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A.  General Information
B.  Chimney Maintenance
C.  Chimney Repairs

A. General Information
chimney-fireplace_3-D-view The basics of a chimney. The major parts of a chimney include the stack, flue, and crown. The stack is the visible outer shell of the chimney, usually made from masonry (brick, block, stone, etc.). Inside the stack are flue(s), which are the empty spaces or channels that let the rising gases escape. There is always a separate flue for each item being vented. Protecting the inner walls of a chimney is a concrete or steel liner. The chimney crown is at the very top of the chimney and is often made of mortar and seals the space between the edge of the stack and the flues. Crowns are prone to cracking and chipping because of the extreme temperature changes they must endure. You need to inspect and repair the crown when there are obvious cracks that might make the chimney vulnerable to more damage and eventual deterioration. You can use a pair of binoculars to make a quick inspection of the chimney without going on the roof. Check for cracks, sags, or other signs of deterioration. You might need to hire professionals to inspect flue liners or do larger masonry repairs, but if you don't mind working at heights, it's possible to do chimney maintenance yourself.

B. Some maintenance tips
According to the National Fire Protection Association, chimneys should be inspected once a year. When inspecting, check for animal nests or other obstructions, cracks in the flue or masonry, and deposits of creosote (a flammable, tarlike substance created by burning wood). Also, look for a buildup of soot in the flue. Even as little as ¼" of buildup can restrict airflow and lower the performance of your chimney. To clean, rent a chimney brush that matches the width of the inside diameter of the flue. Open or remove the damper and seal the fireplace opening with plastic or an old blanket. Working from the roof, insert the brush into the flue and push downward. Gently work the brush up and down, scrubbing hard enough to remove soot but not hard enough to damage the liner or mortar. Add extension handles until the brush reaches fireplace opening.

maintenance In cases where it is not possible to work from the roof, you must accomplish the task from the inside. Insert the brush through the fireplace opening and work it up the flue. Let dust settle for an hour, then lay a dropcloth around fireplace opening and remove the seal. Use a stiff-bristle brush, like a toilet brush, to remove soot and debris in the firebox, especially in mortar joints and around the damper

C. Repairs
chimney_repair Repairing your chimney will require a certain amount of "Trade-Sense" (experience with masonry tools and mortar). The most common brick and block repair is "tuckpointing", the process of replacing failed mortar joints with fresh mortar. Cracked or missing mortar can let moisture into a chimney structure and can cause additional damage. Start by using a mortar raking tool to clean out loose or deteriorated mortar to a depth of ¼" to ¾". If mortar is stubborn, use a masonry chisel and hammer. Clean away all loose debris, then dampen surface with water. Mix the mortar, adding concrete fortifier and, if needed, pigment to match existing mortar joints. Mix it to a consistency that slides slowly off a trowel. Load mortar onto a mortar hawk, then push mortar into the horizontal joints with a joint filler. Apply mortar in ¼"-thick layers, allowing each layer to dry for 30 minutes before applying the next layer. Fill joints until the mortar is flush with the face of the brick. Apply the first layer of mortar into the vertical joints by scooping mortar onto the back of a joint filler and pressing it into the joint. Work from the top downward. After the final layer is applied, smooth the joints with a jointing tool that matches the profile of the old mortar joints, tooling the horizontal joints first. Brush off excess mortar with a stiff-bristle brush. Periodically mist the repair area with water, or cover it with damp rags for several days to slow down the drying time and strengthen mortar's bond.

chimney-crown-installation

If the crown is badly damaged, or if cracks recur, consider building and installing a floating chimney crown. It is less prone to cracking because it's not attached to the chimney and provides a drip edge that directs runoff and helps protect the mortar and brick from deterioration. To build a floating chimney cap, measure chimney stack and flue and build a form from ¾" plywood. The form should be 4 ¾" high in the center and 3 ½" high at the outside edge and should extend 2" beyond the chimney on all sides. Using 1 ½" wood screws to connect the parts, attach the form to a plywood base. To form a drip edge, make a frame from 3/8" dowels, then glue it 1" from the edges of the form. Prepare a stiff batch of mortar mix and fill the form. Rest a wood float across edges of form and smooth off the cement. Keep angles sharp at the corners. Let the crown cure for at least two days, then carefully disassemble the form. Chisel away the old crown and clean the top of the chimney with a wire brush. Set the new crown directly on the chimney and center it so the overhang is equal on all sides. Adjust the crown so the gap around the flue is even on all sides, then fill that gap with fire-rated rope or mineral wool. Caulk over the fill material with a very heavy bead of fire-rated silicone caulk. Also, caulk the joint underneath the crown. Inspect the caulk every two years and replace it when needed.