Painters and carpenters apply this protective layer to the hidden side of exterior wood products to block moisture absorption from the wall cavity. Sealing all six sides of a board prevents uneven expansion and contraction, which causes cupping, warping, and premature paint failure on the finished face. It is a critical step for longevity in humid climates or when installing cedar and redwood.
Heard on the job
If we don't backprime those fascia boards before they go up, the morning dew will rot them out in five years.
Also heard as
- back-seal