Why Painting Brick is a Bad Idea

 

Why Painting Brick is a Bad Idea

By Frederick M. Hueston, Stone Forensics

 

That ugly, deteriorating brick wall needs to be cleaned and painted. So out comes the pressure washer to clean it and then an application of several coats of paint. BAD IDEA.  Painting brick can cause all kinds of problems and if that brick is already deteriorating than painting it will only accelerate the damage. The following article will explain why painting brick is a bad idea.

 

Types of Brick

Before we understand why paints, coating, sealers etc are a bad idea for brick we must first understand what types of bricks are out there as well as how brick react to moisture.

In the construction industry there are basically five brick types

 

• Burnt clay bricks

These are the most common bricks and the ones normally found in most homes and buildings. They are made from wet clays, compressed and fired in a kiln. They are commonly red in color but can be found in almost any earth tone.

• Sand lime bricks (calcium silicate bricks)

These are manufactured by a combination of sand, fly ash and lime. Color pigments are added for various colors. Unlike burnt clay bricks they are not fired with the same technique. They are molded under heat and pressure and form a chemical bond to hold them together. The are usually gray in color but can be any color. Their finish is smoother than other brick types and are often used for strength.

• Concrete bricks

Concrete brick as made of Portland cement mixtures. They are also available in various colors. They are commonly used in fencing and interior brick work

• Fly ash clay bricks.

These are light weight bricks since they contain fly ash. They tend to expand in in the presents of moisture. They are also highly fire resistant and often used foundations

 

 

 

• Refractory Bricks

These types of bricks contain special blends of earth and aluminum oxide. They can withstand extremely high temperature. They are commonly used inside chimneys and furnaces as well as pizza ovens and outdoor barbecues.

 

Brick Properties and its Deterioration

More than likely the brick you plan on painting is very porous. Of course, the mortar between the brick, which is called “point”, is also very porous. Most paints, sealers and other coating and treatments are not breathable or what is called vapor permeable. This prevents water from escaping the brick and mortar.

Most of the problems associated with brick can be traced to moisture or water intrusion of some kind. Many stains are caused by the presents of water. Water is an essential ingredient for the setting, cleaning and restoration of brick, but it can also be its number one enemy.

What problems are associated with moisture and water.  The following is a brief description of these problems.

Efflorescence

Efflorescence appears as a white powdery residue on the surface of the brick.  It is a common condition on new brick installations or when the brick is exposed to a large quantity of water, such as weather and washing.  This powder is a mineral salt from the setting bed or brick itself.  To remove efflorescence do not use water, brush the brick with a clean soft nylon brush.  The brick will continue to effloresce until it is completely dry.  This drying process can take several days to as long as one year or more.

Subflorescene

Subflorescene is what happens when the mineral salts migrate and do not make it all the way to the surface. In the efflorescence condition above, the salts are deposited on the surface of the brick. In subflorescene the salts crystallize just below the surface, causing stress within the pores of the brick. The result is a condition known as spalling which appears as pits or flaking in the surface of the brick.  subflorescence is very common on brick and is very common on almost all masonry surfaces where de-icing salts are used.

 

 

Mineral crusts or Lime Putty

 

Mineral crusts or lime putty can be recognized by its white crust like formation on brick surfaces. These crusts are often found on outdoor brick walls, water fountains and other areas where brick is exposed to water. The crusts are a deposit of hard mineral salts consisting of calcium, magnesium. These minerals originate from the soil, setting bed or from the water itself. These salts are similar to efflorescence in that they are a mineral. They differ in that they form a hard crust that can be difficult to remove.

 

Now imagine all these salts trying to escape the surface of the brick. As the salts being carried by water migrates to the surface and meets the paint of coating, they become trapped.  The salts continue to accumulate in the pores of the brick and slowly attack the brick causing the paint to flake and the brick to break down and in server cases turn to powder. At this point replacement may be the only option.

In conclusion if painting brick or applying any sealer or coating it is important to make sure the paint, sealer or coating is breathable. Most paints and sealers are not.