Ratka Rhyolite is a type of stone found in Hungary that is commonly used for various applications such as flooring, wall cladding, and countertops. While it is a durable and hardy material, its suitability for exterior applications in very rainy climates may depend on several factors.

1. Porosity: Ratka Rhyolite is a volcanic rock with variable porosity. If the stone has a high porosity, it may absorb water, leading to potential issues in very rainy climates. Water absorption can cause the stone to weaken, crack, or stain over time.

2. Freeze-thaw cycles: In regions with very rainy climates, freezing temperatures can exacerbate the effects of moisture on stone surfaces. If water is absorbed into the stone and then freezes, it can cause the material to expand and contract, leading to cracking or degradation.

3. Sealing: To enhance the stones resistance to moisture and staining, it is typical to apply a sealant on Ratka Rhyolite. This can help mitigate water absorption to some extent. However, it is essential to select a high-quality sealant and periodically reapply it to ensure optimal protection.

4. Maintenance: Regular cleaning and maintenance are crucial for any exterior stone application, particularly in rainy climates. Standing water or debris can expedite the stones deterioration, so it is important to keep the surface free from moisture and maintain proper drainage.

Considering these factors, Ratka Rhyolite may be suitable for exterior applications in very rainy climates if the stone is of low porosity, properly sealed, and maintained regularly. However, it is recommended to consult with a local stone professional or geologist who can assess the specific characteristics of Ratka Rhyolite available in your area and provide tailored advice based on the climate conditions.