Underbody Coating

Underbody Coating

Underbody Coating is a sprayable coating, which protects the under surface of the vehicle from corrosion.

Underbody coating provides long term protection from corrosion to car's underbody. It also protects parts like internal body panels, frame rails and other inner cavities that are not physically accessible but are prone to corrosion.

Protecting the underbelly of the car should be our top priority. Especially during monsoon when heavy precipitation causes the roads to become mini-rivers and our cars are left stranded there. This makes them prone to heavy corrosion in the underbody region.

Automotive coating process

• Pre-treatment:

The first step in preparing BIW for subsequent coating is the pre-treatment process. Pre-treatment 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. The degreasing solution is composed of alkaline salts and surfactants and can include caustic soda, tri-sodium phosphate, and sodium carbonate. The surfactants are types of detergents for emulsifying oils and lubricants on the BIW.

• 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 ED processes are modified as per the BIW material property. This ED coating provides rust and corrosion protection.

• Rust-proof materials: Sealer/PVC

The third step is underbody coating (UBC) and seam sealing using PVC and urethane. 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.

• Primer:

The fourth coating step is the application of a primer surface or simply primer. It can be water-borne, solvent-borne or a powder. These primers are used to improve adhesion between the E-coat and topcoat, provide chipping protection, enhance paint appearance and also be environmentally compatible with emission regulations.

• Top-coat:

The final step in the body coating process is to apply the topcoat, which consists of two layers—the basecoat and clear coat. The basecoat contains the primary colouring pigment and the clear coat provides a protective coating against environmental effects, corrosion, and UV light degradation promotes unmatched colour retention and provides a smooth unblemished even finish.

A protective coating composition for motor-vehicle underbodies and gravel guards, characterised in that it comprises, in percentages by weight of the total weight of the composition:

PVC (PVAc) Resin	20-40%
Plasticiser	30-50%
Adhesion promoter	0.5 - 1.5%
Natural coated fillers	20-30%
Additives and Pigments	1-3%
Swelling Agent	1-3%
Phenolic resin (resorcin)	0.2-1.2%
Solvents	1-3%

Thickness of the coating varies for different vehicle.

For example Ford figo have:

Sl no.	Part name/area	Coating thickness (µm)
A	Front floor	665
B	Side extension member FR	127
C	Extension member rear floor	184
D	Front sill	321

Tata indica vista have (1.5 to 9) mm, Hyundai i10 underbody spray has (1 to 6) mm, while A-Star have (1.5 to 7) mm.

Types of undercoating:

• Now let us look at the various kinds of automotive underbody coating you can go for, for your vehicle.

Rubberized Underbody coating

Rubberized vehicle undercoating is easy to apply and offers sound-cushioning as well as protection from dust, moisture, and dings or dents.

In addition to your undercarriage, rubberized undercoating is also safe to use on wheel wells and quarter panels, and dries to a soft rubbery finish that prevents further rust, damage, or moisture seeps. The coating can be painted over and, if necessary for bodywork, can be easily removed with an undercoating removal spray.

Overall, rubberized coating is generally the best option for protecting your vehicle's undercarriage, as it provides the simplest and best protective measures against rust and moisture.

Wax Based Underbody Coating

A paraffin-based undercoating will be the cheapest and quickest option available with which to protect the undercarriage of your vehicle. However, keep in mind that it will wear off quicker than other types of undercoating and will need to be stripped and reapplied at least once every year.

Wax-based undercoatings never truly harden. During application, they drip or flow into seams and cracks to provide protective properties. They are usually available in a spray gun canister or in an aerosol can and offer at least a base protection in moderately humid climates.

Asphalt Based Automotive Undercoating

For standard vehicles, any of the aforementioned types of undercoating will provide sufficient protection. For large trucks and heavy machinery, asphalt-based undercoating provides a bit of extra durability against rocks, chips, and moisture.

Asphalt-based undercoating generally contains a little bit of rubberized material that sets up firmly and also helps soften noise. Generally sold in five gallon containers, this type of undercoating also needs more cure time than the other three, and is NOT paintable, making it best to use only for undercarriages.

Polyurethane Underbody coating

The other option for undercoating your vehicle is to use a polyurethane-based sealant. This type of vehicle undercoating is a little bit quicker and easier to apply.

Oftentimes, polyurethane undercoating will come in canisters ready to preload into an application gun. This type of sealant works by seeping into all cracks and seams, displacing salt and moisture and oozing around rusty areas to bond with and protect unoxidized metal. It also sands quickly in case you'll need to perform bodywork and can be painted over.

On the flipside, this type of car undercoating generally requires a little bit more surface prep work before applying sanding and applying an etching primer to bare metals before using are generally recommended.

Advantages of Underboady coating

• Undercoating gives an extra layer of protection against rust and corrosion, protecting your car.
• Undercoating will eventually wear out, but you can get years of protection from it. Even vehicles in warmer climates gain protection as debris is repelled and kept away from eating at the vehicle.
• It can be self-applied.
• It minimizes the sound from underneath the car.
• It insulates the interior of the car from the extreme temperature from beneath the vehicle.
• The coating does not chip away when hit by stones

Disadvantages of Underboady coating

• Undercoating will not help you if corrosion already exists and the corrosion needs to be removed first before it can be applied, which can be expensive for you.
• It must be reapplied every 3 to 5 years for the best results
• It adds weight to the vehicle.