TOOL
Sanding sealer
The first coat that stops the wood drinking the finish.
| Type | Nitrocellulose or vinyl sealer |
|---|---|
| Application | Spray or brush, one or two thin coats |
| Dry time | 30 – 60 minutes before sanding |
| Purpose | Seal pores, raise grain, key the surface |
| Sand back | 320 – 400 grit, lightly |
| Compatibility | Matched to the topcoat system |
| Coats | One or two thin coats |
|---|---|
| Sanding | Light — the aim is to flatten, not to remove the sealer |
| Grain raising | Dampen first for a smoother result |
| Humidity | Under 60 percent, as for the topcoat |
| Topcoat | Apply within the recoat window |
| Price band | Low |
Sanding sealer is a thin, fast-drying coat applied before the main finish. It soaks into the open pores of the wood, hardens, and stops the topcoats sinking in and leaving a patchy, starved look. It also raises the grain so it can be sanded back flat.
It is not a finish in its own right. Its job is to seal, to raise the grain, and to give the first sanding something to cut — after which the real finish goes on over a flat, sealed surface.
At this stage
Sealer goes on before any colour or topcoat, after the surface has been sanded to final grit and any grain filler has been applied and levelled.
Suits these instruments
- Steel-string acoustic
- Electric
- Archtop
- Bass
Works with
- Nitrocellulose lacquer
- Grain filler
- Spray equipment
- Sanding blocks
- Sealer carries the same solvent hazards as the topcoat. Extraction and an organic-vapour respirator.
- Sanding sealer dust is fine and flammable. Keep the work area clean and do not let dust build up around ignition sources.
Working notes
- Dampen the wood and sand back before sealing to cut the raised grain once, cleanly.
- Do not sand through the sealer — a bare patch drinks the topcoat and shows as a dull spot.
- Match the sealer to the topcoat system. A mismatched pair can blister.
- A thin sealer coat is better than a thick one. Thick sealer cracks.
Related
Nitrocellulose lacquer
The traditional finish: thin, clear, and easy to repair.
French polish
A shellac film applied by hand, one thin layer at a time.
Glue
Three glues, three jobs, and none of them interchangeable.
Clamps
Enough of them, and enough reach.