Problems With Shadowing When Installing Drywall

Visible Ridges

• Shadowing can refer to visible ridges along taped seams on walls and ceilings. Joint photographing is another common term for this type of defect. Drywall workers embed paper tape where boards of drywall meet, using joint compound to form a bond. If a worker fails to wipe the tape flat, the taped seam might be visible after painting. Repair entails applying several thick coats of joint compound over each side of the ridge, raising the level of the surrounding areas to match the prominent ridge.

Dark Lines

• Shadowing also might refer to dark lines that run in line with the wood joists of the room’s ceiling. The cause is condensation, which traps moisture and occasionally causes mold growth. Condensation occurs more often in these areas because areas of drywall directly below the wood joists experience lower temperatures than areas between the joists, which likely are protected from winter temperatures by a thick layer of insulation. To hide the dark lines, clean the ceiling with mild soap and clean water and apply a fresh coat of paint.

Insulation

• Add a new layer of insulation above the ceiling to prevent future shadowing problems. The new layer should rest perpendicular over the ceiling joists rather than between them. This shields the tops of the wood joists from the winter cold, preventing the temperature differential across the drywall ceiling below and corresponding problems with condensation.

Texture Shadowing

• Texture shadowing occurs when painted drywall has visibly different textures in adjacent areas. Typically, its only apparent in brightly lit areas. The problem results from the texture difference between bare drywall, which has a light fuzz, and finished areas of drywall, which are smooth because of multiple coats of joint compound. Prevent texture shadowing by applying several light skim coats over the entire surface of the drywall boards, rather than limiting the compound applications to seams and screw heads.