Guidelines for Substrate Preparation for Italian Decorative Finishes
Venetian plaster substrate preparation is one of the most misunderstood topics and also, one of the most important overlooked factors when doing high-end Italian decor. Applicators and specifiers 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 it needs to be addressed without delay as Venetian plaster is not a structural, but a decorative coating. It won’t hold the substrate together; the finish will not keep the wall whole and intact when the base cracks.
Reasons for cracks on Venetian plasters, polished plasters and Paint
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 in direct contact with heat or must endure significant heat amplitudes (e.g. due to (underfloor) heating, 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 to ensure the look of microcement, Venetian or polished plasters and other Italian decorative finishes
Independent of the reasons, it is highly advisable that any Venetian plaster, Italian paint or microcement is applied on 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. It’s also advisable to use a 160g/sqm mesh with good tactile strength (please find further details on our website here).
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’ suffices and 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 the finishing plaster or the paint was applied our anti-crack solution will give the wall the necessary solidity to endure most small to medium cracks.
As a final note it needs to be mentioned that naturally, if 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 Unviersal primer. The anti-crack coating is not needed and ideally, should not affect the look, it is a purely structural part.
Substrate specifying notes for applicators
Impera Italia always recommends that -unless the surface section has been specified and checked by the contractor from the ground up but- clients should always be offered the option of an anti-crack coating. This not only raises confidence, makes the specifier aware or possible difficulties, but also gives them the option to control and balance the budget with the look and durability directly.
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