Repairing defects before finish

Overview

Finish shows every dent, gouge, glue smear and open knot more than bare wood does, and stain reveals them most of all. Popular Woodworking's cabinet-grade finishing guide lists the preparation as sanding, steaming out dents, filling gouges and dealing with glue seepage. This entry covers the repairs the sources describe, and says where a repair will show under stain, because wood filler and epoxy do not take stain the way wood does.

When to use

After machining and a first sanding, and before the final grit and any stain. Flexner's purpose of sanding includes removing dents and gouges introduced in handling (Sanding schedule). For veneer sand-through see Finishing veneers; for glue see Glue squeeze-out and common finish failures; for deeper structural repair, see a furniture repair reference, which this guide does not cover.

Materials and tools

Water and a hot iron or soldering iron for dents; solvent-based or water-based wood putty; "Color Putty" for nail holes; clear epoxy and tape for loose knots; a putty knife; sandpaper and a block.

Steps

1. Dents (fibres crushed, not cut). Drip water into the depression and touch it with a hot object, such as a soldering iron, to turn the water to steam (Cabinet-Grade Finishing). A related approach from the linseed-paint article: drop water in the dent, let the wood absorb it, then press a hot iron over a damp cloth so steam is forced into the fibres, which will often pop the dent back up.
2. Gouges. These cannot be steamed because wood is missing: fill with solvent-based or water-based wood putty (Cabinet-Grade Finishing). Michael Dresdner (American Woodworker) distinguishes putty, thick enough for gouges and dings, from pore filler, which is too thin (Grain filler (pore filler)).
3. Nail holes in cabinet frames. Press "Color Putty" in with one finger and wipe it level with another. The cabinet-grade guide applies colour putty between finish coats.
4. Painted work. The linseed-paint article uses Durham's Rock Hard Water Putty as filler under paint, notes it will not accept stain, and sands the cured filler with a firm block.
5. Loose knots. Dribble epoxy into the gaps and tape the back of the knot so the epoxy cannot leak out, then sand flush after it sets (How to Stain Pine). Clear epoxy transmits the dark colour of the knot. If the epoxy cures milky-white, touch it up after you have dyed the wood and sealed it with shellac (Water-soluble dye stain, Alcohol and oil-soluble dye stain, Dewaxed shellac).
6. Re-sand every repair. Cabinet-Grade Finishing says dent, gouge and glue-seepage repairs need sanding again with at least the finest grit to level the repair or remove raised grain (Raising the grain).
7. Disguise afterwards. Where a repair shows, the glue-splotch article draws grain in with pigment in shellac, or pads colour on with lacquer (Shellac, Nitrocellulose lacquer).

Common problems

• Light patches under stain. Putty, glue or epoxy that does not absorb stain shows as a pale spot. Use a coloured putty, or colour the repair after staining as above.
• Epoxy and burn-in sticks. The sources opened for this guide say little more about epoxy repairs than the knot treatment above, and nothing about burn-in sticks or shellac sticks, so they are not described here.

Safety and environment

Epoxy and solvent putties need ventilation and gloves; read the product's safety data sheet. A hot iron or soldering iron can burn the wood and you. Wood dust: use extraction and a respirator.

Related

• Sanding schedule, Glue squeeze-out and common finish failures, Finishing veneers
• Finishing resinous and blotchy woods for knots and pitch
• Pre-stain conditioner and washcoat, Gel stain, Water-soluble dye stain, Alcohol and oil-soluble dye stain