Phil all my brick foam board building have been been finished with sandtex masonry paints, and then a coat of matt varnish over the top works very well. The church is made from converted playmobil castle parts and 3D printed parts, at the moment sprayed with grey primer , as its all a trype of plastic I was thinking spraying would be the best as a base coat for it.
Beavercreek, that tunnels looking good, and I think your pics answer the basic question . I was worried the speckle size in the paint would look out of scale, but looking at your pics they do look like stone and to-scale, I haven't been weathering my buildings, I have left it to nature so far, your right a big single stone built church will need some I think, or it will look a bit toy like
Northsider I will remember that , in my case I think I will use a whole tin in one go to give it all a base coat , probally two tins in reality