Physical Characteristics of Building Sealants

Physical Characteristics of Building Sealants

The physical characteristics of sealants are critical for determining how they will perform in the conditions under which they are installed. This includes movement capabilities (ASTM C719), and recovery properties.

Movement in walls can be caused by seismic movements, elastic frame shortening, live load, and concrete shrinkage. The resulting movement must be evaluated, designed for, and accommodated with the appropriate joint design.

Moisture Resistance

Sealants block the passage of moisture, vapor and gases in construction applications. They may also provide thermal and acoustical insulation, act as fire barriers, or serve to smooth surfaces and fill gaps.

The first and most important property that Building Sealant any sealant must possess is its moisture resistance, and it must be able to withstand the movement, temperatures and sunlight (UV radiation) of the typical building environment. The best indicator of this is the manufacturer’s weathering data with stress induced movements.

A good example of this is AU-1 Commercial Construction Sealant which can be used in all climates and has excellent mold, mildew and fungus resistance. It is self-leveling, paintable and meets all SCAQMD and CARB VOC requirements. Its internal plasticizer bleed is minimal and its crosslinking on a molecular level allows it to bond extremely well to most construction materials.

Many countries now have sustainability rating systems which award credits or points to projects for using environmentally friendly materials and approaches in design, construction and operations and maintenance. The rating system takes into account a number of criteria, including:


The strength of adhesion of the sealant to its substrate is very important. It is a good idea to use primers when applicable (check manufacturer’s instructions) to ensure proper bonding of the substrate to the sealant. This is especially critical for traffic joints and other working joints that will be exposed to movement and the elements.

The type of surface that the sealant will be bonded to is also an important consideration. Some sealants are designed for specific substrates and need to be tested on those types of surfaces in order to verify that they have adequate adhesion. Other manufacturers of sealants produce a variety of products that can be used on many different types of substrates and it is up to the building owner, architect or specifier to understand what each type of sealant is capable of doing and to select a product that will work for the project.

In addition to the typical tests in a lab there are also outdoor studies of the sealant in a weathering facility. The results of this testing can provide some clues as to the longevity of a sealant for a particular project. However, the test data can only be interpreted with the input from the manufacturer of the sealant and it is difficult to make long term predictions.


When sealants are specified or incorporated in construction projects the building owner and architect will often ask the sealant manufacturer to provide test data that indicates how well the sealant can accommodate expected movement. There are several important factors to consider when reviewing this information.

One is the actual cured joint width. This should match the design drawing to prevent stress in the structural sealant joint that results from differential thermal movements. The other factor is the movement capability as tested by ASTM C719. This test method defines a class that indicates how much Building Sealant extension and compression (plus or minus) the sealant can take from its original cured joint width.

Lastly, the test procedures that define how the sealant can handle extended periods of movement are also important. Look at ASTM C1589/C1589M, Section 10.2 Procedure B–Outdoor Weathering of Building Joint Sealants With Continuous Movement or Section 10.3 Procedure C–Outdoor Weathering of Building Joints with Periodic Manual Extension and Compression.

Many other tests are available for specific applications and conditions of use, but the most critical is ensuring that the sealant has been formulated to meet the physical requirements for the job being performed. The specifier, the applicator and the sealant manufacturer must work together to ensure that the product being used is appropriate for its intended uses.


The durability of sealants is an important characteristic to consider. Most sealants need to be able to stand up to the environment in which they will be used. This includes the climate and the movement that they will experience. These movements can be caused by seismic movement, elastic frame shortening, concrete shrinkage and even varying levels of live load. In addition, sealants can be subject to movement during accelerated weathering. This combination of movement with weathering decreases the performance of a sealant significantly.

The ability of sealants to withstand high temperatures is also an important consideration. It is not uncommon for the surfaces of building facades or other areas to be exposed to temperatures in excess of 80degC (176degF). It is important that sealants used in these applications have the capability to withstand these temperatures. Sealant manufacturers should be able to provide data on this.

For many applications, such as expansion and control joints in walls, it is often a good idea to use a backer or flashing material to separate the substrate from the sealant. This can help to prevent the movement of the sealant from causing premature failure of the joint. In addition, the backer can also add some strength to the sealant. This can be very helpful in some of the more difficult to seal locations in buildings.