Buzz
Just like proper sanding, careful sealing plays a crucial role in achieving great results when refinishing furniture. Sealer coats are applied between finishing steps to ensure uniform absorption of stains and finishes, prevent stain and filler bleeding, provide a solid base for the finish, and enhance the smoothness of the final surface. This guide will explore some effective methods for sealing wooden furniture.
Selecting the Right Sealer
For shellac, lacquer, and natural varnish finishes, the traditional sealer is a diluted white shellac. This basic sealer consists of 1 part white shellac (4-pound cut) mixed with 3 to 4 parts denatured alcohol. Shellac works well for most refinishing tasks, though it should not be used with polyurethane varnish or with water-based or NGR (non-grain-raising) stains.
When shellac isn’t an option, a commercial sanding sealer is an easy alternative. Sanding sealer dries quickly and provides an excellent sanding surface; it works well with varnish, shellac, or lacquer. If you plan to use polyurethane varnish, make sure to check the label carefully, as sanding sealer might not be compatible with polyurethane. Sealing is unnecessary when using a penetrating resin sealer as the finish.
For natural varnish or lacquer finishes, some experts recommend sealing the wood with a diluted version of the same finish. To create a natural varnish sealer, mix the varnish with turpentine or mineral spirits in equal parts. For a lacquer sealer, blend lacquer with lacquer thinner in equal quantities. These sealers cannot be used with shellac or polyurethane varnish.
Polyurethane varnish requires special attention. Always check the labels carefully before purchasing. Some polyurethane varnishes can be thinned with a specific thinner, and the manufacturer may suggest using thin coats of varnish as sealers. However, not all polyurethanes need sealers. If sealing is necessary before applying polyurethane, ensure the sealer is compatible with the varnish. Otherwise, use a penetrating resin sealer, which completes the finishing process, though polyurethane can still be applied over it for a smoother finish.
Sealing Process
Sealers should be applied in thin layers to avoid interfering with subsequent finishing steps. Before applying, ensure the wood is clean by removing any dust with a tack cloth. Apply the sealer with a clean brush, evenly and quickly along the wood grain. Ensure all surfaces are fully covered, paying extra attention to the end grain. Unsealed end grain will absorb stains and finishes more deeply than the rest of the wood.
Allow the sealer to dry completely—around two hours for thinned white shellac, or one hour for commercial sanding sealer. Then, lightly sand the surface with fine-grit sandpaper (7/0 grade). The wood should be very smooth, but be careful not to sand through the sealer. Use a tack cloth to remove any sanding residue.
When applying a finish directly to sanded wood, you may need to apply multiple coats of sealer to fully close the wood's pores. Allow the first coat to dry completely before adding another. Highly porous woods may require several coats of sealer to achieve full coverage.
If you're aiming for a long-lasting refinishing job and expect to see high-quality results for your investment, proper sealing is the key to achieving your desired outcome.
Publications International, Ltd.
