Water, over time is a very powerful force and while wind can cause erosion over time water is the main agent of erosion on this planet. The deal with the Grand canyon is that the colorado river has carved out what you see however that is complicated by uplift which has been going on which also contributes to it. If you take granite for example it's mostly made of quartz, feldspar and mica. (There are actually several different types of granite) The mica goes first turning into basically mud and that's carried away by water mostly. That leaves cracks and pits and water gets in and from freezing and/or water the feldspar goes next and by then there is just the quartz which turns to sand and that gets carried away.

As far as sedimentary rocks being glued together some do have another mineral or combinations of minerals which hold it together but oftentimes its the pressure over time that just compresses it and there is no glue. In certain areas you will see rock strata that is not actually rock yet it still very soft and is in the process of becoming a sedimentary rock. Maybe in a few million years or so that's what you will have.

Clear as mud? har har.