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Sealant Application Tips

While filling joints with sealants may appear easy, contractors know that the task requires proper preparation and attention to several key details to make the process successful. And this attention is required before the first tube is loaded into the gun. Your White Cap Account Manager is a great technical resource for double-checking order quantity and selecting the sealant that matches the application. Once the material is on hand, the real work begins.

Check the Jobsite Weather Conditions

The starting point for effective sealant installation is creating a worksite in which the sealant will dry and cure properly. Manufacturers recommend that applicators place sealants when the temperature is higher than 40˚F and below 70˚F. When jobsite conditions are in this temperature range, sealants dry to the touch in about 30 minutes and fully cure in about 24 hours. Quick drying is important as it helps ensures a good-looking bead, but proper curing is vital because it provides the durability needed for long-service.

Placing sealants in very hot weather or direct sunlight should be avoided. The sealant’s cure may be accelerated, but at the risk of reducing the installation’s service life.

When application occurs at temperatures lower than 40˚F to 32˚F, the sealant’s cure rate is significantly reduced. The sealant may look dry, but it can also be tacky to the touch. And when temperatures are in this range, final curing could be extended by an additional 24 hours. If you must work in this temperature range, warm the work area to acceptable conditions and try to preheat directly at the application point. Check with your White Cap technical resource to opt for a sealant with accelerated curing times.

Properly Preparing the Application Area

For the sealant to perform effectively over time, joint surfaces must be clean, dry, dust-free and frost-free. It’s best to perform the cleaning and surface prep just before you plan to install the sealant.

For most applications, the two-cloth cleaning method is very effective. First wipe the joint surface with a clean, white, lint-free cloth that is dampened with an approved cleaning agent. Then use a second clean cloth to immediately wipe the solvent from the surface before it flashes off. Continue these steps until the second wipe yields a clean cloth. Before starting the application in earnest, you might want to perform a pull test on a sample surface area to be sure the cleaning method is effective.

Some substrate surfaces might require a few additional preparation steps.
Concrete and masonry surfaces must be fully cured, clean, and dry. Be sure to remove any curing agents and form release products that might still be present. Try to create a smooth surface by sandblasting, wire brushing, or grinding.
Wood surfaces require two considerations. Silicone sealants cannot develop proper adhesion if the wood is oily. Wood oils must be given time to dry before silicone sealants are used. If the surface is painted, check the bond of the paint to the wood. The sealants will be adhering to the paint so if the bond is weak, the sealant may not be effective.
Metal surfaces must be clean, dry, and free from rust.

Priming the Surface Area

A sealant’s effectiveness is determined by its adhesion to the surface to which it is applied. Primers designed for use with sealants will enhance this adhesion. When opting for a sealant primer, you must first determine if the target surface is either porous or non-porous.

Porous surfaces, such as concrete, masonry block, and bricks, generally do not require sealant primers. But there could be job-specific conditions that might require a primer, such as a polished or a ground surface.
Construction Workers on Jobsite Preparing for Sealant Application
Non-porous surfaces on common construction materials, such as glass, metal, or plastics will typically develop adhesion with sealant without primer. Even so, you might want to consider priming the surface. When you apply a primer to the bonding surface, sealants will complete adhesion to the substrate faster than if the surface had been untreated. Manufacturers offer different primers for metal and other non-porous surfaces.

Creating the Right Sealant Geometry with Backing

Creating the right geometry in the joint prior to filling will not only avoid sealant adhesion to the backer rod, but proper backing also helps create a more effective application. Properly positioned backing material (also known as backer rod) will prevent three-sided adhesion, control sealant depth, and allow for better tooling. This combination also helps maintain proper sealant/substrate contact. You know you’ve accomplished this when the final look features an hour-glass sealant bead.

The most common backing is cylindrical foam. The material comes in several diameters. You should select a backer rod that is approximately 25% larger than the width of the joint. This is to ensure a tight compressed fit. When the joints are not deep enough to accept a backer rod, a polyethylene bond breaker tape should be installed. The bond breaker tape stops the sealant from adhering to the surfaces and prevents three-sided adhesion.

It’s important to match the sealant contact depth to the type of joints. The sealant joint depth is measured from the face of the sealant bead to the crown of the backer rod.
Construction Worker Applying Sika Sealant on Curtain Wall

For expansion joints, sealant manufacturers recommend that the contact depth should be equal to one-half the sealant joint width.

For window perimeter joints, such as fillet beads or angle beads around windows and doors, the minimum sealant contact depth should be 1/4" onto each substrate. This will allow the sealant to withstand joint movement.

Structural glazing requires special consideration when determining contact depth. Refer to manufacturer guidelines.

Proper Joint Filling Techniques

Filling a joint requires practice and attention to detail. It’s important not to rely on tooling alone to provide good sealant bonding to the joint surface.

There are two important rules to follow when filling the joint:

1. Joints must be filled from the backside to the frontside. This technique ensures that you don’t entrap air or leave a void between the joint surface and the sealant bead. As you fill, make sure to place a uniform sealant depth. This requires a professional grade cartridge-type caulking gun or bulk loading gun.

2. You must make sure that there is complete contact between the sealant and joint bonding surfaces along the entire depth. You can accomplish this “wetting” of the surface by applying a slight force during gunning. Matching the caulking gun’s nozzle to the joint’s width also aids wetting.

Learn more about proper caulk gun usage here.


The final step in the sealant application process is tooling. Tooling is the process of applying consistent pressure to the sealant body through the exposed face of the sealant bead by running a rounded tip spatula along the exterior surface of the sealant bead. A slightly concave surface on the finished bead is one characteristic of a properly tooled sealant.
Tooling serves three purposes:
1. Tooling the sealant joint will create an installation that has full “wetting” of the sealant onto the joint interfaces. The use of controlled force helps assure the sealant has fully “wetted” the bonding interfaces of the substrates.

2. Proper tooling will produce an hourglass shaped cross-sectional joint geometry that assures proper bed depth. The applicator should apply substantial pressure with the tooling spatula to the face of the sealant bead to ensure the sealant has completely filled into the joint.
Construction Worker Using Spatula to place sealant
3. Tooling leaves the visible surface of the sealant joint with a clean and consistent appearance. The appearance is more than show. It’s important to shape the visible surface so that it sheds water and prevents the ponding of water on the surface of the joint.

As with working with all materials that cure, proper timing of tooling is important. You must tool the sealant before the bead’s surface starts to skin over. If you wait too long, the sealant will start to set by forming a hardened surface. At this point, the sealant isn’t plastic enough to retain the desired shape after the spatula comes in contact.


The Right Combination Makes Sealant Applications Look Easy

The skill and experience of the sealant applicator is a key contributor to a successful sealant application. But it’s important to have the right tools to clean and prep the joint, the right sealant for the type of joint, and a support team that can advise you on those unique sealant jobs.

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