- 1). Clean the existing fire-brick joints and remove the crumbling mortar. Chip away the loose mortar with a brick hammer and chisel, being careful not to chip the brick. Vacuum the mortar from the fire box. Brush the joints with a wire brush. Wear a dust mask and eye goggles while cleaning the brick joints.
- 2). Add eight shovelfuls of brick sand to a wheelbarrow. Place the 1/4-inch screen wire over the wheelbarrow and place the sand on the screen. Shake the sand into the wheelbarrow to remove small stones and debris.
- 3). Add 1/2 bag of fire mortar to the wheelbarrow. Purchase the fire mortar from most any brick and block supply company that furnishes specialty items. Blend the sand and mortar with a hoe. Stand at the rear of the wheelbarrow, pushing and pulling the mixture until it is completely blended. Add 3 gallons of water to the mix and blend until you have a pancake-batter consistency.
- 4). Add the mortar to a masonry grout bag, which is found at any hardware store. The grout bag resembles a cake decorating bag. Scoop up the mortar from the wheelbarrow with a mason's trowel and place the mortar in the grout bag.
- 5). Wet the existing joints of the fire brick with a spray bottle filled with water. Place the tip of the grout bag into the joints and squeeze the bag from the top, forcing the mortar out the tip and into the masonry joints. Fill the fire brick joints to just above the surface of the fire brick.
- 6). Allow the mortar to set for 30 minutes. Smooth the mortar with a thumb jointer, also found at most hardware stores that supply masonry tools. The thumb jointer is a 3/8-inch cylindrical tube. This tube, concave on one side, fits against the thumb as you hold it in your hand and is dragged across the mortar joints until they are smooth. Use this tool to create a smooth, concave fire brick joint. Sweep the joints with a soft-bristled brush.
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