Protect the flooring. This is a dusty, dirty job. Remove all the furniture in the room, and place drop cloths over the floor. Tape the drop cloths with masking tape to keep them in place. You also need to wear safety glasses, a mask and gloves during this project.
Clean the wall. Remove any crumbling material and dirt from the wall before you begin. A whisk broom is helpful to clean surface dirt.
Parge the wall. An old technique that was used to cover bricks is called parging. This just means using regular brick mortar and covering the bricks. Mix your brick mortar in a bucket, and use a trowel to cover the bricks with a thin coat. Scrape off any excess as you work. Mortar takes time to dry, typically at least a day.
Plaster over the bricks. To give the wall a smooth, hard surface, you can plaster over the bricks. Mix plaster of Paris and water in a bucket. Load a small amount of plaster on to a hawk. Transfer some to a trowel and begin applying the plaster over the bricks. Work from the bottom up and sweep the plaster onto the wall. Smooth your trowel lines as you go, and make the surface as even as possible. Let it set for 30 to 45 minutes.
Sand the plaster. Getting an even coat is difficult with plaster, but you can sand away imperfections. Use a fine-grade sandpaper and preferably a hand block sander because it's easier to work with. Go over the wall until the entire surface is smooth. You can then paint and prime if you prefer or just leave the plaster natural.