Why is it important to understand how Crackle Products work?


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Revision as of 06:47, 22 July 2011

 Image:Old door in Bergamo Italy.JPG

Crackle products have long been used to replicate the failure of paint and plasters as they weather and age.

This is a critical consideration, as the coatings formulator is faced with the task of developing a product that “fails” in a very specific and controllable manner, but still provides a robust and durable surface. What this means for the decorative painter is that cracking products require more attention to detail as they are not as inherently foolproof as other decorative paints and textures.

In the case of crackles, the product must be designed such that it does not completely coalesce as the water and solvents evaporate from the wet film, so that it will fracture (crack) as the film shrinks as it dries. But we also want the crackle to adhere tightly to the substrate as it fractures. As a result, as the curing film shrinks and cracks, it puts a lot of stress on the layers of paint and other products underneath it. If there is a layer with weak adhesion, as the cracking texture moves and cracks as it dries, it can cause that layer to separate from what is beneath it and there will be a loss of adhesion. Crackle Surface Preparation and Protection advises on the issues that painters need to be aware of as they design finishes that incorporate these products.

The following series of images illustrate what is happening physically to layers of paint and primer beneath the Crackle application. The material with the greatest strength will draw the weaker in whatever direction it wants to go in as it dries. This is why the strength of a painted layer can surpass the strength of the substrate. The greatest bonding strength will win over the weaker.

(Image here) Step 1. We loosely taped a piece of saran wrap to a piece of cardboard. The Saran Wrap represents a coat of primer applied to a wall (the cardboard). Any dust that lies between the layer of paint and a wall or paint and plaster will act like rollers and create glide, not allowing 100% adhesion to develop between primer and the wall. Of course, this defect remains undetectable to the naked eye.

(Image here) Step 2. We rolled on a layer of house paint(representing the Crackle application) to the saran wrap (representing the primer). Paint contracts as it dries and creates air pockets and cracks.

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