Application is a layered affair, especially for deep repairs. The prepared cavity is first dampened (but not soaked) with clean water to prevent the dry stone from sucking moisture out of the new mortar too quickly. The repair mortar is then pressed firmly into the cavity in thin layers, no more than 10-15 millimeters thick. Each layer must be compacted and left to partially cure (a process called “fettling”) before the next is applied. This prevents shrinkage cracks and ensures a monolithic bond. Once the final layer is built up slightly proud of the original surface, the real craftsmanship begins. Using wooden floats, sponges, and small modeling tools, the conservator compresses and shapes the wet mortar to match the original profile, tooling, and drip edge of the sill. A final, soft brush can be used to create a subtle sand-textured finish that mimics natural stone.