One of the most dramatic causes of wall painting degradation is the slow transformation of the calcium carbonate binder, CaCO₃ into selenite, CaSO₄.2H₂O, due to the combined action of polluting SO₂ and oxygen. This process is called sulphatisation and the effects on the paintings are loss of colour transparency and loss of cohesion of the painted layers. The present paper reviews the sulphatisation process and the peculiarities of both the Ferroni-Dini method and Ca(OH)₂ nanotechnology for pre-consolidation, cleaning and consolidation of wall paintings affected by sulphatisation. We show that the mechanical stress induced by the volume expansion associated with the transformation calcite ⇒ selenite plays a critical role in wall painting degradation by sulphatisation. The first step of the Ferroni-Dini method, consisting of treatment with ammonium carbonate by means of wood poultice compresses, is shown to be effective in removing selenite and converting it into ammonium sulfate. Furthermore, the consolidation induced by the second step of the Ferroni-Dini method, consisting of barium hydroxide treatment, is shown to be due to two different mechanisms: the ‘voids filling’ by BaSO₄ and BaCO₃ crystal formation and the generation in situ of ‘fresh’ lime responsible for a new setting process. The innovative pre-consolidation treatment by Ca(OH)₂ nanoparticles is shown by examples from real cases in important conservation workshops. Applications of the Ferroni-Dini method and Ca(OH)₂ nanotechnology in other fields of work of art conservation are briefly discussed.