Reset a loose brick
When a brick works loose, you can't just shove mortar in around it and expect the repair to last. Pull it out and fix it right.
It'll take you at least 20 minutes to remove a loose brick from a wall and clean off the old mortar from both the wall cavity and brick. If possible, reuse the old bricks. New brick will never match the texture or aged color of the original.
When resetting bricks, follow these guidelines:
Visit your local hardware store or builder's merchant and ask for bagged mortar mix, not sand or concrete mix.
Wear safety glasses. Also wear waterproof gloves; mortar contains alkaline chemicals that can burn you.
Mix small batches of mortar. Hot, dry weather and direct sunlight can reduce the viable working time of the mortar from 60 minutes to 30.
Immediately clean mortar smears off brick faces using a soft-bristle brush (a wire brush may leave rust marks). If the mortar dries, you'll have to use chemicals to remove it.
You will need:
Hammer and flat chisel
Small, stiff brush
1. Chip away the old mortar with a cold chisel or flat utility chisel. Hold the chisel at a low angle, work it in under the mortar and hit the chisel with short, light hammer blows. Dust out the cavity using a stiff broom and dampen it with water to improve mortar adhesion.
2. Knock the mortar off the old brick by holding the chisel at a high angle and hitting it with rapid, light blows while moving the chisel tip quickly over the surface of the hardened mortar. Clean the brick with a wire brush and rinse it off with water.
3. Apply a 20mm layer of mortar to the bottom, both sides of the cavity and the top of the brick. Slide the brick into the cavity.
4. Pack the mortar oozing from the joints with a brick trowel and pointing tool. Add more mortar by sliding it directly off the trowel and into the joint. Finish the joint surfaces to match the shape of adjacent joints.