We have a 150-yr old home in Michigan. We just had the old Transite siding removed, revealing the original clapboard. A professional painter friend suggested that the siding might have originally been painted with milk-based paint. He said the casein would inhibit adhesion, rendering the current siding unpaintable (there is a lot of crazing on the surface in spots). Also, stripping the milk paint is nearly impossible (I could only do this on interior doors by taking them to someone having an acid bath). Obviously, we would prefer not to replace the otherwise intact original clapboard. What do you think of this? If is milk paint, is it unpaintable? Do we need a lab test to determine whether the old paint contains casein? Is there a reasonable means to remove the old paint; can sanding result in a well-prepared surface? We need to decide what to do within the next month or so. I appreciate your considered advice - thanks.

i am painting a 27' wall that is common for the dining room and living room............i would like to find a way to break the 2 different colors