What Sandpaper Grit Do I Use?
Not sure what sandpaper grit to use? This guide explains the best grit ranges for fiberglass repair, gelcoat, primer, marine paint, fairing compound, wet sanding, polishing, and general surface preparation.
At Fiberglass Florida, we help boatyards, fiberglass repair shops, marine painters, surfboard builders, composite fabricators, and DIY boat owners choose the correct abrasive for the job. The right sandpaper grit can save time, improve adhesion, reduce deep scratches, and help create a cleaner final finish.
Quick Answer: What Sandpaper Grit Should I Use?
Use 24–36 grit for aggressive grinding, removing damaged fiberglass, heavy coating removal, and fast material removal.
Use 40 grit for heavy fairing, shaping repairs, removing gelcoat, and rough fiberglass prep.
Use 80 grit as a strong all-around grit for fiberglass repair, fairing work, sanding old coatings, and general prep.
Use 120–220 grit for middle-stage sanding, smoothing filler, refining repairs, and preparing for primer.
Use 320–400 grit for primer sanding, marine paint prep, Awlgrip prep, and finer surface refinement.
Use 600–1200 grit for gelcoat repair, wet sanding, orange peel removal, and polishing prep.
Use 1500–2000+ grit for dark gelcoat, high-gloss polishing, and final finish refinement.
Sandpaper Grit Chart
The lower the grit number, the more aggressive the sandpaper. The higher the grit number, the finer the scratch pattern. Use coarse grits for removal and shaping, medium grits for prep, and fine grits for wet sanding or polishing.
| Grit Range | Best Use | Common Marine, Fiberglass & Composite Applications |
|---|---|---|
| 24–36 Grit | Aggressive grinding | Heavy fiberglass grinding, damaged laminate removal, thick coating removal, beveling repairs, fast material removal |
| 40 Grit | Heavy shaping and fairing | Fairing compound shaping, removing gelcoat, rough sanding, flattening high spots, aggressive repair prep |
| 80 Grit | All-around fiberglass prep | Fiberglass repair prep, smoothing grinder marks, sanding old coatings, preparing bonding surfaces, general shop sanding |
| 120–150 Grit | Middle-stage sanding | Smoothing filler, refining fairing compound, leveling repaired areas, preparing surfaces before primer |
| 180–220 Grit | Primer prep and surface refinement | Final sanding before primer, smoothing repairs, sanding between build coats, refining fairing work |
| 320–400 Grit | Paint and topcoat prep | Sanding primer before marine paint, Awlgrip prep, Awlcraft prep, gelcoat prep, final coating prep |
| 600 Grit | Fine leveling | Gelcoat repair leveling, orange peel reduction, fine wet sanding, first step before higher polishing grits |
| 800–1200 Grit | Wet sanding and polishing prep | Gelcoat touch-ups, scratch refinement, polishing prep, light-color gelcoat finishing, removing sanding marks before compound |
| 1500–2000+ Grit | Final finish sanding | Dark gelcoat finishing, high-gloss polishing, final scratch refinement, premium finish work before compound and polish |
What Grit Sandpaper Should I Use for Fiberglass?
For fiberglass repair, start coarse enough to create a strong mechanical surface. Most fiberglass repairs use 40–80 grit, depending on how much material needs to be removed.
Fiberglass Repair Grit Guide
- 24–36 grit: Heavy grinding, damaged laminate removal, and beveling large fiberglass repairs
- 40 grit: Heavy shaping, gelcoat removal, and rough repair prep
- 80 grit: General fiberglass repair prep, sanding old coatings, and smoothing coarse grinder marks
- 120–150 grit: Smoothing cured laminate, filler, and repaired edges
- 180–220 grit: Final prep before primer or additional fairing
Important: For bonding fiberglass, resin, filler, or fairing compound, avoid sanding too fine. Resin and repair materials need mechanical tooth to bond properly.
What Grit Sandpaper Should I Use for Transom, Stringer, or Floor Repair?
For larger fiberglass repairs such as transoms, stringers, floors, bulkheads, and structural patches, coarse grits are usually required. These repairs often involve removing damaged fiberglass, grinding back existing laminate, cleaning bonding areas, and shaping new material.
