Underbody Coating

Underbody coatings

What an Underbody coating or sealant is?

Underbody coatings or sealants are generally a tougher paint which is designed to give protection to areas of the car which aren’t exposed much, such as the bottom of the car, front frames and inside the wheel arches. These coating have nothing to do with the aesthetics or the looks but are present to take up beatings from debris and stones as the car hovers past them. This coating is generally flexible and can absorb impacts and makes up for an ambient cabin.

Why Underbody coatings?

• Minimizes Sound: It minimizes the sound from underneath the car resulting a noiseless, smooth driving experience.
  
  Heat Insulation: It insulates the interior of the car from extreme temperatures from beneath the vehicle providing a comfortable cabin experience.
  
  Anti-corrosion: These coating makes the BIW less exposed to the environment thus prevent corrosion due to moisture.

Where it’s done?

Underbody coatings are a standard in automobiles for decade now. But the precision, coating materials, coat area and thickness of coat differs from automaker to automaker and from automobiles to automobiles. To keep costs under check some automakers shy away from making proper coats. In developing countries, comfortable cabin in a luxury and so is such coatings.

Generally, for the coating thickness isn’t uniform all over the underbody. For instance, Ford Figo gets a 650 – 700 micrometre coats in its front frame and gets a coat thickness of 300 micrometre in its front sill.

Parts generally that are coated:

1. Front chassis members
2. Front sill
3. Main floor
4. Rear floor and petrol tank
5. Rear wheel arches
6. Front wheel arches and wings
7. Behind the lights
8. Behind front valence

How and when it’s done

Post BIW is build a automobile manufacturing facility:

These steps take place post the BIW of the car is made.

Figure:  Underbody coating process at an OEM

So, our interest area here is the Underbody coat and its done post primer and before final paint job.

Though undercoats are done during manufacturing, they tend to thin out with time and needs to be redone to give a extend life to the automobile. Thus, many car body workshops and dealerships offer recoating of underbody.

Steps involved in re-coating:

On a fairly new car, covering the underbody with sealing compound will discourage corrosion. It can be sprayed on under pressure or brushed on. But if there is already considerable rust, applying a sealant will accelerate corrosion rather than protect the underbody against it, because the corrosion will spread unseen and unchecked beneath the covering layer. A sealant will be effective only if the underside of the car is completely clean.

 Masking involves covering parts of systems attached to or passing beneath the underbody, such as the exhaust system, hydraulic pipes, and the moving parts of the braking and suspension systems.

Thickness of Undercoating:

Earlier in this report it was mentioned that thickness of the undercoat isn’t consistent throughout, yes its that way but why? There are some parts that are more critical to car integrity and strong, take for instance the front frame. So such parts are given more thickness compared to the rest.

 The order of thickness of coats is as follows:

Types of underbody coats:

Bitumen coat:

These the oldest and cheapest available options and are rarely seen in current generation cars, as they tend to have a lesser lifespan than the other coat types. Though they provide good protection to the BIW, they tend to become brittle with time and breaks to create pores for moisture to seep in.

Resin coat:

Resin based coats are mostly polyurethanes can have better sound dampening and moisture resistant due to its physical nature and thus are the most widely used in the current times.

 Conclusion

Underbody coatings are an essential for durability and noise isolation a purpose. Neglecting them may require replacing main components ruptured by corrosion due to environmental conditions. Thus checking the underbody especially before and after monsoon can save tons of money in the long run.