We recently bought an older home (built in the early 1900s), and it has the old lath and plaster walls. The main floor walls look great, no reason to replace them right now. The problem is the 2nd floor (upstairs). About 75% of the plaster has crumbled off of the lath. My question is how should we go about remodeling up there? The floors and walls are solid. Can we just plaster over the lath? Or would it be easier to just drywall?