- 24–36 grit: Fast removal of damaged laminate or heavy buildup
- 40 grit: Beveling repair areas and shaping rough fiberglass
- 80 grit: General bonding prep before new fiberglass, resin, or filler
- 120 grit: Smoothing repaired areas before fairing or primer
For structural repair work, the surface should be clean, dry, dull, and properly sanded before resin or fiberglass is applied.
What Grit Sandpaper Should I Use Before Gelcoat?
The correct grit for gelcoat depends on whether you are applying new gelcoat or sanding cured gelcoat before polishing.
Before Applying Gelcoat
- 80 grit: Heavy prep or repair areas where gelcoat or laminate needs strong mechanical tooth
- 120–180 grit: General sanding before gelcoat application
- 220 grit: Fine prep on smoother surfaces, depending on the repair and coating system
After Applying Gelcoat
- 400–600 grit: Level orange peel, dust nibs, brush marks, or rough cured gelcoat texture
- 800–1000 grit: Refine scratches before compound
- 1200 grit: Common finishing point for many light-colored gelcoat repairs before compound and polish
- 1500–2000+ grit: Extra refinement for dark gelcoat colors or high-gloss finishes
What Grit Sandpaper Should I Use Before Primer?
For marine primer, most surfaces are sanded between 120 and 220 grit before primer, depending on the coating system, substrate, and primer type.
- 80–120 grit: Heavy prep, old coatings, repairs, or rough fiberglass surfaces
- 150–180 grit: General primer prep
- 220 grit: Fine primer prep on smoother surfaces
- 320 grit: Sanding certain primers before topcoat, depending on the system
Always check the primer manufacturer’s technical data sheet. Different primers may require different sanding profiles for proper adhesion and finish quality.
What Grit Sandpaper Should I Use Before Awlgrip, Awlcraft, or Marine Paint?
For Awlgrip, Awlcraft 2000, Awlcraft 3000, and other marine topcoats, the correct grit depends on the primer, application method, and coating system. Many marine topcoat systems use primer finished in the 320–400 grit range before paint, but always follow the current application guide for the exact system being used.
For more detailed Awlgrip surface preparation, reducer, primer, and topcoat information, visit our Awlgrip Application Guide.
You can also shop related Awlgrip products here:
- Awlgrip Topcoat
- Awlcraft 2000 & Awlcraft 3000
- Awlgrip 545 Epoxy Primer White Base D8001
- Awlgrip High Build Epoxy Primer
What Grit Sandpaper Should I Use for Fairing Compound?
Fairing compound is usually shaped with coarse to medium grits, then refined before primer. Starting too fine can make the job slower and clog the abrasive faster.
- 40 grit: Heavy fairing, flattening high spots, and rough shaping
- 80 grit: General fairing compound shaping and leveling
- 120–150 grit: Smoothing and refining the repair area
- 180–220 grit: Final sanding before primer
For large flat areas, use a longboard or rigid sanding block to keep the surface fair. A power sander can remove material quickly, but a long board helps reveal waves, highs, and lows.
What Grit Sandpaper Should I Use for Polishing Gelcoat?
If gelcoat is dull, oxidized, scratched, or has orange peel, wet sanding may be needed before compound and polish. The goal is to remove defects while leaving the finest scratch pattern possible before polishing.
- 400 grit: Heavy leveling for rough gelcoat or significant orange peel
- 600 grit: Moderate correction and leveling
- 800 grit: Scratch refinement and wet sanding progression
- 1000 grit: Fine sanding before compound
- 1200 grit: Common finishing grit for many light-colored gelcoat repairs
- 1500–2000+ grit: Better refinement for dark gelcoat, newer boats, or higher-gloss finishes
Do not start too aggressive unless needed. For light oxidation, compound and polish may be enough without sanding.
What Sanding Tool Should I Use?
