The series covers when technicians may still want to prime when using DTM products to prevent corrosion and when they can forge ahead and apply directly to the metal. Repairers will understand what DTM products are and how to use them properly to perform the “perfect repair.” Part two explains procedures and differences.
Seam sealers are used for duplicating factory appearance during automobile repair and industrial heavy-duty truck, bus and trailer repair. Currently, there are two seam sealer processes in use in the industry. Repair shops can use Direct-to-Metal (DTM) seam sealers or a two-component primer followed by a seam sealer. DTM seam sealers, as the name implies, are applied directly to the metal surface without the use of a primer beforehand. There are some questions within the industry as to which method to use. Many repair shops follow the two-component primer method as it does provide a better repair. Since a primer is not necessary for DTM sealers, they are often used when highest corrosion protection is not needed. Although each automobile manufacturer offers its own recommendations, in the end it is up to the individual shop as to which process to use.
One-component vs. two-component seam sealers
As the names imply, a one-component sealer uses only one material. A one-component system uses a caulking gun to apply the product onto the car where it begins to cure. Most one-component sealers cure via a reaction with water in the air. A two-component seam sealer involves the mixing of two different materials to create the sealer. The two-component system utilizes a cartridge system that contains two parts - A and B. As it’s being extruded, it will go through the mixer to combine the parts. When it reaches the car, it is mixed and is now having a chemical reaction that will activate curing.
Curing
The one-component sealer material begins to cure based on shop temperature and humidity level. With one-component products their cure time can be affected by the weather. During the summer, humidity levels tend to be high which provides the moisture needed to cure. In the fall, the temperatures start to change and get cooler, and humidity levels lower which leads to slower curing. Different geographic areas will have different cure times as well, such as the Southwest, which tends to be dryer. The seasonal differences in humidity changes curing speed and often causes an influx of phone calls to the material’s manufacturer about the product not curing. It’s curing, just significantly slower. Every product has a different cure time for a certain temperature, so it’s important to be familiar with the product being used and how much time it needs.
To move a repair through the shop faster when temperatures are a concern, the two-component products are superior. They will go through a chemical cure due to mixing A and B together. As long as it's not too cold, these sealers cure rather quickly and do not rely on outside humidity for the chemical reaction to occur. The one-component products are generally firm in 25-30 minutes and cure in roughly 24 hours, depending how thick it is. So, it could be a longer time with certain weather conditions.
A two-component sealer can cure faster since it doesn’t rely on the absorption of moisture. How fast the sealer cures will depend upon the formula. Generally, they are firm in 3 to 20 minutes – much faster than one-component sealers.
After a half-hour most every seam sealer is firm enough that you can’t make a mark on it. While it may not fully cure for 24 to 48 hours, you can touch it without damaging it and with most the paint can be applied to it.
To keep the repairs moving in the shop, paint can be applied and dry while the seam sealer is hardening. With some seam sealers paint can be applied immediately, with others you may need to wait 10 to 30 minutes - but this isn’t a long time. After the parts are seam sealed, they will typically be moved to the paint area, which takes time.
It’s important to know your seam sealer and its bond and cure times. Complaints arise when the masking pulls paint off the seam sealer. That’s because the whole system has not cured, and the bond has not fully developed. This occurs most commonly with one-component materials.
Two-component seam sealers, because they're chemically curing, are generally fully cured in 24 hours but are firm to the touch, and paintable in minutes depending upon the formula used and the shop temperature. Even though they may not be fully cured, the early bond strength of the paint system is generally superior to one-component materials.
Don’t forget that the seam sealing products you’re using, and your paint system, need to be tested on a scrap panel so you know clearly how your systems work together. It’s important to test the paint on the seam sealer to ensure you will get the results you want.
Process
· Sand any paint edges before the seam sealer goes down so you’re not working around fresh sealer when prepping for paint.
· Clean! Make sure there is no dust, dirt or rust on the shiny metal.
· Apply masking tape, if desired, to define the size of finished bead.
Procedure for one-component seam sealer
· Place into caulking gun and prepare per manufacturer’s directions.
· Apply sealer.
· Sealer can be spread with a spreader.
· Sealer can be brushed for a brushed appearance.
Steps for two-component seam sealer
· Prepare the seam sealer cartridge ahead of use.
· The first step in preparation is leveling by placing the cartridge in the applicator gun and extruding until you see the material. This is an important step. There could be a couple millimeters more of material on one side, so leveling ensures both A and B side come out on ratio.
· The next step is, when ready to apply the seam sealer, extrude a mixer’s length sealer as waste ensuring that A and B are mixing properly. If striations or streaks are visible, the mix is not even. Extrude more material until it is evenly mixed.
· Leveling and purging errors are where almost all product failures begin.
· Apply sealer.
· Seam sealer can be spread with a spreader.
· Seam sealer can be brushed for a brushed appearance.
Types of seam sealers
· Non-Sag: Thick and holds texture such as brush marks.
· Controlled Flow: Thinner in viscosity. They are still thick but will smooth out when tape is removed.
· Self-Leveling: Very thin and will flow out to an edge. One use is where the side of car meets roof.
Avoid usage errors
When choosing a seam sealer to use, consider the how much time you need and if your surrounding temperature will affect your cure time. Most importantly, always remember to level and purge before using any two-component system. Omitting the leveling and purging steps result in most of the application problems.
Additionally, every product has technical data sheets and a training program to show the proper use. Use these resources to train all technicians in the best procedures. It seems simple, but don’t forget seam sealer manufacturers always have a customer service phone number, website and email for questions. The manufacturer is the most underused resource for a technician.
For questions and more information on seam sealers and the Fusor system, contact Parker LORD at 877-275-5673 or visit Fusor.com.
