Started adding mortar to the bricks. The building has a many levels of brick work greatly complicating putting mortar lines in. I first tried some house hold latex wall paint, but the results were terrible. I went back to my Joint Compound method that I've used several times before. I added some Mars Black tube acrylic artist paint to make it more gray and overdid it, so I knocked it back with some white paint of the same type.
This little bit is all the compound I have left. I have to get more at the hardware store.
I was first slathering it on with a palette knife and then using a single-edged razor to scrape off the excess, but changed by putting a blob of the joint compound at the start of the area getting mortar and using the razor to squeegee the "mortar" down over the area which did the spreading and scraping in one operation. I then used a #11 blade ground to a broad/flat edge to remove excess in the corners of all the various height areas.
I finished one side in about 2.5 hours. It's a slow, annoying process, but it makes a huge difference in the ultimate appearance of the model. When I do the hardware store, I'm going to paint and mortar the layers before I glue them together making it go much faster. When this part is done, I'll use an alcohol wash to dull it down a lot. There are masonry and top details that will be concrete color. I will mask and paint them when all the mortar work is done. The molded-in door will be painted the UP Armor Yellow window color. If I was going to leave the windows clear I would have to put in floors and a core with elevators and stairwells. The building is so narrow that a core almost wouldn't actually fit.
