Dealing with crazy-cracking

Under certain conditions, new cement plaster hardens with a hexagonal pattern of very fine cracks present, roughly the size of an adult's hand. These are not visible to the eye, but if a solvent based bonding liquid is applied to the surface, their presence is shown very distinctly. As things stand there is no special coating requirement, and the usual one coat of a Masonry Primer and two coats of a good top-coat will suffice. A big problem, however, arises when these cracks open and close under large temperature changes or settlement of the new structure.
The very standard coating procedure given above will provide up to 100 microns of top-coat. When these cracks open - often as much as 500 microns, huge stress is applied to the dry paint film above the crack. Upon stretching to accommodate the crack below, the paint film above it becomes thinner, much like a rubber band would if stretched. For a paint film to accommodate that type of stress, not only does it need to have an intrinsic degree of flexibility, but there also needs to be enough film thickness to allow that type of elongation without the film breaking above the crack.
The leading  international Pure Acrylic binder manufacturer conducted a series of tests to determine the film thickness required to successfully bridge opening cracks of this nature. Not surprisingly, the binder had to be of a highly flexible nature - but what was surprising was the fact that a minimum film thickness of 320 microns was required to survive the ordeal. This would require around 7 coats of most top-of-the-range pure acrylic exterior coatings currently used in the South African paint market. I have never seen a specification calling for 1 coat Masonry Primer and 7 coats pure acrylic top-coat before!
Should you need to re-coat a wall where crazy cracking is evident, after surface preparation, apply one coat Plaster Primer, followed by two coats Elastocryl ( a fibre re-enforced, high solids, pure acrylic coating) at 5 square metres per litre before coating with two coats of the chosen top-coat. Better still, contact us for advice specific to your job's requirements.