John Schaub says:

Spray your model kit brick walls with satin surface paint. Depending on where your layout is located.
Primer Red or Rusty Red Primer looks close to brick. Let it dry for at least 48 hours, Once its dried,
lay out the walls on a flat surface. Using hobby paint specific for model building. Water base. There’s multiple colors to work with. Polly S made by Floquil is the best paint to use. It might be hard to find this paint as the company no longer produces it, A hobby retailer might have it in stock. Colors to look for are: aged concrete, depot buff or aged white. Take a small amount of the paint. add a small amount of water to the brick and mortar lines. The water will let the paint naturally run down the mortar lines. If you don’t like the results. Try it again and again. It looks realistic once you get the technique down. Let the paint dry before you hold up the wall vertically. Once dry, you can wipe off the paint off the bricks. The results can vary just as the prototype does. Good luck with
the experiment.