Why does the paint film not cover the underlying surface/old paint work

Substrate showing through the top-coat. Old paintwork, spot primer are visible through the top-coat

What are the possible causes?

• Paint diluted beyond the recommendation.
• Base coat darker shade than top coat.
• Painting on absorbent substrate also shows poo hiding.
• Paint may not stir uniformly before application.

How can I fix the problem?

• Stir sample thoroughly before application
• Apply primer coat followed by top coat, if the base colour is darker.
• Use thinner recommended by paint supplier.(Don’t over dilute it)
• Apply recommended film thickness with correct tools.