Sealants for Building Structures

Building Sealant

Sealants for Building Structures

The function of sealants is to close gaps and joint openings in building structures. The ideal sealant will provide an adequate bond and be flexible enough to tolerate anticipated movement between substrate materials.

Dowsil 795 silicone building sealant is suitable for structural glazing, expansion and control joints, precast concrete panel joints, EIFS joints, and curtainwall joints. It is nonhazardous when cured.

Expansion Joints

Structural expansion joints are gaps designed into buildings to accommodate movement, typically allowing one fourth of the slab thickness to move. These joints must be filled and sealed to ensure watertight integrity. When not properly sealed, these joints can create an area where dirt and debris collect and weeds may grow. This erodes the joint filler material and leads to displacement of concrete. The movement of the slab through these expansion joints can also heave or push up against the foundation, creating major cracks and other building damage.

A variety of sealant solutions are available for these applications, some of which include elastomeric, polyurethane and epoxy. In selecting a product for use in this application, it is important to understand the specific movement capability of each. Look for a joint sealant that Building Sealant has been tested and certified to accommodate the expected movement, in terms of both elongation and compression.

Some expansion joint solutions are available in pre-slit and/or cut lengths to make installation easier and faster. One example is FillPro FBR expansion joint filler, a light gray strip that is easily pulled back and used to form a clean line of sealant in the gap. This closed-cell foam won’t swell or absorb moisture that could freeze in winter and follows curves well, making it a convenient option for this type of project.

Window & Door Perimeters

Many older window frames and doors are damaged or worn and no longer do their job. The wear and tear of time can cause them to let air and water into the building. To prevent this, windows and doors should be properly sealed when installed.

A strip of self-stick plastic (vinyl is most popular) or springy bronze strip shaped to bridge a gap and block drafts. It is easy to install, durable and provides a good seal for corners and irregular cracks. Use it on top or bottom of window sash, inside tracks of sliding doors, and at the head jamb in double-hung windows. This product is available as a replacement for and generally outperforms liquid caulk and butyl tape.

For strengthening the installation of a window in a frame wall: Screws have to be long enough to penetrate the framing of the house, the shim space and a wood buck strip (if needed) plus get a bite into the masonry wall. Be sure to pre-drill a hole for each screw and use a bevel head.

A colorless and odorless gas used to fill the airspace between Low E glass, which significantly increases its insulating capability.

Floor Joints

Floor joints are created in concrete slabs and screeds to allow natural expansions and structural movements. For this type of joint, it is important that the selected sealant be able to withstand cyclical tension and compression within the joint while maintaining its shape (the so-called “shape factor”), and must be able to adhere to the substrate without degrading due to repeated exposure to moisture.

The choice of joint shape and size is largely determined by the type of loading to be encountered in the building – for instance pedestrian traffic, heavy vehicles and trolleys. For floors subject to frequent loading, a profile with a high modulus of elasticity and a wide range of movement capacity is recommended. Sika offers a variety of profile solutions for this application, from the standard round bars to the more technically advanced structural joints with waterproofing sheath such as Jointec GW and Coflex CR.

Another important consideration for the selection of a building sealant is its ability to withstand moisture, particularly humidity. For this reason, a primer should typically be applied to the joint surface prior to sealant installation (depending on the manufacturer’s recommendations and/or the substrate, the recommended elapsed time between primer and sealant application may vary).

Wall Joints

Wall joints are often prone to water intrusion, such as at window-to-wall connections or at control joints. The right sealant technology is important in these transitions, but ensuring that the substrate surface is sound and capable of adhering to the joint filler material is also crucial. Backup materials such as backer rod or joint filler should be installed to restrict the sealant depth, support the bond, and facilitate tooling. It is common practice to install the backer rod prior to sealant application in order to avoid creating a bond break between the backing and the sealant.

When sealing movement joints such as control or expansion joints, the sealant should be a flexible elastomer designed to accommodate large Building Sealant linear movements. In order to determine the proper movement capability of a sealant, it is recommended that it be tested by a qualified lab.

Most sealant mistakes on construction projects are related to misjudging movement and selecting a product that can’t meet the intended movement capabilities. In order to prevent these errors, it is essential that the scope of sealant work be properly defined and detailed on the drawings. This information can be specified in many ways: by listing manufacturer and brand name(s) or by describing the desired characteristics, often through reference to voluntary standards. In either case, the information should clearly identify all the movement joints to be sealed.

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