North Carolina General Contractors Practice Exam

How can you increase the compressive strength of mortar?

1. By adding sand

2. By using more water

3. By adding cement

4. By changing the lime type

The correct answer is: By adding cement

Increasing the compressive strength of mortar can be effectively achieved by adding more cement to the mix. Cement is the primary binder in mortar, and its main role is to provide structural integrity and strength. When the quantity of cement is increased, the resulting chemical reactions—specifically, the hydration process—produce more calcium silicate hydrates, which contribute significantly to the material's strength. In contrast, the other choices do not contribute positively to compressive strength. Adding more sand dilutes the cement content and can reduce the overall strength. Increasing the water content, while sometimes necessary for workability, can lead to a weaker mix due to higher porosity if not managed properly. Changing the type of lime may affect flexibility and workability, but it does not inherently increase compressive strength as effectively as increasing the cement quantity does.