Record where the deposit appears
Photograph the affected area from a safe location and note whether the material follows joints, runs below mortar, concentrates at sheltered areas or appears broadly across a slope. Note recent repairs and weather. Surface deposits can have different causes; color alone does not prove a tile manufacturing defect or establish the condition of the underlayment.
Investigate moisture and materials
Soluble salts and moisture movement can produce deposits, including deposits associated with mortar. A roof specialist should consider adjoining materials and water paths before recommending cleaning or replacement. Compare affected and unaffected areas. Keep any proposed diagnosis connected to observed evidence rather than assuming that all white marks are the same substance.
Choose a restrained response
Do not start with acids, abrasive tools or high-pressure washing. Those approaches can damage surfaces or adjacent materials and may not address the source. Obtain product-specific advice and test any approved cleaning method on a small unobtrusive area under professional supervision. Preserve photographs before treatment, and include any drainage or mortar correction in the written repair scope.
Further reading & technical sources
- National Park Service · Preservation Brief 30 ↗
- Tile Roofing Industry Alliance · Technical briefs ↗
- GSA · Repair and reattachment of clay roof tile ↗
Consult the current product documentation and local requirements for your project. These introductions are not installation specifications.
More tile roofing guides
- Crazing, chips and spalling on clay tile
- Reading historic clay tile maker’s marks
- Documenting a historic clay roof before work
Tile Roofing USA editorial guide · Published October 28, 2026.