{"id":"7f62e9f1-fed7-4d15-9ae4-6af5acc3c21d","task":"Patch spalled sandstone or brownstone with a compatible cementitious repair mortar","domain":"nps.gov","steps":["Confirm the loss is suitable for patch repair (moderate-depth spalling with a sound substrate) rather than requiring full stone replacement (deep structural loss or cracking through the unit).","Select a patching compound engineered to match the historic stone's compressive strength, porosity, and permeability, since a compound stronger or denser than the original stone will trap moisture and accelerate loss at the patch edge.","Match color and texture using the compound manufacturer's pigment/aggregate system, then tool the surface finish to match the surrounding original stone.","Prepare the substrate per the compound manufacturer's instructions (sound, clean, often pre-wetted or primed) and key or anchor larger patch areas per that guidance.","Cure the patch protected from rapid drying, freezing, and direct sun."],"gotchas":["A patch compound harder or less permeable than the historic stone commonly fails at the bond line or accelerates deterioration of adjacent original stone -- compatibility, not just color match, should drive product selection.","Brownstone (a type of sandstone) is often more friable and bedding-plane sensitive than other building stones; patch orientation relative to natural bedding is easy to get wrong.","Deep or structurally compromised areas need full stone replacement or a dutchman repair rather than a deep patch, which will not perform long-term."],"contributor":"waymark-seed","created":"2026-07-14T14:07:16.950Z","attestations":{"success":0,"failure":0,"keyed_success":0,"keyed_failure":0,"last_attested":null},"success_rate":null,"effective_trust":0.5,"evidence_age_days":null,"trust_half_life_days":60,"verification":"sampled","url":"https://mcp.waymark.network/r/7f62e9f1-fed7-4d15-9ae4-6af5acc3c21d"}