Choosing the right grit size is one of the most important decisions in sand blasting. The grit size directly affects cleaning speed, surface roughness, coating adhesion, and abrasive consumption. Using the wrong grit can lead to under-blasting, excessive roughness, coating failures, and higher costs.
At Aerowheel Surface Finishing, we guide industries in selecting the ideal abrasive grit size based on their material type, contamination level, and finishing requirement. This article explains how grit size works and how to choose the correct one for your application.
1. What Is Grit Size in Sand Blasting?
Grit size refers to the particle size of the abrasive material used in blasting.
It determines:
- How deeply the abrasive cuts into the metal
- The anchor profile or texture created on the surface
- Blasting speed and efficiency
Smaller grit size = fine finish and low roughness
Larger grit size = aggressive cutting and high roughness
Selecting the correct size ensures proper surface preparation before painting, coating, or plating.
2. Choosing Grit Size Based on Application
Different applications need different surface profiles. Here is a simple guide:
a. Heavy Rust, Mill Scale, Thick Paint
Use large grit for aggressive cleaning.
Recommended size:
- G18 – G24
- Removes deep rust and scale
- Creates strong anchor profile for coatings
Ideal for:
- Structural steel fabrication
- Ship hulls
- Bridges
- Heavy industrial equipment
b. General Cleaning and Surface Preparation
Use medium grit for balanced cleaning and finish.
Recommended size:
- G25 – G40
- Good for standard SA 2.5 surface
- Uniform finish
Ideal for:
- Painting and powder coating
- Fabrication parts
- Machine components
c. Precision Finishing, Polishing, Deburring
Use small grit for fine finishing.
Recommended size:
- G50 – G80
- Leaves low roughness
- Improves coating appearance
Ideal for:
- Stainless steel
- Aluminum parts
- Auto components
- Export furniture and metal décor
3. Choosing Grit Size Based on Coating Type
Different coatings need different surface textures to bond properly.
a. Thick Coatings
(Epoxy, polyurethane, fireproof coatings)
Need deep anchor profile for grip.
Recommended grit:
- G18 – G30
b. Standard Industrial Paint
(Primer + topcoat systems)
Needs medium anchor profile.
Recommended grit:
- G25 – G40
c. Powder Coating
(Powder bonding)
Needs fine, uniform texture.
Recommended grit:
- G40 – G60
d. Galvanizing
(Zinc coating immersion)
Needs clean, rough surface without deep cutting.
Recommended grit:
- G30 – G40
Correct grit ensures better coating adhesion and long service life.
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4. Choosing Grit Size Based on Material
Abrasive impact varies by material hardness.
a. Hard Materials
(Mild steel, cast iron)
Handle large grit easily.
Recommended:
- G18 – G40
b. Soft Materials
(Aluminum, brass, copper)
Large grit may embed into the surface.
Recommended:
- G50 – G80
or glass beads
c. Stainless Steel
Needs clean surface without contamination.
Recommended:
- G40 – G80
or aluminum oxide
Selecting the right size preserves material integrity.
5. Impact of Grit Size on Surface Roughness (Ra & Rz)
Grit size defines roughness which coating manufacturers specify as Ra or Rz.
- Larger grit = higher Ra values
- Smaller grit = lower Ra values
Example:
| Grit Size | Surface Roughness |
|---|---|
| G18 | High (coarse finish) |
| G24 | Medium-high |
| G40 | Medium |
| G60 | Fine finish |
Matching roughness with coating specs avoids adhesion failures.
6. How to Select Grit Based on Blasting Method
Wheel Blasting Machines
Work best with steel grit/shot sizes:
- G18–G40
- Fast cleaning
- High recycling rate
Air Blasting Machines
Support more abrasive types:
- Steel grit
- Aluminum oxide
- Garnet
- Glass beads
- Size varies G25–G80, based on application
Choosing the right grit improves recycling efficiency, reducing abrasive cost.
7. Practical Tips for Selecting the Right Grit
- Always follow coating supplier recommendations
- For unknown jobs, start with medium grit (G25–G40)
- Avoid mixing grit sizes (reduces consistency)
- Monitor surface profile regularly
- Change grit size if cycle time increases
- Use hard grit for rust removal and fine grit for finishing
Most industries standardize on G25 and G30 for general structural work.
8. Test & Adjust for Best Results
Real-life testing gives the best result.
Do a small trial on sample pieces:
- Check cleaning speed
- Measure surface roughness
- Apply a small coat
- Test adhesion
If roughness is too high → reduce grit size
If contamination remains → increase grit size
Blasting parameters like pressure, angle, and distance also affect final results.
Conclusion
Choosing the correct grit size is simple when you match it with your application, coating type, and material. The right grit size ensures:
- Faster cleaning
- Consistent surface profile
- Better coating adhesion
- Long-lasting corrosion protection
- Lower abrasive consumption
At Aerowheel Surface Finishing, we help industries select abrasive sizes that deliver optimal surface quality and productivity for sand blasting operations.
