To seal open grain wood, especially after staining, the key step is to apply a wash coat of finish.
Open-grain woods, such as oak, ash, mahogany, and walnut, have prominent pores or vessels that can absorb finish unevenly, leading to a blotchy appearance. Sealing the wood helps to fill or partially fill these pores, providing a more uniform surface for subsequent finish layers.
The Wash Coat Method
Based on common woodworking practices, including the reference provided, a recommended method for sealing open-grain wood after staining is to use a wash coat.
Here's how it generally works:
- Stain Application: Apply your chosen wood stain and allow it to dry completely according to the manufacturer's instructions.
- Apply a Wash Coat: Seal the wood with a wash coat of finish. A wash coat is essentially a thinned-down version of a clear finish.
- According to the reference, a wash coat is usually made by thinning lacquer or shellac with one part finish to three parts thinner.
- If you are using varnishes, you may have to experiment to find the right thinning ratio, although using aerosol shellac can be a convenient alternative.
- Allow to Dry: Let the wash coat dry thoroughly. The drying time will depend on the type of finish used and the environmental conditions.
- Light Sanding: Lightly sand the wash coat with fine-grit sandpaper (e.g., 320 or 400 grit). This helps to level the surface and prepare it for the next steps. Be careful not to sand through the stain or wash coat.
- Apply Topcoat(s): Proceed with applying your desired topcoat finish (e.g., varnish, polyurethane, lacquer).
Why Use a Wash Coat?
- Controls Stain Absorption: While you might have already stained, a wash coat helps to seal the surface and prevent subsequent coats of finish from soaking too deeply into the open grain, which could alter the color or create unevenness.
- Provides a Uniform Base: It creates a consistent base layer that helps subsequent topcoats build evenly and smoothly.
- Improves Adhesion: A wash coat can sometimes improve the adhesion between the stain and the final topcoat.
Wash Coat Mixing Ratios (General Examples)
The ratio provided in the reference is a good starting point, especially for lacquer and shellac.
| Finish Type | Finish : Thinner Ratio | Notes |
|---|---|---|
| Lacquer | 1 part : 3 parts | Use lacquer thinner |
| Shellac | 1 part : 3 parts | Use denatured alcohol |
| Varnish | Experimentation Needed | Use appropriate thinner (mineral spirits, etc.) |
| Shellac | N/A (Aerosol) | Convenient option |
Note: Always test your wash coat ratio and application on a scrap piece of the same wood before applying it to your project.
Sealing open grain wood with a wash coat is a standard technique to achieve a professional-looking and smooth finish, particularly after applying stain.
