NPT StoneScapes Regular Pebbles PEBBLK610-50 47-50 lb 6-10 Regular Black Pebble is used to repair cracks or damages that occur in pool and spa foundations. Made from a blend of cement and natural aggregates, pebbles are extremely durable. Using pebbles is good maintenance for pool finishes, and can help prevent more expensive future repairs. Pebbles have an extremely strong bond strength, and will not shrink after installation.