How to Spray Finish and Buff a Guitar
A Comprehensive Step-by-Step Guide
Refinishing a guitar is a meticulous process that requires attention to detail and the right techniques. Whether you’re giving a new life to an old instrument or applying a finish to a custom build, following a structured approach is essential for achieving a professional-quality result. This guide provides an in-depth look at each step involved in spray finishing and buffing a guitar.
Materials and Tools Needed
Sandpaper: Grits 120, 150, 220, 320, 400, 600, 800, 1000, 1500, 2000
Tack Cloth: To remove dust and debris
Spray Gun or Aerosol Lacquer/Paint: Depending on your preference and available tools
Masking Tape: High-quality, low-tack tape to avoid damaging the surface
Buffing Compound: Polishing compounds such as medium, fine, and swirl remover
Polishing Cloth or Buffing Wheel: Preferably a foam or cotton wheel for fine finishes
Safety Equipment: Gloves, mask, and goggles to protect against fumes and particulates
Clean, Dust-Free Workspace: A well-ventilated area free of airborne dust and debris
Step 1: Prepare the Guitar
Preparation is critical to the final outcome of your guitar finish. Rushing through this step can lead to imperfections that are difficult to correct later on.
Remove All Hardware:
Start by completely disassembling the guitar. Remove the strings, pickups, knobs, and any other hardware. This prevents accidental overspray and ensures a clean, professional finish.
Store all parts safely in labeled containers to avoid losing any small components.
Inspect the Guitar Body:
Examine the guitar body for any dents, scratches, or imperfections. Small dents can often be raised with a damp cloth and a hot iron, while deeper gouges may require wood filler.
If the guitar has an existing finish, determine whether it needs to be completely removed or simply sanded smooth. If you're unsure, a complete refinish is often the safest choice for ensuring an even final coat.
Sanding the Surface:
Initial Sanding (Bare Wood or Stripped Finish): Start with 120-grit sandpaper to remove any remaining finish or rough spots. Move to 150-grit to refine the surface and eliminate any sanding marks from the coarser grit.
Shaping and Contouring: Use this opportunity to smooth out the guitar's edges and contours. Be cautious around binding and sharp edges; over-sanding can damage these areas.
Final Prep Sanding: Progress through 220, 320, and finally 400-grit sandpaper. Each subsequent grit should be used to remove the scratches left by the previous one. Sanding in the direction of the wood grain is crucial to avoid visible scratches under the finish.
Final Dusting: Use a tack cloth to carefully remove all dust and debris. Pay special attention to any small crevices or binding areas where dust can accumulate.
Step 2: Masking
Proper masking is essential to protect parts of the guitar that should not be finished.
Mask Off Delicate Areas:
Use high-quality masking tape to cover the fretboard, pickup cavities, and neck joint if you're finishing the body separately from the neck.
Ensure that the tape is firmly pressed down along the edges to prevent any finish from seeping under it.
Double-Check Masking:
Before proceeding, inspect your masking work to ensure no areas are left exposed that should be protected. Improper masking can result in tedious clean-up work later on.
Step 3: Apply the Finish
Applying the finish is where the guitar begins to take on its final appearance. The key is to apply thin, even coats, allowing each to dry properly before moving on to the next.
Choosing the Right Finish:
Lacquer: A traditional choice for guitar finishing, lacquer is valued for its ability to produce a high-gloss finish and its ease of repair. It dries quickly and is relatively easy to work with, making it ideal for those with some experience in spray finishing.
Polyurethane: More durable and resistant to wear, polyurethane is often chosen for its protective qualities. It’s less prone to chipping but can be more challenging to apply smoothly due to its thickness.
Other Finishes: Some builders may opt for oil finishes (such as Tru-Oil) or water-based finishes. These have different application techniques and properties, so be sure to research thoroughly if choosing an alternative finish.
First Coat - Sealer:
A sealer coat is vital to ensure that the subsequent layers of finish adhere properly. The sealer fills the wood’s pores, providing a smooth base for the finish.
If using a spray gun, adjust the settings for a fine mist. Hold the gun 6-8 inches away from the surface and apply the sealer in thin, even strokes. If using aerosol, apply with the same technique.
Allow the sealer coat to dry completely (usually about 1-2 hours, depending on humidity and temperature). The surface may feel slightly rough after drying, which is normal.
Sanding Between Coats:
Lightly sand the sealer coat with 400-grit sandpaper to smooth out any raised grain or roughness. Sand just enough to dull the sheen without cutting through the sealer to bare wood.
After sanding, clean the surface with a tack cloth to remove any dust.
