Yes, China Grey Slate can be used for exterior applications in very rainy climates. Slate is a natural stone that is known for its ability to withstand various weather conditions, including heavy rain and moisture. It is resistant to water absorption and does not become easily damaged or degraded by continuous exposure to rain or moisture. Additionally, the natural texture and slip-resistant surface of slate make it a suitable choice for outdoor applications in wet climates. However, proper installation and the use of a suitable sealer may be necessary to ensure the slate remains durable and maintains its appearance over time.