An overview of salt decay problems in plasters and renders is given on the basis of five historic buildings in Portugal. The diagnosis methodology, based on site-inspections and on a defined sampling/testing procedure, is presented and discussed. The use of high alkali content mortars and cracking of plasters/renders are recurrent causes of decay. Rising damp and condensations were found to be the most frequent origins of the moisture. Repair strategies for the five cases are indicated.