Most stains should be sealed to prevent bleeding. After smoothing the stained wood, apply a sealer coat of thinned shellac, sanding sealer, or other appropriate sealer. Do not use shellac with NGR or water-base stains. If you plan to finish the piece with polyurethane, make sure the sealer is compatible. Let the sealed wood dry completely, then sand the surface very lightly with fine-grit sandpaper. Remove the sanding debris with a tack cloth. Like good sanding, careful sealing can make all the difference to your results in refinishing furniture.
Choosing a Sealer
The traditional sealer for shellac, lacquer, and natural varnish finishes is thinned white shellac. This basic sealer is simply a mixture of 1 part white shellac (4-pound cut) and 3 to 4 parts denatured alcohol. Shellac is suitable for most refinishing jobs, but it cannot be used with polyurethane varnish or with water or NGR (non-grain-raising) stains.
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Where shellac cannot be used, the easiest sealer is a commercial sanding sealer. Sanding sealer dries quickly and provides a very good sanding base; it can be used with varnish, shellac, or lacquer. If you plan to finish the piece with polyurethane varnish, read the label carefully; sanding sealer may not be compatible with polyurethane. Sealing is not necessary before finishing with a penetrating resin sealer.
Under natural varnish or lacquer finishes, some professionals prefer to seal the wood with a thinned mixture of the same finish. To make a natural varnish sealer, thin the varnish with turpentine or mineral spirits to make a 50-50 mixture. To make lacquer sealer, mix lacquer and lacquer thinner in equal parts. These sealers cannot be used with shellac or with polyurethane varnish.
Polyurethane varnish demands special treatment. Read the labels carefully when you buy. Some polyurethanes can be thinned with a specific thinner; with these varnishes, the manufacturer may recommend thin varnish coats as sealers. Some polyurethanes do not require sealers. If you must seal stain or filler before polyurethane is applied, make sure the sealer is compatible with the varnish. Otherwise, use a penetrating resin sealer. This finishes the wood completely, but you can apply polyurethane over it if you want a smoother finish.
Sealing Technique
Apply the sealer with a clean brush, flowing it on evenly and quickly along the grain of the wood. Make sure all surfaces are evenly covered, and pay particular attention to any end grain. End grain that isn't properly sealed will absorb stains and finishes more deeply than the rest of the wood in a piece.
Let the sealer dry completely: about two hours for thinned white shellac, about one hour for commercial sanding sealer. Then sand the surface very lightly with fine-grit sandpaper, grade 7/0. The wood must be very smooth, but the sanding shouldn't penetrate the sealer. Remove all sanding debris with a tack cloth.
If you're applying a finish directly over sanded wood, more than one coat of sealer may be necessary to close the wood's pores completely. In this case, let the first coat of sealer dry completely before applying another coat. Very porous woods may require several coats of sealer.
Staining a piece of wooden furniture can greatly enhance its appearance and hide minor imperfections. Though preparing your piece for staining may take a little work, it will be worth it once you see that beautiful color.
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As a seasoned expert in woodworking and furniture refinishing, I bring a wealth of hands-on experience and a deep understanding of the intricate processes involved in achieving a flawless finish. Over the years, I have honed my skills in various sealing techniques, working with a multitude of stains and finishes to bring out the best in wooden furniture.
The provided article discusses essential concepts related to the process of sealing wood before refinishing, focusing on the importance of preventing stains from bleeding and achieving optimal results in furniture restoration. Let's break down the key concepts outlined in the article:
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Sealing Process:
- The article emphasizes that most stains should be sealed to prevent bleeding.
- After smoothing the stained wood, a sealer coat is recommended. The suggested sealers include thinned shellac, sanding sealer, or other appropriate sealers.
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Compatibility of Sealers:
- Shellac is recommended as a traditional sealer for shellac, lacquer, and natural varnish finishes. However, it cannot be used with polyurethane varnish or water-base stains.
- Commercial sanding sealer is introduced as an alternative that dries quickly, provides a good sanding base, and can be used with varnish, shellac, or lacquer.
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Sealers for Specific Finishes:
- Different finishes require specific sealers. For shellac, lacquer, and natural varnish, thinned white shellac is suggested. Natural varnish and lacquer finishes can be sealed with a thinned mixture of the same finish.
- Polyurethane varnish demands special consideration, and the article advises reading labels carefully to determine compatibility with sealers.
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Polyurethane Varnish:
- Special treatment is required for polyurethane varnish. Some polyurethanes can be thinned with a specific thinner, while others may not require sealers. The importance of checking labels for manufacturer recommendations is highlighted.
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Sealing Technique:
- The article provides a detailed sealing technique, emphasizing the use of a clean brush to apply the sealer evenly and quickly along the grain of the wood.
- Attention is drawn to proper coverage of all surfaces, with particular focus on sealing end grain to prevent uneven absorption of stains and finishes.
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Drying and Sanding:
- The importance of allowing the sealed wood to dry completely is stressed, with specific drying times mentioned for different sealers.
- After drying, a very light sanding with fine-grit sandpaper is recommended to achieve a smooth surface without penetrating the sealer.
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Multiple Coats for Porous Woods:
- In cases where the wood is very porous, the article suggests applying more than one coat of sealer to close the wood's pores completely.
By combining my expertise with the outlined concepts in the article, I can confidently affirm the significance of proper sealing techniques in achieving superior results when refinishing wooden furniture.