The best sanding tool depends on the size of the job, the shape of the surface, and how much material you need to remove.
| Tool | Best Use | Common Grits |
|---|---|---|
| DA Sander / Dual-Action Sander | General sanding, fiberglass prep, smoothing repairs, primer prep | 80, 120, 180, 220, 320 |
| 4-1/2 Inch Grinder | Heavy fiberglass grinding, removing old material, beveling repairs | 24, 36, 40, 80 |
| Variable-Speed Rotary Tool / Buffer with Backing Pad | Large-area sanding, heavy fairing, controlled material removal | 40, 80, 120 |
| Longboard / Long Sanding Block | Fairing long panels, flattening surfaces, finding highs and lows | 40, 80, 120, 180, 220 |
| Flexible Sanding Block | Curved hulls, rounded edges, gelcoat repairs, hand sanding | 80 through 1200+ |
| Small Detail Block / Stir Stick / PVC Pipe | Small holes, tight areas, gelcoat dings, curves, detail sanding | 80, 120, 220, 400, 600, 1200 |
| Die Grinder / 90-Degree Grinder | Corners, holes, tight spots, detailed fiberglass shaping | 36, 40, 80 |
Velcro Sandpaper vs. Sticky-Back Sandpaper
For many fiberglass and gelcoat jobs, hook-and-loop sandpaper is a practical choice because it can be removed, repositioned, and reused more easily than sticky-back paper. Hook-and-loop discs also work well when switching between grits or using the same abrasive on different blocks or sanding pads.
Sticky-back paper can still be useful, but moisture from wet sanding can make adhesive-backed paper harder to manage. For wet sanding gelcoat repairs, wet/dry sheets wrapped around a block are often the easiest option.
Dry Sanding vs. Wet Sanding
When Should I Dry Sand?
Dry sanding is usually used for fiberglass repair, fairing compound, primer prep, paint prep, and general surface preparation. Dry sanding works especially well with vacuum-assisted sanders and dust extraction systems.
When Should I Wet Sand?
Wet sanding is commonly used for gelcoat finishing, clear coat correction, polishing prep, and very fine scratch removal. Wet sanding helps reduce clogging and produces a finer finish before compound or polish.
Recommended Sanding Steps by Project
| Project | Starting Grit | Finish Grit |
|---|---|---|
| Fiberglass repair prep | 40–80 | 80–120 before bonding |
| Transom, stringer, or floor repair | 24–40 | 80 before new laminate or filler |
| Fairing compound shaping | 40–80 | 180–220 before primer |
| Primer prep | 120–180 | 220–320 depending on system |
| Topcoat prep | 220–320 | 320–400 depending on paint |
| Gelcoat repair finishing | 400–600 | 1200 for many light colors, 1500–2000+ for dark colors |
| Polishing prep | 800–1000 | 1500–2000+ |
Common Sandpaper Mistakes
- Starting too fine: Fine grits will not remove material fast enough and can waste time.
- Starting too coarse: Aggressive grits can leave deep scratches that require extra steps to remove.
- Skipping too many grits: Jumping from 40 grit straight to 400 grit can leave scratches behind.
- Sanding bonding areas too smooth: Fiberglass, resin, filler, and fairing compound need a proper mechanical profile.
- Using the wrong tool: A grinder removes material quickly, but a longboard is better for keeping panels straight and fair.
- Not cleaning between grits: Dust and loose particles can create scratches during the next sanding step.
- Ignoring PPE: Fiberglass dust, gelcoat dust, and paint dust should be controlled with proper protection and ventilation.
Safety Tips for Sanding Fiberglass, Gelcoat, and Paint
Sanding fiberglass, gelcoat, primer, paint, and filler creates dust. Always use proper eye protection, gloves, and respiratory protection. For larger sanding jobs, dust extraction and a properly fitted respirator are strongly recommended.
When using grinders or aggressive sanding tools, keep guards in place whenever possible, use the correct backing pad, and avoid forcing the tool. Let the abrasive do the work.
Sandpaper and Abrasives for Florida Boatyards, Marine Repair Shops, and Fiberglass Work
Fiberglass Florida supplies sandpaper, sanding discs, abrasive sheets, rolls, polishing products, and surface preparation materials for marine repair shops, boatyards, fiberglass fabricators, composite shops, yacht refinishers, surfboard builders, and DIY boat owners across Florida.
