Fluid-Applied Air Barrier Installation Guide – Commercial Builds

An installation job is the future measuring stick for quality and durability in a structure. Why not get it right the first time?

Air and vapor barriers are essential materials in just about any type of commercial construction. A successfully placed air barrier controls the atmosphere inside the building envelope. It’s one of the last lines of defense against energy loss, low air quality, and moisture intrusion. 

Liquid-applied products are growing in popularity thanks to their adaptability and toughness. However, applying them is trickier than sheet barriers – don’t head to the job site without this checklist for fluid-applied air barrier installation on:

• Exterior walls
• Roofs
• Other transitions between conditioned & unconditioned spaces

How to Install Fluid-Applied Air Barriers: 9-Step Process

The installation process for both air and vapor barriers varies slightly depending on the specific product. That said, the fundamental principles remain the same from one air barrier to another:

1. Get the right tools/equipment
2. Check your surroundings – before and during installation
3. Make sure the right people will be on-site
4. Prep the surface and/or sheathing
5. Measure
6. Flash penetrations
7. Flash rough openings
8. Apply barrier
9. Inspect & repair

(Related Post: How to Install Foam Expansion Joints)

STEP #1: Get the right tools and equipment.

For starters: Are you sure you need a vapor barrier vs. an air or weather barrier?

If you’ve got those basics down long ago, you can move on to checking your tool and equipment kits.

We're all human and don't always remember everything – this chart will make it easy for you:

STEP #2: Check your surroundings – before and during installation.

Before starting the installation of your air barrier, ensure the environment will be conducive to the material you're using. Apply this advice to both the lead-up phase and the actual time of application.

In the days leading up to installation, find acceptable storage conditions for your air barrier materials. Liquid-applied products are prone to damage from:

• Moisture
• Extreme temperatures
• Direct sunlight

Even on installation day, you shouldn’t drag the products out first thing in the morning and leave them exposed to the elements for several hours. Cover ’em up.

When the time to get to work is near, check the site climate’s:

• Temperature
• Humidity
• Dew point
• Surface dampness 

If the temperature is too low or the humidity is too high, the product can flake away and form holes. When using a fluid-applied system, wait until the working surface is completely dry and the dew point is sufficiently low. Yes, this can mean waiting a bit after rain or a drop in humidity – installing over a damp surface can prevent proper adhesion and curing.

All products come with manufacturer guidelines for optimal installation conditions. Your supplier can also answer any concerns, and even get the manufacturer’s rep involved for project-specific installation questions.

STEP #3: Make sure the right people will be on-site.

Installing a fluid-applied air barrier is both a skill- and labor-intensive task. The job includes:

• Surface prep
• Ensuring pumps (where applicable) are ready and gun tips are the right size
• Measuring applied thickness
• Installing
• Sealing
• Covering

Plan to have a sufficient amount of knowledgeable and experienced personnel ready. If your distributor has technical product expertise, it may agree to be on hand and ensure proper use. This team will handle everything from measuring and mixing to the actual installation and timing of each step.  If you’re new to using the product, ask your supplier or manufacturer’s rep to be on-site with you to guide preparation, mixing, and installation.

There’s also a timing factor to installation. Particularly with fluid-applied barriers, the moments between application layers are critical. 

Say you get the first priming coat down with no issues. That’s swell, but if you wait too long (or short) to apply subsequent layers, the product might not adhere or work properly. If you delay long enough, the installation can outright fail, resulting in an expensive do-over.

STEP #4: Prep the surface and/or sheathing.

This is the big one. If you get this step correct, installation will be exponentially easier.

You’ll need to prepare any masonry or concrete surfaces per manufacturer guidelines. Clean, dry, and free the surface of any debris or loose particles. Contaminants to watch for include:

• Dust & dirt
• Oil & grease
• Wax & soap
• Paint & stains
• Concrete coats & sealers
• Anything else that could hurt performance

Stick to mechanical methods of removal. Smooth out surface irregularities need to be smoothed out to avoid compromising the barrier's integrity.

Now’s also the time to seal sheathing joints. This involves applying a sealant or tape to the joints and edges of the sheathing panels to ensure a continuous, airtight surface. If you do it correctly, you’ll prevent air leaks and provide a smooth substrate for adhering a liquid-applied barrier.

STEP #5: Measure.

Calculate the coverage area to find the amount of product you’ll need. This includes walls, floors, and any other surfaces that need protection. Each product comes with a manufacturer-specified coverage rate, usually expressed in square feet per gallon. 

Make sure you have enough to apply it evenly across the surfaces without wasting a bunch of material. Over- or under-application can also affect the barrier’s performance.

Some products require multiple coats, so account for this in your calculations. In areas where barrier sections might overlap (i.e. corners and edges), you may need to apply additional material to ensure full coverage.

STEP #6: Flash the seams and penetrations.

Proper sealing at this stage keeps the integrity of the air barrier intact. You’ll mainly be looking at seams and penetrations as potential trouble sites.

• Seams/gaps: Use manufacturer-recommended tape or sealants to overlap and seal all seams. Apply extra material along seams where two wet areas meet, ensuring a continuous membrane.
  
  
• Penetrations: Add protection in any spots where pipes, ducts, or electrical boxes go through the barrier. Use sealants or gaskets that are compatible with the barrier material to create an airtight and watertight seal.

STEP #7: Flash the rough openings.

Openings in the building envelope – such as windows, doors, and vent spaces – require careful attention.

Use flexible sealants to fill gaps around all openings. The sealant should be material-compatible with both the barrier and the opening’s surface.

(Pro Tip: To evenly fill larger gaps, consider adding backer rods before applying the sealant.)

Ensure that the sealant bonds well with both the air barrier material and surrounding elements like frames or sheathing. The resulting shield should be continuous, with no gaps or thin spots.

STEP #8: Apply the barrier.

It’s finally time to spray, roll, or brush the air barrier onto the surface. Have your manufacturer guidelines at the ready.

Securing the product to the structure shouldn’t be too tough since there’s no mechanical attachment necessary. A qualified installer can apply it directly to the surface in impressively short order.

Ensure complete coverage by applying the barrier uniformly, whether with a strategic painting pattern or by keeping consistent nozzle pressure. Slight overlap is OK, especially at edges and corners. Use a wet film thickness gauge if you want to check application thickness.

STEP #9: Inspect and repair the work as necessary.

You weren’t planning to just walk away now, right? After the installation, conduct a thorough inspection of the air barrier.

Check for any tears, gaps, or improperly sealed areas. Use the appropriate materials to make repairs immediately.

Note the emphasis on “immediately” – swift action is the best way to maintain the barrier’s effectiveness. Regular inspections during construction and after any significant repairs to the building envelope will improve the odds of a long useful life.

More Air/Vapor Barrier Installation & Product Support

Proper installation of air and vapor barriers is not just about preventing annoying water nuisances – it also serves as a measure of the quality and durability of the building.

Once you know how to install an air barrier correctly, you can build a rep as a contractor who puts durability and safety first.

Need more help identifying an ideal product or applying it to a certain job site? Look at our Services page for details on technical training options: