Having a flaking, cracking, or discolored concrete surface can make your property look unattractive and poorly maintained. Many of our homeowner and business clients come to us asking if you can put asphalt sealer over concrete surfaces to protect their driveway or parking lot? The misconception here is that because asphalt and concrete are used in creating paved surfaces, that the two materials are interchangeable. However, their different properties, installation methods, and maintenance requirements, means they should not be treated the same. Applying asphalt sealer over concrete isn’t recommended as it won’t adhere properly, won’t provide any benefits, and can have negative consequences.
What Are The Differences Between Asphalt and Concrete?
While both asphalt and concrete are made from aggregates (sand, gravel, or crushed stone), and have a binder, the main difference lies in the type of binder used. Asphalt uses a petroleum-based binder (bitumen) which is a sticky substance derived from crude oil, while concrete uses a cement-based binder, which is a powdery substance made from limestone and clay. The difference in these binders is what gives asphalt and concrete their performance, durability, and overall properties, and is what makes them incompatible with one another. For example:
- Asphalt is flexible, resilient, and can expand and contract with temperature changes. Concrete is rigid, durable, and can withstand high compressive forces.
- Asphalt allows water to seep through its surface (porous). Concrete blocks water from penetrating its surface (impervious).
- Asphalt is dark in color, which absorbs heat and melts snow and ice faster. Concrete is light in color, which reflects heat and allows it to stay cooler
These differences in composition result in contrasting properties, and is why concrete requires different sealant treatments.
What Is The Purpose and Composition of Asphalt Sealer?
Asphalt sealer is a protective coating that is applied over asphalt pavement to extend its lifespan and improve its appearance. It consists of refined coal tar (asphalt emulsion), water, sand, clay, polymers, and additives, and works by filling in the pores/cracks present in the asphalt’s surface. The sealant’s smooth and uniform layer prevents water, oil, and chemical contaminants from penetrating the surface, and blocks UV rays so that the bitumen binder doesn’t become oxidized and degrade.
The Incompatibility With Concrete
So, can you put asphalt sealer over concrete? No, the sealer is incompatible with the concrete’s surface texture and lack of porosity.
1. Asphalt sealer is not compatible with the cement binder in the concrete. The chemical reaction between the two materials can cause the sealer to peel off.
2. Asphalt sealer isn’t designed to adhere to a smooth and hard surface. The sealer won’t penetrate the concrete’s surface or form a strong bond, leading to premature failure.
3. Asphalt sealer is not suitable for the thermal properties of concrete. The sealer won’t expand and contract with the concrete surface, hindering the concrete’s ability to move. This can lead to delamination, and a compromised appearance.
What Are The Potential Consequences Of Misapplication?
Using asphalt sealer over concrete can have negative effects and deal damage to the concrete’s surface. Consequences of misapplication are:
- The sealer won’t provide any protection to the concrete, and instead create a thin and weak layer on top that will wear off quickly.
- The sealer will interfere with the proper drainage of water from the concrete surface, trapping water underneath and causing moisture problems like spalling, freezing and thawing damage, and the formation of a white powdery substance on top (efflorescence – from salt deposits.
- Asphalt sealer can create an uneven, patchy, and dull finish.
- The sealer will waste time, money, and resources that could have been used for more effective concrete surface sealants.
As you can see, putting asphalt sealer over concrete isn’t recommended if you want to protect your concrete surfaces from the harsh elements and extend their lifespan. Instead, you should consult with a professional concrete contractor who can apply the best sealant for your specific situation. For concrete, acrylic, epoxy, polyurethane, silane, siloxane, and silicate sealers are effective, and we have them all here at DCPLM in Orlando, FL. Contact us today to learn more and let us help you preserve your concrete investment.