With locations in Rockledge and Stuart, we support customers throughout the Space Coast, Treasure Coast, Orlando area, Port Canaveral, Merritt Island, Melbourne, Cocoa, Vero Beach, Fort Pierce, Palm City, and surrounding Florida marine markets.
Whether you are sanding fiberglass repairs, preparing gelcoat, leveling primer, refinishing a hull, restoring oxidized gelcoat, or prepping a surface for Awlgrip, Awlcraft, Interlux, or another marine coating system, our team can help you choose the correct sandpaper grit and abrasive type for the job.
Shop Sandpaper and Abrasives at Fiberglass Florida
Fiberglass Florida stocks professional sandpaper, sanding discs, abrasive sheets, abrasive rolls, wet/dry sandpaper, polishing products, backing pads, and surface preparation supplies for marine, fiberglass, composite, automotive, and industrial finishing work.
We carry abrasive options from trusted brands including Mirka, Indasa, and 3M. Our abrasive selection supports dry sanding, wet sanding, dust-free sanding, primer prep, gelcoat repair, marine paint prep, composite finishing, and final polishing.
Shop related abrasive categories and brands:
- Mirka Abrasives
- Indasa Sandpaper
- 3M Sandpaper
- Sanding Discs
- Wet/Dry Sandpaper
- Polishing Compounds and Pads
Need help choosing the right grit? Call 321-639-3046 or visit Fiberglass Florida in Rockledge or Stuart.
Frequently Asked Questions About Sandpaper Grit
What is the best all-around sandpaper grit for fiberglass?
80 grit is one of the best all-around grits for fiberglass repair and general prep. It is aggressive enough to prep surfaces, remove material, and clean up rough sanding marks without being as extreme as 24, 36, or 40 grit.
What grit sandpaper should I use for fiberglass repair?
For fiberglass repair, 40–80 grit is commonly used to open the surface and create a strong mechanical bond. Heavy grinding or damaged laminate removal may require 24–36 grit.
What grit should I use before applying fiberglass resin?
Before applying fiberglass resin, use a coarse surface profile, commonly 40–80 grit. Avoid sanding too smooth before bonding because resin needs mechanical tooth to grip the surface.
What grit should I use before gelcoat?
Before applying gelcoat, 80–180 grit is commonly used depending on the repair area and surface condition. For finer prep, 220 grit may be used when appropriate.
What grit should I use to wet sand gelcoat before polishing?
Gelcoat is often wet sanded with 800–1200 grit before compound and polish. For heavier orange peel or defects, you may need to start around 400–600 grit and work finer. Dark gelcoat may benefit from 1500–2000+ grit before polishing.
What grit should I use before primer?
For primer prep, 120–220 grit is common before primer. After primer, many systems are sanded with 220–400 grit before topcoat, depending on the primer and paint system.
What grit should I use before painting a boat?
Many marine paint systems use primer finished in the 320–400 grit range before topcoat. Always confirm with the paint manufacturer’s application guide for the exact coating system.
What grit should I use for fairing compound?
Fairing compound is usually shaped with 40–80 grit, smoothed with 120–150 grit, and finished with 180–220 grit before primer.
Should I use a DA sander or a grinder?
Use a grinder for heavy fiberglass removal, aggressive shaping, and fast material removal. Use a DA sander for general sanding, surface prep, smoothing scratches, and more controlled finish work.
Should I use a longboard for fairing?
Yes. A longboard or long sanding block helps keep large panels straight and fair. Power sanders remove material quickly, but longboards are better for finding highs, lows, waves, and uneven areas.
Can I skip sandpaper grits?
You can step through grits, but avoid large jumps. Skipping from a coarse grit directly to a very fine grit may leave deep scratches that show through primer, paint, gelcoat, or polish.
Should I wet sand or dry sand?
Dry sanding is usually used for fiberglass repair, fairing, primer prep, and paint prep. Wet sanding is usually used for gelcoat finishing, polishing prep, clear coat correction, and very fine scratch removal.
What grit removes scratches before polishing?
For gelcoat or painted surfaces, use the least aggressive grit needed. Common polishing prep grits include 1000, 1200, 1500, and 2000 grit, followed by compound and polish.
Validate your login