What should I use to repair a chimney cap?

A chimney cap is a cover placed on top of the chimney to prevent water, animals, leaves, and other debris from entering the chimney. A chimney cap is an important part of a chimney system and needs to be maintained properly. If it becomes damaged or worn out, it can lead to a variety of problems such as water damage, draft issues, creosote buildup, and animals or birds entering the chimney. As such, repairing or replacing a damaged chimney cap in a timely manner is essential. But with different types of chimney caps available, it can be confusing to know exactly what to use to repair a chimney cap. This article will provide an overview of chimney caps, signs you need chimney cap repair, materials needed for repair, steps for repairing different types of chimney caps, and when to call a professional.

Types of Chimney Caps

There are several different types of chimney caps available:

Masonry Chimney Caps

Masonry chimney caps are constructed from concrete, stone, or brick. They are installed when the chimney is built and form an integral part of the overall chimney structure. Masonry caps are very durable but can become cracked or damaged over time.

Prefabricated Metal Chimney Caps

Prefabricated metal chimney caps are made from galvanized steel, copper, or stainless steel. They consist of a metal top with sides that fit over the existing masonry chimney crown. Prefab metal caps are relatively lightweight and easier to install than masonry caps.

Custom Copper or Stainless Steel Caps

Custom chimney caps are constructed on-site using sheet copper or stainless steel. The cap is sized and formed to fit the chimney crown. Custom caps allow for a perfect fit and unique designs.

Signs You Need Chimney Cap Repair

Some signs that indicate your chimney cap needs repair include:

– Visible cracks, chips, or holes in the cap
– Loose, damaged, or missing concrete or mortar
– Rust stains or streaks on the cap or chimney exterior
– Water leaks down the chimney and fireplace when it rains
– Animals, birds, insects entering the chimney
– Downdraft or smoking problems
– Moss, vegetation, or debris growth on the cap

If you spot any of these warning signs, it’s advisable to have the chimney cap inspected and repaired without delay.

Materials Needed for Chimney Cap Repair

The materials needed for repairing a chimney cap depends on the existing cap type and extent of damage. Some common materials include:

For Masonry Chimney Caps

– Concrete mix
– Mortar mix
– Bricks, stone, or concrete caps/crowns
– Masonry nails or screws
– Wire mesh
– Trowels for brickwork
– Grout sealant
– Chimney crown rubber membrane
– Masonry waterproofing sealant

For Prefabricated Metal Chimney Caps

– Sheet metal screws
– Sealant/adhesive
– Sheet metal panels, stainless steel, copper, galvanized steel
– Metal snippers for cutting and shaping metal
– Pop rivets, riveting tool
– Mesh screen material (for replacing damaged screen)
– Metal primer and touch up paint

For Custom Copper or Stainless Steel Caps

– Copper or stainless steel sheeting
– Solder and flux for copper work
– Pop rivets, riveting tool
– Metal cutting tools like snips, shears, tin-knockers hammer
– Rubber gasket or sealant
– Silicone caulk

How to Repair a Masonry Chimney Cap

Masonry chimney caps are usually installed when the chimney is constructed so they require rebuilding rather than quick repairs. Here are the general steps for repairing a masonry chimney cap:

1. Inspect the cap damage and determine repair scope – Look for cracks, holes, missing sections, deterioration. Identify all areas needing repair.

2. Remove any loose concrete or mortar – Use a chisel and hammer to chip away all cracked or crumbling material until you reach solid base.

3. Clean the surface – Sweep away debris then wash the surface with water and allow to dry completely.

4. Apply concrete bonding agent – Brush a concrete bonding agent over the repair area to improve adhesion. Let it cure per manufacturer instructions.

5. Build concrete/mortar mix forms – Erect forms around the chimney using wood, tape, or premade crowning forms. This contains the new concrete/mortar mix.

6. Mix and apply new concrete/mortar – Prepare mortar or concrete mix as per instructions. Apply over damaged areas 1-2 inches thick. Smooth with a trowel for slope.

7. Let concrete fully cure – Remove forms after initial curing. Allow new concrete to fully cure for several days as per product guidelines.

8. Seal with waterproofing sealant – Once fully cured, apply a chimney crown rubber membrane or masonry waterproofing sealer over the concrete cap.

