Whatever name you use, caulk simply fills gaps and seals against water and air infiltration. In order for caulk to work properly, it is important to choose the correct caulk for the job.
Types of Caulk
Each type of caulk is suited to a particular material and application. Silicone is compatible with glass but is not good with wood. Asphalt-based sealant is good for roofing materials, but breaks down when used with copper. Copper is a common flashing material for roofs because it can be fabricated into rigid, continuous shapes. It is an expensive material, and using the wrong sealant can damage the material and cause the installation to fail.
Best Sealant for Copper
The Copper Development Association (CDA) publishes an Architectural Design Handbook: Flashings and Copings. It specifies an "elastomeric polyurethane, polysulfide, butyl or silicone rubber sealant" for copper.
To choose which one, consider how the joint is going to expand and how flexible the sealant needs to be. Caulk is not recommended for gaps more than a 1/2 inch wide. Butyl sealants are more flexible than silicone, according to Consumer Reports. Silicone is not compatible with wood or masonry. Remember, asphalt caulk breaks down when used with copper so beware of butyl sealants containing asphalt.
Final Analysis
The Architecture Design Handbook: Flashing and Coping suggests choosing a sealant tested by the manufacturer for use on copper. It is important to read labels and adhere to the specifications and instructions. Copper is one of the most durable materials that can be used for flashing when properly installed. Choosing the best caulk insures you will enjoy your roof longer than it takes it to age to a green patina.
The Drip Cap
- In construction, caulk is rarely celebrated.
- It's a multi-use substance that can waterproof, weatherproof, seal cracks and fill in joints both inside and outside a structure.
- Each type of caulk is suited to a particular material and application.
- Silicone is compatible with glass but is not good with wood.
- Asphalt-based sealant is good for roofing materials, but breaks down when used with copper.