Final answer:
Wood siding must be primed on all sides and ends before installation to protect against moisture and ensure paint adherence.
Step-by-step explanation:
The type of siding that must be primed on all sides and ends before installation is typically wood siding. Wood siding is porous and can absorb moisture, which may lead to wood rot and decay if not properly sealed.
Priming the siding helps to seal the wood, protect against moisture, and ensure that the topcoat of paint adheres properly.
It is especially important to prime end cuts, as they are more vulnerable to moisture penetration. Other types of siding materials, such as vinyl or metal, may not require priming because they are not as susceptible to moisture damage.
Priming is essential for longevity and durability, especially for end cuts that are more exposed to the elements.