9. Install drip edge – Use mortar to install a drip edge along the cap perimeter to prevent water from running down the chimney sides.

Following these steps will create a repaired masonry chimney cap that sheds water and withstands weathering.

How to Repair a Prefabricated Metal Chimney Cap

For prefabricated metal chimney caps, repairs involve refastening any loose panels, sealing joints, and replacing screening or rusty sections. Follow these basic repair steps:

1. Remove cap and inspect – Take off the metal chimney cap and look for problem areas like loose or missing fasteners, gaps, deteriorated flashing, and screen tears.

2. Clean surface – Wire brush any rusty sections on the cap or crown. Remove old caulk. Wipe down with solvent.

3. Replace screening – Cut and install new screening over any torn or damaged screen using pop rivets. Secure tightly.

4. Repair holes/gaps – Use sheet metal pieces with pop rivets or silicone sealant to patch over any holes or gaps in the cap panels.

5. Reseal joints – Run a bead of high-temperature silicone caulk along all the cap seams and joints. Also reseal the top crown edge.

6. Refasten panels – Check all screws, bolts, or pop rivets securing the panels. Tighten or replace as needed using new stainless fasteners.

7. Paint rust spots – Use a metal primer on any remaining rust spots followed by high-heat spray paint matched to the cap color.

8. Reinstall cap – Place the repaired metal chimney cap back on the chimney. Secure tightly.

These repairs should restore the cap back to functioning properly without needing full replacement. Monitor for any new leaks or issues.

How to Repair a Custom Copper or Stainless Steel Chimney Cap

For custom fabricated chimney caps made of copper or stainless steel sheeting, repairs may involve patching holes, resoldering seams, or reinforcing the mounting:

1. Take down cap – Carefully remove the damaged custom cap from the chimney. Inspect the sheeting for problem areas.

2. Repair holes – Use same gauge metal sheeting to cut patches covering any holes in the cap. Affix patches with solder (copper) or pop rivets (stainless steel).

3. Resolder seams – For copper caps, resolder any separated seams using lead-free flux and solder. Heat with a torch and flow solder into seam.

4. Resecure loose sheeting – Check all corners and seams for secure sheet metal connections. Refasten loose sheeting with pop rivets or additional solder as needed.

5. Add reinforcement patches – Apply any metal bracing or reinforcement patches on weak or damaged areas using metal sheets and mechanical fasteners.

6. Seal gaps/seams – Seal all seams, joints, and flashing areas with high-temp silicone caulk. Also check crown mounting edge.

7. Remount cap – Before reinstalling the custom cap, inspect the mounting structure. Add reinforcements if needed. Seal and remount using mechanical anchors.

These techniques for patching holes, sealing seams, and reinforcing brackets will repair and strengthen a custom chimney cap.

When to Call a Professional for Chimney Cap Repair

While many chimney cap repairs can be DIY projects, there are some situations when it’s best to call a professional chimney repair contractor:

– Cap damage is extensive or rebuilding is needed
– The cap has shifted and no longer fits chimney crown
– Chimney top or crown also needs rebuilding
– Masonry repairs needed above the roof line
– New custom copper or stainless steel cap is needed
– Special equipment like boom lifts required for roof access
– Severe rusting or deterioration of metal flashings
– Major repairs needed to anchor brackets or mounting bolts
– Unsafe to access deteriorated chimney without scaffolding
– Not sure of the proper repair techniques or materials

Chimney caps protect the interior chimney structure so major repairs should not be tackled as DIY projects. Professional chimney contractors have the skills, equipment, and experience to properly diagnose issues and rebuild or replace severely damaged chimney caps using the right techniques and materials to prevent future problems.

Conclusion

Repairing a damaged chimney cap promptly is crucial to prevent further deterioration of the chimney system. The right materials and repair techniques depends on the cap style, extent of damage, and access to the chimney. Masonry caps require rebuilding using concrete and mortar while prefab metal caps can be patched and resealed. Custom copper and stainless steel caps involve techniques like patching holes, resoldering, and reinforcing brackets. While minor repairs can be DIY projects, it’s often wise to enlist a professional chimney repair contractor if there is extensive damage or safety issues with roof access. With the proper chimney cap repairs, you can restore full function and prevent costly damage from water leaks or animals. Regularly inspect your chimney cap and keep it well maintained.