Final answer:
Small horizontal cracks in a stucco wall every 3 feet are due to thermal stress caused by temperature fluctuations. These cracks occur as the stucco expands and contracts with changes in temperature. Incorporating expansion joints in the stucco wall design can help minimize these cracks.
Step-by-step explanation:
Small horizontal cracks approximately every 3-feet in a stucco wall are due to thermal stress. When a stucco wall is exposed to fluctuations in temperature, it expands and contracts. Over time, this can cause small cracks to form.
Thermal stress is a result of differential expansion and contraction due to temperature variations. The stresses created by thermal expansion can cause materials like stucco to crack.
Similar to how plaster walls crack as a house warms and cools, stucco walls can experience the same phenomenon. To prevent or minimize these cracks, expansion joints can be incorporated into the stucco wall design to accommodate for thermal expansion and contraction.