Underbody Coating

Underbody coating and its purpose.

What is undercoating?

Undercoating or underseal is a thick resilient coating applied to the underbody or chassis of an automobile to protect against impact damage from small stones, which would rapidly chip ordinary paint, allowing rusting to begin.

Historically a bitumen-based compound was used, but after approximately a decade this becomes brittle and water can become trapped between the underseal and body metal, counterproductively creating a more favorable environment for rust than if no underseal was applied at all. wax-based underseals do not have this disadvantage but can be eroded and eventually washed off by the enthusiastic use of hot pressure water. rubber-based underseals are also sometimes used.

BENEFITS OF UNDERCAOTING

• Save money: It’s expensive to have your car undercoated by a professional since it can cost hundreds of dollars for one session. Moreover, you would also have to wait for a couple of days before the job is done. Instead of spending a fortune on an undercoating service, buy a quick-dry undercoat and do the job yourself.
• Reduce road noise: A vehicle’s undercarriage gets noisier as time goes by due to rust and wear. Most undercoats are formulated to seal all the nooks and crannies on the undercarriage that typically lead to road noise.
• Add an extra layer of protection: An undercoat typically acts as an additional layer of protection from mold, moisture, dust, and rot. It also protects your vehicle from dents, scratches, and paint chips.

TYPES OF UNDERCOATING

• RUBBERIZED UNDERCOATING

Rubberized undercoating is easy to apply, and generally offers the best protective coating for your car’s undercarriage. It cushions surfaces against moisture, rust, dings, and dents. Rubberized undercoating is safe to use on quarter panels and wheel wells and dries with a soft rubbery finish.

• ASPHALT-BASED UNDERCOATING

Asphalt-based undercoating offers a higher level of protection suitable for large trucks, recreational vehicles, and heavy machinery. It’s formulated with some bits of rubberized material to aid in noise reduction. It offers extra protection against chips and moisture but is not paintable and, therefore, only suitable for undercarriages.

• POLYURETHANE UNDERCOATING

Polyurethane coating is easy to apply and works by sealing up cracks and seams. The compound displaces salt and moisture and protects the unoxidized metal from rust. It’s often sold in canisters that are ready to preload into an application gun. It, however, requires some surface prep work before application, like degreasing, and applying an etching primer to the bare metal.

• WAX OR PARAFFIN-BASED UNDERCOATING

Wax or paraffin-based undercoating sprays are the cheapest and quickest options available. However, their results don’t last long, and you may have to apply a fresh coat after only a few months. In addition, the wax isn’t very adhesive on a metal surface. Its main advantage is that it seeps quickly into cracks and seams, and offers moderate protective properties against moisture.

UNDERCOATING PROCESS :

Modern automotive coating methods consist of five main steps. They include the following:

• Pretreatment: removes and cleans excess metal and forms an appropriate surface structure enabling bonding of a corrosion protection layer.
• The next step is electrodeposition (ED) of the anti-corrosion or rust prevention layer.
• A sealer like Poly Vinyl Chloride (PVC) is applied for anti-corrosion, elimination of water leaks, and minimization of chipping and vibrational noise.
• A primer is then applied to promote adhesion between the surface and the basecoat; it also imparts a smoother surface for subsequent layers and has anti-chipping properties.
• Finally, the topcoats that include a basecoat and clearcoat are applied; they provide surface properties that are sought after, including color, appearance, gloss, smoothness, and weather resistance.

• Pretreatment

When the automobile body sheet metal components are welded together, the resulting structure is referred to as the body-in-white (BIW). The first sequence in preparing the BIW for subsequent coating is pretreatment. Pretreatment consists of cleaning the body surface to remove remaining oils from the stamping process and welding residues through three primary liquid dip processes of degreasing, conditioning, and phosphating.

• Electrodeposition (ED)

The metal underbody and frames of automobiles are coated to prevent corrosion, whereas other areas like the roof are not rust-proofed. When not coated to prevent corrosion, the structural metals (or other materials) are primed before applying additional coatings. The electrodeposition coat or E-coat provides rust and corrosion protection and was first introduced in the 1960s. Since then the use of E-coat has grown at a rapid pace

• Rust-Proof Materials: Sealer/PVC

The third step is underbody coating (UBC) and seam sealing using PVC (Polyvinyl Chloride) and urethane. This sealing has multiple purposes. The sealant is applied around and inside the doors, hood, trunk, and front dash, and onto the exterior and interior of metal joints and outer area of the back wheel well; application of the sealant is accomplished either manually or with robots and prevents air and water ingress and inhibits rust formation. During this third step, it is also typical to apply a soft tip primer coat that improves the chipping resistance (resistance against chipping by flying stones or debris)

• Primer

The fourth coating step is the application of a primer surfacer or simply primer. It can be water-borne, solvent-borne, or a powder. The main reason for primer application until 1990 was to improve weather resistance, appearance, and chipping resistance. Since 1990, primers have been developed in solvent-borne and water-borne materials, and powders (explicitly for reducing the amount of volatile organic compounds (VOC) discharged into the atmosphere or pollutant capture equipment). The primer fills and smooths minor imperfections and scratches that may be created during prior steps and by the intermediate sanding or grinding used to remove small imperfections. Additionally, most automobile bodies have surface imperfections that arise from the pressing, stamping, and welding operations, and these defects are typically accentuated during the ED step. Hence, although the main purpose of the primer has been to act as a leveler that produces a smoother finished surface

• Topcoat

The final step in the body coating process is to apply the top coat, which consists of two layers—the basecoat and clearcoat. The basecoat contains the primary coloring pigment, and the clear coat provides a protective coating against environmental effects, corrosion, and UV light degradation, promotes unmatched color retention, and provides a smooth, unblemished, and even finish. The body is first coated with either a water-borne or solvent-borne basecoat. If the manufacturer is using a wet-on-wet process, then the clear coat is applied onto the base coat after a short flash-off, before curing in an oven. In the absence of a wet-on-wet process, the base coat is cured before the clear coat is applied.