Why Tar Sticks to Your Car (And Why Shampoo Won’t Remove It)
Detailing Chemistry Explained
Breaking down the science behind modern car care.
If you’ve ever washed your car and noticed small black spots still stuck to the paintwork, you’ve likely encountered road tar contamination — and wondered why tar sticks to your car in the first place.
These stubborn spots often appear on lower panels, behind wheels and along the rear of the vehicle.
Even after using snow foam, shampoo, or traffic film remover, they can remain firmly attached to the surface.
In this article we’ll explain:
• what tar contamination actually is
• why normal detergents won’t remove it
• how tar removers dissolve it safely
• where tar removal fits in the wash process
What Is Road Tar?
Road tar contamination is made up of bitumen particles thrown from the road surface.
These particles typically originate from:
• asphalt road surfaces
• road repairs
• warm weather softening road bitumen
• tyre spray from surrounding traffic
When these particles hit the vehicle, they adhere to the clear coat surface, forming small black dots that can be difficult to remove.
Road tar typically collects on lower panels and behind the wheels.
Why Shampoo Won’t Remove Tar
Most car shampoos and pre-wash products are designed to remove:
• dirt
• dust
• traffic film
• oily road residues
These contaminants can be lifted by detergents and surfactants.
However tar contamination is made from bitumen, a heavy hydrocarbon material derived from crude oil.
Because of this, it behaves more like adhesive residue than normal dirt.
Detergents alone cannot dissolve it effectively.
How Tar Removers Work
Tar removers work using hydrocarbon solvents that can dissolve bitumen safely.
These solvents penetrate the tar deposits and begin to soften them.
As the tar dissolves, the contamination can be wiped or rinsed away without excessive scrubbing.
This is why tar removers often appear to make the tar spots “bleed” or soften before removal.
Tar removers dissolve bitumen contaminants allowing for safer removal without aggressive contact.
Where Tar Removal Fits in the Wash Process
Tar removal usually takes place after washing the vehicle, once loose contamination has been removed.
Typical sequence:
↓
Contact wash
↓
Tar remover
↓
Iron fallout remover
↓
Final rinse
Removing tar before iron fallout helps expose any metallic contamination hidden beneath bitumen deposits.
--------------------
Summary
Tar contamination is made from bitumen particles thrown from road surfaces.
Because tar is a heavy hydrocarbon material, it cannot be removed effectively with normal detergents.
Dedicated tar removers use solvents to dissolve bitumen safely, allowing the contamination to be removed without damaging the paint.
Understanding how different contamination types respond to different chemistry is a key part of professional vehicle care.
Frequently Asked Questions
What is tar contamination on a car?
Tar contamination is made up of sticky, oil-based residues from road surfaces, including bitumen, asphalt, and adhesives. These particles bond strongly to paintwork and are not removed by normal washing.
Why doesn’t shampoo or snow foam remove tar?
Tar is hydrophobic, meaning it does not dissolve in water. Standard shampoos and snow foams are designed to remove general dirt, not heavy oil-based contamination.
Do I always need a tar remover?
If tar spots are visible or the paint feels rough after washing, a dedicated tar remover is the safest and most effective solution.
Can tar damage my paint?
Tar itself won’t immediately damage paint, but leaving it in place can lead to staining, increased contamination build-up, and more difficult cleaning over time.
When should tar removal be done?
Tar removal should be carried out after the pre-wash and contact wash stages but before applying protection.
Recommended Products
Tar contamination requires solvent-based cleaning supported by effective pre-wash stages. For best results, consider using products from our Paintwork Decontamination range:
Part of the Detailing Chemistry Explained Series
Author
Written by Kevin
Kev works in product development at MossChem developing professional car care formulations. Through the Detailing Chemistry Explained series he breaks down the science behind how detailing products actually work.