Collection: Guide to Automotive Seam Sealer

Determining which seam sealer you need can be overwhelming. There are different color options, different applications and preparations based on the item that you select. This article is designed to help you determine which seam sealer automotive product you may need and how to use it. So let's start with the basics.

What is Seam Sealer?

Seam Sealer is a material that is used to essentially close and seal gaps between over areas that have been welded or where there is overlap. The purpose of using this material is to prevent rust or corrosion and to a smooth surface that can then be painted.

As we primarily carry 3M seam seal products, we will focus largely on these items in this article.

The products that we focus on in this article are intended for automotive use and these products are not intended for use on other items such as tents. More detailed information on each specific product can be found product pages as well as on product packaging or literature. For example, certain products are labeled as brushable seam sealer or as self leveling seam sealer and should be applied as directed in the intended labeled and packaged.

There is some terminology frequently used to describe these products. We have outlined these terms below:

Flexible vs Semi-Rigid:

• These terms are related to both the thickness of the seam sealer. In addition, it provides some information on the rigidity of the cure

There are essentially two different types of packaging that determine how the sealant is dispersed.

• Dual cartridge packages require the use of applicators (like the 3M Manual Cartridge Applicator) to disperse
• Burrito packages come with nozzles to assist with dispensing.

Self-Leveling products (like 3M 8307) tend to be runny and, as the name suggests, will automatically level. These products function similarly to water. Once the sealer is dispensed, it will flow through the area. For this reason, a border needs to be in place before the product is dispensed.

Brush On seam sealer tends to be thicker and can be manually leveled with tools like spreaders or acid brushes to apply the sealer as desired.

How Long Does Auto Body Seam Sealer Last?

If this process is done correctly, seams can be protected for the life of the vehicle.

Does 3M Seam Sealer Shrink?

We strongly recommend looking closely at the package instructions for each product to confirm how much shrinkage should be expected as this may vary.

Most 3M products are designed for minimal shrinkage.

Preparation and Application:

Prepping an area prior to applying these products is essential for a clean finish. It is not recommended to apply these products directly on bare metal and painted surfaces unless otherwise specified on the applicable product packaging. It is ideal to apply these items to primed metal.

• Appropriately mask the area
• If you are using a self leveling seam sealer, make sure that a border has been created.
• Ensure the surface is smoothed to a featheredge. When you run your finger over the surface, you should not feel different layers of paint. 3M recommends Scotch Brite Hand Pads 7447 or Durable Flex Hand Pads for this step.
• Clean the surface with a clean cloth or paper towel. You may use degreaser or an all purpose cleaner, but ensure that you have not saturated the area. Saturation of the area may result in an unsuccessful seam.
• Apply Tight Coat 
• Apply Seam Sealer - Please see the section above regarding self leveling and brushable seam sealer for more details on how to complete this step.
• Allow the product to dry sufficiently.
• Dry time may be as quick as 30-45 minutes. It may even be hard enough in this time that you are no longer able to make brush marks.
• Curing time also varies significantly. Some 3M products dry and cure as quickly as 15 minutes and can be painted immediately after that.

Seam Sealer Tape:

Seam sealing tape may be used in some instances to duplicate the look of liquid seam sealers. We offer options in 3/8 inch and 7/8 inch sizes to be used in areas like door jambs and trunk gutters. These do not require shaping or any dry time and can be painted immediately!

Once paint is applied, the solvent in the paint activates the adhesive in this seam tape.

Sound Deadening Pads:

Sound Deadening Pads reduce road noise, sound system vibrations and other noises that can be distracting to drivers. Seam Sealer can be used to adhere these pads to the trunks, door panels, floor pans, hoods and other areas for a better driver experience.

3M Adhesive products can also be found on this page.

Most recently updated on April 30, 2022.