Using Boiled Linseed Oil and 4F Pumice Powder

This guide explains how to make and use a professional-quality wood grain filler using boiled linseed oil and 4F grade pumice powder.
The 4F grade (very fine, approximately 75–100 microns) is strongly recommended for filling small pores without leaving a gritty residue.
It works exceptionally well on open-grained woods such as oak, ash, or walnut to create a mirror-smooth surface before applying varnish, shellac, or lacquer.

Materials Needed

  • Boiled Linseed Oil (BLO)
  • 4F Very Fine Grade Pumice Powder (any brand)
  • Clean cotton cloths or t-shirt rags
  • Rubber gloves and respirator (for dust safety)
  • Small bowl or dish for mixing
  • Soft brush or applicator pad
  • Optional: stain or pigment for tinting filler

Step-by-Step Instructions

  1. Prepare the Surface:
    Sand your wood to 180–220 grit. Remove all dust using a tack cloth or vacuum.

  2. Apply Boiled Linseed Oil:
    Wipe on a thin layer of boiled linseed oil using a clean cloth.
    The surface should look wet but not puddled.

  3. Add Pumice:
    While the oil remains wet, sprinkle a small amount of 4F pumice (about one teaspoon per square foot) onto the surface.

  4. Work the Mixture In:
    Rub the mixture into the wood pores using a circular motion with a soft cloth.
    As the pumice mixes with the oil and wood dust, it forms a slurry that fills the pores evenly.

  5. Optional — Tint the Mixture:
    For colored grain filling, mix an oil-based stain or artist’s oil pigment directly into the linseed oil before adding the pumice.
    This creates a tinted filler that can darken the pore contrast or match the overall tone of your project.
    Stir thoroughly before applying to ensure even color distribution.

  6. Wipe Off Excess:
    Once the pores are filled, wipe across the grain to remove surface residue.
    Avoid leaving any layer of filler to dry on the surface.

  7. Dry and Cure:
    Let the surface dry for 48–72 hours. The filled surface should feel smooth and firm to the touch before proceeding.

  8. Inspect and Repeat:
    Check the surface under low-angle (raking) light. Reapply the filler to any remaining open pores.

  9. Final Sanding and Finish:
    After full curing, lightly sand with 320 grit, then apply your chosen finish such as shellac, varnish, or lacquer.

Important Note on Stained Surfaces

Avoid applying this filler mixture on already-stained wood.
The rubbing action required to fill the pores can lift or smear the color, creating uneven tone.
If you intend to both stain and fill the wood, perform the filling step first, allow it to cure completely, and then apply stain over the filled surface.

Tips and Notes

  • 4F pumice (~75–100 µm) is ideal for fine pore filling; coarser grades may leave visible scratches.
  • Use minimal oil — excess oil slows drying and may cause tackiness.
  • Always dispose of oil-soaked rags safely (store in water or an airtight metal container).
  • Work in a ventilated area.
  • Inspect under raking light to confirm all pores are completely filled before applying finish coats.

Where to Buy 4F Pumice Powder

Supplier Typical Size Approx. Price (USD) Website
Amazon 1 lb – 5 lb $10 – $25 amazon.com/s?k=4F+pumice+powder
His Glassworks 1 lb – 20 kg $2 – $40 hisglassworks.com
Wm. S. McCaw Co. 1 lb $14.50 mccawcompany.com
Lapidary Mart 50 lb $73.00 lapidarymart.com
Etsy (WellerMart) 4 oz $6.00 etsy.com/listing/1241687706

Always verify that the product is labeled as 4F (very fine) grade.
Avoid generic pumice intended for cleaning or horticultural use — these are too coarse for wood finishing.

Final Advice

Before applying to your main project, always test the filler process on a scrap piece of the same wood species.
Properly filled and sanded surfaces will produce a flawless, mirror-smooth foundation for your final finish.