How to Install a Thimble in Cement Block Chimney

Installing a thimble in a cement block chimney is a task that requires careful preparation, safety precautions, and proper installation techniques to ensure the safety and functionality of your wood stove or fireplace. Here's a step-by-step guide to help you install a thimble in a cement block chimney:

Note: Before starting any work, ensure you have the necessary safety equipment, including gloves, safety glasses, and a dust mask. Consult local building codes and regulations for any specific requirements or permits needed.

Materials and Tools Needed:

- Pipe thimble (ensure it fits your stovepipe size)

- Drill with masonry bits (various sizes)

- Hammer

- Chisel

- Level

- Pencil or marker

- Tape measure

- Safety equipment (gloves, safety glasses, dust mask)

Step 1: Preparation:

- Locate the desired location for the thimble in the cement block chimney. If you have an existing thimble, you may want to replace it in the same spot.

Step 2: Measuring:

- Measure the outside diameter of the thimble.

- Mark a circle on the cement block chimney at the desired location, aligning with the center point.

- Ensure that the circle is slightly larger than the thimble diameter to allow for room to insert it.

Step 3: Drilling Guide Holes:

- Using a masonry drill bit slightly smaller than the thimble diameter, drill pilot holes around the marked circle.

- Drill several holes along the circumference, forming a guide for chiseling.

Step 4: Chiseling:

- Use a hammer and chisel to carefully remove the cement blocks from the center of the circle, working your way towards the guide holes.

- Gradually enlarge the hole until it's slightly larger than the thimble's diameter.

Step 5: Fitting the Thimble:

- Check if the thimble can be fitted into the opening. If any debris or uneven surfaces hinder its insertion, use the chisel to remove any obstructions.

Step 6: Leveling the Thimble:

- Place the thimble in the opening and check that it's level both vertically and horizontally using a level tool.

- Make adjustments by chiseling the cement blocks as needed.

Step 7: Securing the Thimble:

- Use mortar or a suitable sealant to secure the thimble in place. Apply the mortar or sealant around the outer edges of the thimble, ensuring it's well-sealed to prevent air and moisture from entering the chimney.

Step 8: Finishing Touches:

- Clean up any excess mortar or debris.

- Let the mortar or sealant dry completely according to the manufacturer's instructions.

Now, you've successfully installed a thimble in the cement block chimney. Remember to follow local regulations and guidelines and take necessary safety precautions when working with cement and masonry. If you're unsure about any step or have concerns about your specific chimney setup, it's best to seek professional help.