Why Does Concrete Get Hot?
Concrete has high thermal mass. It absorbs sun all day and radiates it back at night. Lighter colors stay cooler.
Why Does Concrete Get Hot? Understanding Thermal Mass
Concrete gets hot in the sun because it has high thermal mass—it absorbs and stores heat energy. Understanding how this works helps you choose colors and finishes that stay cooler, and explains why concrete feels hot even after the sun goes down.
What is Thermal Mass?
Thermal mass is a material's ability to absorb, store, and release heat energy. Concrete has very high thermal mass compared to other building materials.
How It Works
- Absorbs heat: Concrete absorbs solar radiation throughout the day
- Stores heat: Heat energy is stored within the concrete
- Releases heat: Stored heat radiates back out, especially at night
Why Concrete Gets So Hot
Several factors make concrete particularly hot:
High Density
Concrete is dense, which means it has a lot of mass in a small volume. More mass = more capacity to store heat.
Dark Color (Usually)
Most concrete is gray or dark, which:
- Absorbs more solar radiation than light colors
- Converts more light energy to heat
- Gets hotter than light-colored surfaces
Low Reflectivity
Concrete doesn't reflect much light—it absorbs it. This means most solar energy becomes heat rather than being reflected away.
The Day-Night Cycle
Concrete's thermal mass creates a day-night temperature cycle.
During the Day
- Absorbs heat: Solar radiation heats the surface
- Heat penetrates: Heat moves into the concrete
- Temperature rises: Surface can reach 120-140°F+ in direct sun
At Night
- Radiates heat: Stored heat radiates back out
- Stays warm: Concrete remains warm even after air cools
- Gradual cooling: Takes hours to cool completely
How Color Affects Temperature
Color significantly affects how hot concrete gets.
Dark Colors (Gray, Black)
- Absorb more heat: Dark colors absorb 80-90% of solar radiation
- Get much hotter: Can reach 120-140°F+ in direct sun
- Radiate heat at night: Stay warm for hours after sunset
Light Colors (Tan, Buff, White)
- Reflect more heat: Light colors reflect 30-50% of solar radiation
- Stay cooler: Typically 20-30°F cooler than dark concrete
- Cool faster: Less stored heat means faster cooling at night
Solutions for Hot Concrete
If your concrete gets too hot, there are solutions:
Choose Light Colors
- Integral color: Add light-colored pigments to the mix
- Stained light: Use light-colored stains
- Painted light: Apply light-colored paint (though paint has other issues)
Add Shade
- Pergolas: Provide shade while maintaining open feel
- Umbrellas: Portable shade solution
- Trees: Natural shade that also cools the air
Use Reflective Sealers
- Light-colored sealers: Reflect more solar radiation
- Cool roof coatings: Specialized reflective coatings
Benefits of Thermal Mass
While hot concrete can be a problem, thermal mass also has benefits:
- Energy efficiency: In buildings, thermal mass helps regulate temperature
- Radiant heat: Warm concrete can heat surrounding areas
- Temperature stability: Reduces temperature swings
The Bottom Line
Concrete gets hot because it has high thermal mass—it absorbs solar radiation all day and stores the heat, then radiates it back at night. Dark colors absorb more heat and get much hotter (120-140°F+) than light colors, which stay 20-30°F cooler. To reduce heat, choose light colors, add shade, or use reflective sealers. Understanding thermal mass helps you make informed choices about concrete color and placement.
Need help choosing colors or finishes that stay cooler? Contact Local Concrete Contractor. We can help you select options that balance appearance with temperature comfort.
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