A chimney cap is an essential accessory that keeps the chimney clean and keeps animals and debris out. Though some chimney caps can be secured with screws alone, some are secured with construction adhesives and sealants. Liquid adhesives provide security and waterproof sealing, but they are not necessary on all types of caps. The best adhesive for your installation depends on the type of chimney cap you are installing. It's also important to review manufacturer specifications before securing the cap.
Heavy-duty, waterproof building adhesive composed of polyurethane is ideal for chimney caps. It has a high level of bonding strength and will adequately seal and secure most chimney caps. Building adhesive is usually used for stone, metal and other heavy materials. It can create a watertight seal around the chimney cap. It can also seal roof flashing and repair cracks in the top section of the chimney. Many polyurethane adhesives allow some amount of flexibility, which ensures the adhesive retains its bonding strength.
A silicone sealant is another bonding option for your chimney cap. It provides a high level of waterproofing strength, which will help keep a masonry chimney in optimal condition. Silicon sealants are also used to seal roof flashing and cracks throughout the chimney. Use the sealant to cover the joint where the cap and flue meet. If you are working with a metal flue and a chimney cap that mounts on the inside, you should avoid silicone sealant. The heat conducted by the metal chimney can damage the strength of the silicone.
A chimney cap must be of a size and shape that fits the flue. Chimney caps must be slid over the chimney or into the flue. Inside mount chimneys often come with sealant to secure them in place. Outside mount models may come with metal screws for installation. Top-mount chimney caps are mounted on the chimney crown, and can be installed with screws or sealant depending on what the manufacturer advises. You may need to bend the flanges and spread sealant around the bottom edges to secure a top-mount cap.
A bottle of polyurethane builder's adhesive or silicone sealant is a useful product for chimney maintenance. These products can seal cracks and fix deteriorating sections in brick, concrete and other tough materials. Use them to repair flashing leaks, chimney cracks and cracks in the caulking in all of these areas. The adhesive can also be used to seal open joints.