Metal flashing is the first line of defense against water intrusion. It seals the gaps around chimneys, vent pipes, roof valleys, and even exposed windows. If you skip maintenance, those seals fail. Inspect your roof every spring. Look for thin spots or gaps at the joints. If you find them, cover the entire joint with roof cement. Apply it generously. Use a trowel to spread it thick. The edge of the flashing must be completely covered.
Chimney flashing is tricky. It has two parts. A base piece sits on the roof. A cap piece is mortared into the chimney bricks. When the mortar crumbles or the flashing pulls loose, water gets in. You need to resecure it.
How to Resecure Chimney Flashing Step-by-Step
Start by pulling the lip of the cap flashing out of the mortar joint. Only pull as far as it comes easily. Do not yank it out. Do not pull it completely away from the chimney. The less you separate it, the easier the repair will be.
Next, clean out the old mortar. Use a hammer and chisel. Wear safety goggles. Your eyes need protection from falling debris. Then use a wire brush to clean the joint. Be careful not to damage the metal. Remove all debris.
Wet the joint with a paintbrush dipped in water. This helps the new mortar bond. Use a small trowel to fill the joint firmly with cement mortar. Pack it in tight.
When the joint is full, press the lip of the flashing back into the mortar. Put it in the same position it was in before. Press it in firmly. Do not push too far. If you push too hard, it may pop back out. Then you start all over. Let the mortar dry as directed.
Final Sealing and Vent Pipe Repairs
Once the joint is completely cured, caulk around it. Use butyl rubber caulk. Cover the joint and the lip of the cap flashing. This adds an extra layer of protection.
Check vent pipes too. Make sure the joint at the base is sealed. Look for gaps at the roof line. If you see gaps, caulk around the base of the pipe or chimney. Use roof cement in a caulking gun. Vent pipes on pitched roofs usually have a protective collar. If the collar is loose, tap it back into place. Caulk the base joint with roof caulk.
Tools You Will Need
Fixing metal flashing around a chimney requires specific tools. Have these ready:
- Hammer
- Chisel
- Safety goggles
- Wire brush
- Paintbrush
- Water
- Cement mortar
- Small trowel
- Butyl rubber caulk
There is always more to learn about flashing. Specifically the type used around a roof’s vent pipes. That is a different story entirely. For now, focus on getting that chimney sealed. Water waits for no one.
