Note: Concrete floors are treated separately, as they involve considerable expertise, specialized equipment
and materials quite different from general painting. This article is about general painting of interior and exterior
walls and ceilings.
Concrete of course is one of the most used building materials in construction, used extensively in commercial and industrial malls, high-rise buildings, office towers, underground parking garages, warehouses and factories. Because it is highly alkaline, steel embedded in concrete will not rust – a huge advantage for rapid construction of large buildings. Concrete can be poured in place, or manufactured off site and erected with tiltup panels like a large Meccano set. Concrete block can be used to create strong partition walls in a building, and many buildings are constructed with perimeter walls made of this material. Brick is more usually used in residential construction, but can also be used in commercial and industrial applications.
Concrete is obviously wet when it is poured, and takes some time (usually around 30 days) to fully cure and for the moisture level to drop sufficiently to accept paint. Doing moisture checks with a moisture meter is highly recommended to verify that the concrete or block is ready to paint.
While painting concrete is generally not too difficult, painting it without proper preparation or with the wrong product can lead to problems down the road. Chalkiness or form release oils on the surface will require pressure washing to remove. The high alkalinity often requires specialty primers to ensure long-term adhesion.
There is a wide variation on the products that can be used to paint concrete. One thing that is surprising to the uninitiated is the fact that concrete block walls can be painted with several coats and still not have an even appearance. The industry standard is to spray an industrial block filler and back-roll to fill the pinholes in the block; depending on the finish coat, our operators will often apply an extra coat by spray after back-rolling.
Elastomeric coatings are used when a waterproofing solution is needed on walls, or a particularly durable coating is required. As suggested by its name, elastomeric coatings form a very elastic and flexible film; for this reason, it is often used on older concrete to bridge hairline cracks that would otherwise involve expensive repair. The initial higher cost is more than offset by increased longevity, which is why it is often used to paint high-rise buildings where access forms a large portion of the budget.
Finally, another option for concrete and brick is to apply a concrete stain. These are intended to penetrate into the surface to change the colour and are sometimes a good choice.