Guidelines for Substrate Preparation
How to prepare a surface for Italian Decorative Finishes
Venetian plaster substrate preparation is one of the most misunderstood topics and also, one of the most important factors that you should not overlook when doing high-end Italian decor. You -whether you’re an applicator or a specifier- should be aware that none of the decorative finishes (microcement, resins, paints and polished or Venetian plasters) should be used for decoration if the substrate hasn’t been prepared properly to ensure a durable and beautiful look.
First and foremost you have to ensure that the substrate is smooth and firm enough. If movement is expected or seen then you need to address it without delay as Venetian plaster is not structural, but a decorative coating. Italian decorative finishes won’t hold the substrate together; the finish will not keep the wall whole and intact when the base cracks.
Reasons for the cracking
Why cracks appear on Venetian plasters, polished plasters and Italian Paints
Cracks can appear because of a number of reasons. The most common reason is mechanical impact – building or decorating work can affect the integrity of the surface, the house can settle, the joints and boards might expand. On the other hand, it can also be thermal, when the substrate is affected by direct heat or must endure significant thermal amplitudes (e.g. due to (underfloor) heating turned on and off, being in the kitchen, applied on metal, etc).
Most of our lime, acrylic and microcement plasters are formulated to endure even direct heat, please contact us with your requirements for further information!
The use of anti-crack systems
or how to ensure the look of microcement, Venetian or polished plasters and other Italian decorative finishes with the correct substrate preparation application
Independent of the reasons, it is highly advisable that you apply on top of any Venetian plaster, Italian paint or microcement an anti-crack system. The anti-crack system currently offered for Venetian plasters by Impera Italia is Colbeton, a resinous plaster in powder form, that should be applied on two coats, with a mesh embedded in the first coat. You should also use a 160g/sqm mesh with good tactile strength like ours.
Once the anti-crack coating is done and is completely dry, you will need to ‘bridge’ the heavy grain of the anti-crack coating with a suitable larger grain Venetian plaster. Why is this so important? Because if polished plasters or paints are specified as the final finish the grit of the anti-crack system would show through. For a seamless look apply a fine Marmorino plaster-like our Marmorino Fino or Classico; this also helps to regulate the consumption of the final finish. Generally speaking, a single coat of the ‘bridging plaster’ applied will be fine; it can be used uncoloured, in white as it doesn’t show through when covered with the decorative finish.
Once all the above is done and you applied the finishing plaster or the paint, our anti-crack solution will give the wall the necessary solidity to endure most small to medium cracks.
If you are 100% sure that the substrate is firm and smooth enough to take the finishing coating then the plaster or paint can be applied directly on top of an appropriate primer like our Unifix, Marcotherm or Universal Primer. The anti-crack coating, if you apply it correctly, is a purely structural part and does not affect the look.
Substrate preparation specifying notes for applicators
Impera Italia always recommends that -unless the surface section has been specified and checked by the person applying it from the ground up and it is very flexible- you should always consider using an anti-crack coating before applying an Italian finish. This not only raises confidence that the finish will last but also helps you to get the look right!
If you have any further questions, please don’t hesitate to get in touch.
Copyright 2019 by Impera Italia. Can not be distributed, used or changed without the written consent of Impera Italia