Oct 2020 Plastering Defects and Their Causes
Creating a lush velvety visual appeal, when applied using the correct plaster mix ratios, excellent quality cement, and routine maintenance, Sephaku Cement explores plastering defects, their causes, and how these can be prevented.
Offering a world of choice by way of paint colour and texture finishes, the use of stencils, wallpaper and vinyl applications, plastered walls create the ideal canvas for diverse interior decor and beautifying details. But much as the same as sound concrete foundations determine the stable and steadfast footing of a structure, sound plastering is the difference between a lasting concrete finish versus plastered surfaces blemished by unsightly damage and plastering defects.
To follow Sephaku Cement reveals the various plastering defects, what causes plastered cement blemishes, and how these can be avoided.
Blistered Plaster Finished
Resembling sunburnt skin covered in bulging watery blisters, while blistered plastered finished are not filled with water, this plaster defect can be caused by an uneven plaster mix that results in late slacking on account of lime and water in the plaster.
To prevent this cement plaster defect, when mixing up a batch of plaster, be certain to pay very close attention to the plaster mix and cement/aggregate ratios.
De-bonding of a plastered surface
One can spot a de-bonded plaster finish by its cracked and fissured surface and the hollow sound the plaster makes when gently tapped. Appearing to lift or peel away from the wall, this plastering defect occurs when the plaster is too thick. As the surface of the plaster, if exposed to the elements, the skin of the plaster tends to shrink at a different rate to the thick layer of plaster or substrate beneath. To prevent the de-bonding of plastered walls, be certain to adequately prepare the substrate, cleaning away any dust, debris, and any oil that will inhibit a secure bond between the substrate and plaster. And much as one would hydrate any other concrete application during the curing process, ensure that the plastered surface is able to reach suitable tensile strength before losing enough moisture to induce cracking. Alternatively do plaster work when the roof has been installed or when it is cooler in other words start plastering a bit later in the day so as to prevent too much sun/heat on the plastered surface. The other way is to use curing compounds and or wetting after strength has been obtained. Most plaster defects occur with sudden drying out of the plaster after placing and finished. (minimise evaporation of moisture to the minimum)
Efflorescence on Plaster
As concrete /plaster cures bringing the salts present in the cement aggregate and water blend (and often even the bricks themselves) to the surface of the concrete /plaster application, a white chalky crystalline substance can appear on the surface of a plastered wall. Referred to by cement /concrete professionals as efflorescence or in builders terms are also called “Lime-Bloom”, this plastering defect not only creates an unsightly appearance on the surface of plaster but can adversely affect the adhesion of paint, wallpaper, and vinyl decals applied to the wall. Prevent this unsightly chalk-like ooze from newly plastered walls but making sure to use a good quality cement product and water free from salt while also ensuring the internal surface or substrate is adequately damp sealed.
While these are just a handful of defects that can occur on plastered walls, and each of these are relatively easy to repair, when any of the above plastering defects takes place, which can be significant enough to have to replace an entire plastering job which can be expansive and equally expensive.