Why does permeable rock weather faster than a rock that is not permeable?

Permeable rock tends to be sedimentary rock, formed by silt deposits building up over long periods of time. They tend to be softer than igneous rock which are normally not permeable.

Softer rock is worn faster than hard rock but additionally, the absorption of water can also contribute to weathering, especially in regions where the water can freeze and thaw within the rock. The freezing of water causes the rock to crack and loosen, so hastening the loss of solid rick. Igneous rock does not absorb water and so suffers damage due to ice far less than sedimentary rocks.