Sonneborn Joint Expansion Sealants for Concrete Applications

The system is made of soft lead, which has a low elastic modulus. This allows it to remain flexible and slowly 'creep' into new configurations as the building settles or moves. This prevents the cap from tearing and ensures the sealant underneath remains protected from stress and exposure.

It is ideal for protecting horizontal and vertical masonry joints in both new construction and historic restoration. Common applications include copings, parapets, cornices, belt courses, window and door lintels, sills, and entrance steps. It is particularly valued in preserving landmark structures.

Yes, the lead cap can be painted to match the surrounding masonry or architectural details. If left unpainted, its surface will naturally oxidize to a neutral grey color that blends well with most stone and masonry, making it aesthetically versatile for restoration and preservation projects.

We offer a range of stock sizes for both Type A (flat) and Type B (cove) caps to fit joint widths from under 3/8 inch to 1 1/2 inches. All stock items are supplied in 6-foot lengths. Custom sizes and configurations can also be manufactured upon request for unique project requirements.

Absolutely. While widely used in historic preservation, the system is an excellent choice for new construction to ensure long-term joint durability. It provides a robust, weatherproof seal from day one, protecting the structure and minimizing future maintenance needs for exterior sealant joints.

Selection depends on joint geometry. Use Type A (flat cap) for joints between masonry units on the same plane, such as coping top joints. Use Type B (90° cove cap) for right-angle joints, like where a window sill meets a wall. Our technical team can assist with sizing and selection for your specific application.