Dried plaster or mortar splatter on an exterior plaster surface can be stubborn, but the safest removal method depends on the finish underneath.
Wet the dried material thoroughly with clean water and allow it to soften. Use a plastic scraper and a stiff nylon brush to loosen the residue. Avoid metal scrapers, which can scratch or gouge the finished surface.
When water and mechanical cleaning are not enough, a professional masonry cleaner formulated to remove mortar smears may be appropriate. Products such as PROSOCO Sure Klean 600 are acidic cleaners intended for masonry applications. Always follow the manufacturer's dilution, application, safety, and rinsing instructions, and test a small inconspicuous area first.
Do not assume an acid cleaner is safe for lime plaster, limewash, Venetian plaster, Marmorino, or other decorative mineral finishes. Acid can etch, discolor, or permanently alter these surfaces. On specialty finishes, identify the material first and use the gentlest compatible cleaning method.
Exterior plaster systems vary widely. A small test area can prevent a cleaning problem from becoming a refinishing project. For specialty plaster and decorative wall finishes, California Wall Design recommends evaluating the substrate and finish before using aggressive chemical cleaners.
A personal update from Tim Jordan on a busy season at California Wall Design, his appearance on The Aggregate podcast, a week learning Tadelakt in Bozeman, and remembering fellow plasterer Rik Cirignano.
