to the bare metal, clean with Valox and respray.
    – In minor cases, especially with T.P.A (Thermoplastic Acrylics) you may sand with
       P1200 and polish.