Seam sealers grow in acceptance - not only as a solid repair solution, but also for their NVH characteristics.

Today’s vehicles are becoming more complex every year. Fortunately, automobiles are being manufactured to higher quality standards than ever before. As a result, the use of sealers and sound-deadening agents in vehicle design and production has increased considerably. In fact, it is estimated that seam sealer products account for nearly 50% of the aftermarket adhesive used in automotive collision repair. Found nearly everywhere there is a hem or joining of metal, seam sealers are the most prevalent adhesive application used on vehicles today. Though seam-sealer applications are an everyday operation in body shops, with a well-known ability to provide a reliable seal, today’s seam sealers are also gaining favor as an accepted means to combat all types of noise, vibration and harshness (NVH) issues. Further, carmakers can use lighter, stronger metals in conjunction with sealer technology to make passenger vehicles more fuel efficient, safe and quiet at the same time.

According to Gerry Bonanni, Ford Body, Paint Damageability engineer, liquid seam-sealing products are being used more frequently in automobile manufacturing to cut down on NVH and reduce weight.  “These sealer products are easier to apply during the production process and are less costly than traditional mastic pads,” said Bonanni.

General Seam Sealing

Typically applied to seams at quarter panels, roof panels, hoods, deck lids, door skins, rear body panels, frame rails, rocker panels, floor pans, pillars and aprons, today’s seam sealers are available in multiple chemical varieties. Offered as 1K or 2K products, seam sealers are typically composed of urethane, epoxy, rubber/solvent-based or MS polymer. Further, sealers can be specified by application, such as factory match, controlled flow, self-leveling, sound deadening, sprayable or wind/water leak repair. And, the use of these products to reduce noise is simply skyrocketing. Wheelhouse areas, fender aprons, cowl areas and floors are locations where large amounts of sound-deadening sealer-type material are now being found. Some manufacturers are using these products on the backsides of door panels, quarter panels and fenders to keep noise out.

The key to selecting the correct seam sealer is knowing the specified application as well as the desired work time and full cure time. Although a factory match seam sealer can be used to duplicate most factory seams with creative tooling, several working and cure times are available, making selection tricky. For example, catalyzed 2K sealers have accelerated working/cure times that can set up quickly in five to 15 minutes and are typically paintable in 10 to 30 minutes. These types of sealer products are popular when replacing door skins, quarter panels and rear body panels, and work well for technicians who want fast performance. In comparison, though the 1K factory match sealers take up to an hour to set (full cure in about 72 hours), these products are typically less expensive and are paintable in about 10 minutes.

When performing basic seam sealing, the technician should be careful to choose the right product for the job and follow the recommended instructions. For example, a rush door skin job would probably be a good candidate for a fast-cure 2K seam sealer, as a 1K may be too slow in curing to allow for quick door reassembly and vehicle delivery without inflicting possible damage to the still-uncured sealer underneath the freshly coated paint. A review of common types of sealers and their attributes follows.

Self-Leveling Sealers

A good solution for sloped surfaces, roof channels, drip rails and truck bed floor seams is a controlled flow seam sealer. These types of products are semi-self leveling and have built-in sag characteristics. These attributes naturally eliminate bead appearance imperfections and allow for a dispensed bead boasting a rounded “half-moon” look.  In addition, the controlled flow formula enables technicians to make a smooth bead without tooling, has a fast working/cure time and gives the body technician the ability to sand to a professional featheredge after 30 minutes of adhesive application.

Although self-leveling seam sealers are a relatively new technology, they are already being widely used as a solution for the latest vehicles. While used mostly on roof ditch areas, other uses include core supports to aprons, trunk seams and quarter panels to roof deck areas. The sealer levels itself within its applied area, can be brushed and does not usually require any further tooling. In most cases, this type of product sets up fast and can be painted within 30 minutes. For best results, self-leveling seam sealers should be applied exactly as directed by the manufacturer, as these types of flexible products require the use of flex agents within the paint system during refinishing.

Sprayable Seam Sealers and Sound Deadening

Sprayable sealers are definitely growing in popularity and are commonly used to spray textured trunk floors and wheelhouse areas. They also work well as a stone guard coating for rocker panels and lower portions of exterior body skins. The stone guard can then be painted over immediately with a preferred basecoat/clearcoat system. With atomized pneumatic spray guns, the technician can control the thickness and texture of the dispensed product. Sprayable seam sealers also can be used to lay traditional beads if necessary, and are an excellent option for duplicating robotic-applied factory floor seams.

When thinking about replacing factory sound-deadening materials, sprayable sealer products are often an excellent choice. These sprayable products offer the technician versatility to bring vehicles back to pre-loss condition. For example, “Q-pads” are considered the traditional method for replacing damaged OEM sound-deadening materials in trunk floor areas. However, most technicians will agree that “Q-pads” do not provide the desired appearance, as they often look sloppy after being applied.  With a little masking, pneumatically applied, sprayable sound-deadening sealers allow the body technician to apply uniform product to the floor panel at the desired thickness and texture. Newer cars are utilizing sound-deadening products in large volumes underneath carpet in the passenger compartment floor areas. These areas also can be restored to factory specifications with little effort. The end result is a quality, invisible repair that technicians and customers can certainly be proud of.

Tooling Tips

Although the use of robots on the assembly line helps auto makers build vehicles to precise standards, seam sealers are still manually applied by people in most cases. As mentioned before, seam sealers are found everywhere on the car body, and with a little practice, the factory seams can be matched successfully. When duplicating brushed seams, a full bodied, non-sag product works best. The technician should apply ¾-inch masking tape along both sides of the joint and apply an ample amount of sealer to allow for brushing and spreading. Then, the technician can either use a stiff 1-inch paintbrush or a red scuff pad to drag along the sealer in one direction. Simply remove the tape to reveal a beautiful brushed seam that boasts the OEM look. If wet tooling is desired, water can typically be safely utilized. On flat beads, the use of masking tape, seam sealer, a plastic spreader and a steady hand work extremely well to obtain the desired form.

When applying self-leveling materials, air bubbles sometimes become evident throughout the seam. These can typically be avoided beforehand with proper product purging; however, when bubbles develop after dispensing, they can easily be removed by using a sharp pick or a razor blade tip to pop them.

Smooth, rounded beads are often found on hoods, doors, deck lids and truck bed floors. Most body technicians find these extremely difficult to duplicate, but these seams can be matched with the use of controlled flow materials. As with brushed beads, masking tape works well to make an attractive bead. Simply apply tape to both sides of the seam, apply enough controlled flow product to slightly extend onto both pieces of tape and then pull the tape straight back.  This usually fixes any flaws in the bead and provides a smooth, rounded look.

Seam Sealer Success

Working with seam sealers and making them look nice has become easier than ever before.  Adhesive manufacturers understand the needs of body professionals and produce products that perform as advertised and provide a factory look. Ask your supplier about the specific sealer products available, and be sure to read the product technical sheets for application suggestions and cure times. The sealer/adhesive manufacturer is another excellent source for help, and many of them have phone or web-based technical support. With some quick practice, technicians can confidently apply seam sealers just like the OEMs do.

Bob Zweng is the Senior Technical Service Representative for LORD Corp., maker of LORD Fusor® Automotive Repair Adhesives. Zweng is I-CAR trained and ASE Master Certified.  He can be reached at (800) 234- FUSOR, ext. 2, or e-mail

For more information, phone 800-659-5805 ext. 617 or visit