A method to strengthen the anchorage of a plaster layer to a plaster-holding structure; said plaster layer having a first surface arranged facing, and immediately close to a first surface, of said plaster-holding structure, said method being characterized in that it comprises the following steps: providing a plurality of springs (3, 5), each of which is constituted by a first tubular portion (3a, 5a) and a second portion (3b, 5b) which extends projecting from said first tubular portion (3a, 5a) along a longitudinal axis; forming at least on said first surface of the plaster layer a plurality of holes which extend along respective approximately parallel and spaced apart from one another axes; fitting the second portions (3b, 5b) of the springs (3, 5) in respective said holes so as to arrange the respective first portions (3a, 5a) resting on a second surface opposite the first surface of the support structure; making the second portions (3b, 5b) of the springs integral with the inner walls of the corresponding holes in the plaster layer by way of fastening means provided in the holes themselves; wherein some of said springs (3, 5) are anchoring springs for the plaster layer and are each constituted by an approximately mushroom-shaped wire helical spring wherein the first portion and the second portion have a cylindrical or conical shape and form the head and the stem of the spring respectively; wherein said fastening means comprise a fastening mixture made of adhesive material and/or resin; said method comprising the step of injecting a predetermined quantity of said fastening mixture into said hole so as to rigidly fix only an end portion of said second portion (3b, 5b) of the springs (3, 5) to the inner wall of said hole in the plaster layer. providing a plurality of springs (3, 5), each of which is constituted by a first tubular portion (3a, 5a) and a second portion (3b, 5b) which extends projecting from said first tubular portion (3a, 5a) along a longitudinal axis; forming at least on said first surface of the plaster layer a plurality of holes which extend along respective approximately parallel and spaced apart from one another axes; fitting the second portions (3b, 5b) of the springs (3, 5) in respective said holes so as to arrange the respective first portions (3a, 5a) resting on a second surface opposite the first surface of the support structure; making the second portions (3b, 5b) of the springs integral with the inner walls of the corresponding holes in the plaster layer by way of fastening means provided in the holes themselves; wherein some of said springs (3, 5) are anchoring springs for the plaster layer and are each constituted by an approximately mushroom-shaped wire helical spring wherein the first portion and the second portion have a cylindrical or conical shape and form the head and the stem of the spring respectively; wherein said fastening means comprise a fastening mixture made of adhesive material and/or resin; said method comprising the step of injecting a predetermined quantity of said fastening mixture into said hole so as to rigidly fix only an end portion of said second portion (3b, 5b) of the springs (3, 5) to the inner wall of said hole in the plaster layer.