While Limestone can grow and shrink with the weather, it is durable enough to survive being outside. There is a very rare possibility that if this stone was covered in heavy precipitation, then temperatures hit below freezing and then you dropped a heavy object on them the next morning; they might be susceptible to cracking then. The Lincoln Memorial is made with Limestone and the Great Pyramids has an outside cover made of Limestone, making it a very durable decision for your porches!