Applying Build-Up Coats:
Apply 6-10 thin coats of lacquer or polyurethane, depending on the desired depth of the finish. Each coat should be light to avoid runs and sags.
Allow each coat to dry thoroughly. Lacquer typically dries in 30 minutes to an hour, but it’s best to wait 2-4 hours between coats for optimal results. Polyurethane may require more time between coats due to its thicker consistency.
Sand lightly with 600-grit sandpaper between each coat to ensure smooth application and remove any imperfections such as dust particles or orange peel texture.
Final Coats:
The final 2-3 coats should be applied with extra care. Switch to 800 or 1000-grit sandpaper for sanding between these coats to achieve a glassy smooth surface.
The last coat should be applied in an environment as free of dust as possible to avoid imperfections in the finish. Consider using a clean spray booth or a makeshift dust-free environment to control the conditions.
Step 4: Curing the Finish
After the final coat is applied, the finish needs time to harden and cure fully. This process is crucial for achieving a durable, long-lasting finish.
Allow Ample Curing Time:
Lacquer finishes typically require 7-14 days to cure fully, while polyurethane may need 2-4 weeks, depending on environmental conditions.
Store the guitar in a well-ventilated area with stable temperature and humidity levels. Avoid exposure to direct sunlight or extreme temperatures, as this can affect the curing process.
Test for Curing:
To check if the finish is fully cured, press your fingernail lightly into a hidden area of the guitar. If it leaves an indentation, the finish needs more time to cure. A fully cured finish will resist indentation and feel hard to the touch.
Step 5: Wet Sanding
Wet sanding is the process of leveling the finish to remove any imperfections and prepare it for buffing.
Soak Sandpaper:
Begin with 1000-grit wet/dry sandpaper. Soak it in water with a few drops of dish soap for lubrication. The soap helps reduce friction and prevents the paper from clogging with finish material.
Use a spray bottle to keep the surface wet while sanding.
Sand the Surface:
Sand the guitar body in circular motions, applying light pressure. The goal is to remove any orange peel texture, dust nibs, or small imperfections.
Frequently wipe the surface with a clean, damp cloth to check your progress. The finish should begin to take on a dull, uniform appearance as the high spots are leveled.
Move up through 1500-grit and then 2000-grit sandpaper, ensuring that each step removes the scratches left by the previous grit.
Final Wet Sanding:
The final wet sanding with 2000-grit should leave the finish incredibly smooth, with no visible scratches. At this stage, the surface will be dull, but it will have a uniform, consistent texture, ready for buffing.
Step 6: Buffing and Polishing
Buffing and polishing the finish brings out the shine and depth, creating a professional-looking, glossy surface.
Apply Buffing Compound:
Start with a medium-cut buffing compound to remove any remaining fine scratches from wet sanding. Apply a small amount to the surface or directly to the buffing pad.
If using a buffing wheel, choose a medium-firm foam pad. For hand buffing, use a soft, clean polishing cloth.
Buff the Surface:
Work in small sections, moving the buffer or cloth in circular motions. If using a machine buffer, keep the speed low (around 1000-1500 RPM) to avoid burning through the finish.
Apply light pressure and let the compound do the work. Buff until the surface starts to develop a glossy shine.
Wipe away any excess compound with a clean microfiber cloth.
Fine Polishing:
Switch to a fine polishing compound or swirl remover for the next stage. This step removes any micro-scratches left by the previous compound and enhances the gloss.
Buff the surface again, working slowly and carefully. This stage is crucial for achieving a mirror-like finish.
For the ultimate gloss, some luthiers use a glaze or ultra-fine polish as a final step.
Inspect and Touch-Up:
After buffing, inspect the guitar under good lighting to check for any missed spots or imperfections. If necessary, touch up these areas with additional polishing or a light buff.
Step 7: Reassemble the Guitar
With the finishing process complete, it’s time to reassemble the guitar and enjoy the fruits of your labor.
Remove Masking Tape:
Carefully peel away the masking tape, ensuring that no finish chips or peels away with it. Use a sharp blade to score the edge of the tape if necessary.
Reinstall Hardware:
Reinstall the pickups, bridge, knobs, and any other hardware you removed at the start. Take care not to scratch the new finish during reassembly.
Tighten screws and bolts evenly to avoid placing stress on the finish.
Final Setup:
Restring the guitar and perform a final setup, adjusting the action, intonation, and any other necessary settings. Your guitar should now look as good as it plays!
Conclusion
Spray finishing and buffing a guitar is a rewarding process that can transform the look and feel of your instrument. While it requires time, patience, and precision, the results are well worth the effort. By following these detailed steps, you can achieve a professional-quality finish that not only enhances the appearance of your guitar but also protects it for years to come.