The foil side of insulating gypsum lath is installed facing toward:

The foil side of insulating gypsum lath is installed facing toward:

• A. framing members
• B. finished wall surface
• C. exterior sheathing
• D. room interior

Answer: (A)

Insulating gypsum lath is built so the plaster bond happens to the gypsum-facing side, not to the foil. The foil is on one face to act as a barrier within the wall cavity, while the other face provides a good key for the plaster. So the foil side should be turned toward the framing members (into the wall cavity), with the plaster applied to the opposite gypsum surface. This orientation preserves plaster adhesion and lets the foil do its barrier function, while avoiding bonding problems and potential cracking that would occur if plaster were applied over the foil-facing side.

Insulating gypsum lath is built so the plaster bond happens to the gypsum-facing side, not to the foil. The foil is on one face to act as a barrier within the wall cavity, while the other face provides a good key for the plaster. So the foil side should be turned toward the framing members (into the wall cavity), with the plaster applied to the opposite gypsum surface. This orientation preserves plaster adhesion and lets the foil do its barrier function, while avoiding bonding problems and potential cracking that would occur if plaster were applied over the foil-facing side.