Using an orbital sander is an effective way to remove varnish from flat surfaces. Here's how to do it properly:
Preparation is Key
Before you begin, ensure you have the following:
- Orbital Sander: A random orbit sander is recommended for its ability to prevent swirl marks.
- Sandpaper: Start with coarser grits like 150 to remove the bulk of the varnish, then move to finer grits like 220 for a smooth finish. Have multiple grits available.
- Dust Mask/Respirator: Essential for protecting your lungs from dust particles.
- Safety Glasses: To protect your eyes from flying debris.
- Tack Cloth or Damp Rag: For removing dust between sanding sessions.
- Work Area Protection: Cover surrounding surfaces with drop cloths to prevent dust contamination.
Sanding Process: Step-by-Step
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Secure the Workpiece: Ensure the object you are sanding is stable and won't move during sanding. Use clamps if necessary.
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Choose the Right Grit: Begin with 150-grit sandpaper to remove the existing varnish layer. This will aggressively remove the varnish without gouging the wood too deeply.
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Attach Sandpaper: Securely attach the sandpaper to the orbital sander according to the manufacturer's instructions.
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Sanding Technique:
- Apply Light Pressure: Let the sander do the work; avoid pressing down too hard. Heavy pressure can damage the wood and shorten the life of the sandpaper.
- Move in Overlapping Passes: Sand in a consistent, overlapping pattern to ensure even removal of the varnish. Avoid staying in one spot for too long, as this can create depressions.
- Keep the Sander Flat: Maintain a flat and consistent angle to prevent uneven sanding.
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Check Your Progress: After a few passes, stop and inspect the surface. Ensure you are removing the varnish evenly.
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Switch to Finer Grits: Once the majority of the varnish is removed with the 150-grit paper, switch to 220-grit sandpaper to smooth the surface and remove any scratches left by the coarser grit.
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Dust Removal: After each sanding session (especially before switching grits), remove dust particles with a tack cloth or a lightly dampened rag. This helps to see the progress and prevents scratching from trapped dust.
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Irregular surfaces: For irregular surfaces or corners where the orbital sander cannot reach, use handheld sandpaper or a sanding block with the same grits you used with the sander.
Important Considerations:
- Dust Collection: If your orbital sander has a dust collection system, use it to minimize dust in the air.
- Varnish Type: Different varnishes may require different approaches. Older, brittle varnishes may require more aggressive sanding initially.
- Wood Type: Be careful when sanding softwoods, as they are more prone to damage from aggressive sanding.
Final Steps
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Final Dusting: After sanding with the 220-grit sandpaper, thoroughly remove all dust with a tack cloth.
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Inspection: Carefully inspect the surface for any remaining varnish or imperfections. Resand if necessary.
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Preparation for Finishing: The surface is now ready for staining, painting, or applying a new finish.
