You can change a room by painting a brick fireplace, but there's more to it than rolling on a can or two of latex. The rough, irregular surface of brick requires some forethought about methods and materials. And since your goal is improve the look of the fireplace, you must approach the task with a designer's eye, thinking about the various tones and shadows present in natural stone. With layering techniques, good supplies and an understanding of how your brick will react to paint, your fireplace will be a valuable addition to the room.
An important first step is a careful examination of your fireplace. Look for cracks and chips -- the deep ones might be hard to get to. If you have any moisture in the mortar, have it sealed before painting. Gauge the durability of the brick -- softer, more porous brick pocked with indentations will react differently than a harder, smoother brick. Try to determine the age of your brick. If it is new, it should not be painted at all: Acording to Rick Watson of Sherwin-Williams, new brick requires at least a year to dry and leach. Older brick might be more acidic and cause paint to fade. Test out paint products in a hidden area of the fireplace.
The supplies you need depend on your strategy. You could purchase an interior brick-painting kit -- such as Brick Anew -- that includes all materials and instructions. If not, the most important decision is the kind of paint you will use. Latex provides good coverage, but it could peel away from some types of brick. Get a sample and test it out first. Another approach is to paint the brick with a primer designed for masonry -- Loxon by Sherwin-Williams is one example -- and then use acrylic or latex over it. You can also use a paint and primer combination and skip the extra work involved with priming. You will want two contrasting shades of paint in order to achieve the natural stone effect -- perhaps an off-white and a light gray. Other supplies include paint rollers, trays, tape and sponges.
Painting the Base
Clean the brick with trisodium phosphate (TSP) before painting. If you decide to prime, roll on two coats. Before putting on the first application of paint, measure the size of your bricks and cut a few cellulose or craft sponges to fit exactly, minus the mortar. At this point, you must decide what your natural stone effect will look like. If you want light gray bricks with off-white mortar, then use off-white as the base. Apply the base paint with a roller, making sure that every crevice is coated. Use a brush to fill in stubborn spots. Alternately, you could use a paint sprayer for this step. Allow the paint to dry for 12 to 24 hours.
Painting the Stone Effect
The final, fun step is to apply the stone texture to the base layer. Pour your contrasting paint into a tray. Wet the brick-sized sponges with water and squeeze them out. Have two or three sponges -- all made from the same material -- on hand. Dip a sponge gently into the paint tray and press it on a cardboard tester. Experiment with different levels of pressure. When you have a feel for it, use the sponge on a brick. Make sure to stay inside the brick boundaries -- don't venture away or you will paint the mortar and ruin the effect. If you make a mistake, wipe it away immediately. Stamp every brick in the fireplace, using different sponges and levels of pressure. Don't worry if some of the base layer shows through -- that's supposed to happen. You will see the stone effect emerge as you work.