The only approach that normally makes sense on most retaining walls is a ventilated panel system using composite aluminum panels such as Dibond on galvanized or stainless steel furring strips (aka hat channels) with an air gap at the bottom and top, with an overhanging aluminum flashing at the top to prevent precipitation from getting behind the panels. This isolates the mural substrate from the moisture issues, and promotes drying behind the panel due to air movement from convection (the chimney effect). The panels can be fastened through the face with pre-painted rivets. This will of course raise costs, but the panels are very tough and moisture will become a non-issue. Aluminum and acrylic paint have the same coefficients of expansion and contraction. Careful surface prep of the aluminum and use of a good bridge primer are required.
- William Cochran, Cochran Studio, Frederick MD

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