The grade of clay bar you should use on your car depends on the condition of your vehicle's paint and the level of contamination. Clay bars come in different grades, typically categorized as fine, medium, and heavy. Here’s a breakdown of when to use each grade:

Fine Grade Clay Bar

Use If:

• Your car is relatively new or well-maintained.
• The paint has light contamination such as dust, light tar spots, and minor environmental fallout.
• You are performing regular maintenance and want to maintain a smooth, clean surface without removing too much clear coat.

Advantages:

• Gentle on the paint and less likely to cause marring.
• Suitable for frequent use.

Medium Grade Clay Bar

Use If:

• Your car has moderate contamination such as tree sap, industrial fallout, light overspray, and more noticeable environmental contaminants.
• The paint feels rough to the touch in certain areas but is generally in good condition.

Advantages:

• Effective at removing a broader range of contaminants without being too aggressive.
• Balances effectiveness and safety for most vehicles.

Heavy Grade Clay Bar

Use If:

• Your car has heavy contamination, such as paint overspray, stubborn tar spots, or industrial fallout that a medium or fine grade clay bar cannot remove.
• The paint surface feels significantly rough and has not been decontaminated in a long time.

Advantages:

• Highly effective at removing the toughest contaminants.
• Can restore very contaminated surfaces to a smooth state.

Drawbacks:

• More likely to cause marring or scratching, requiring follow-up polishing.
• Should be used with caution, especially on delicate or older paint.

Recommendations

1. Start with a Fine or Medium Grade: If you are unsure of the level of contamination or if it’s your first time using a clay bar, starting with a fine or medium grade is usually a safer choice.
2. Test in a Small Area: Always test the clay bar in a small, inconspicuous area first to see how it affects the paint and to gauge its effectiveness at removing contaminants.
3. Use Lubrication: Always use a proper clay lubricant to minimize the risk of marring or scratching the paint.
4. Follow Up with Polishing: If you use a medium or heavy grade clay bar and notice any marring, follow up with a polishing step to restore the paint’s smoothness and gloss.

Choosing the right grade of clay bar and using it correctly will help you achieve a clean, smooth paint surface without causing damage.