Sanding sealers are protective coatings that are designed to seal the pores in wood and prepare the surface for final finishing. They create a smooth, uniform surface that allows for easier sanding and improved adhesion of subsequent coats of finish. Sanding sealers have become an indispensable tool for woodworkers looking to achieve a flawless finish on their projects.
How Sanding Sealers Work
Sanding sealers work by penetrating into the wood grain and sealing up the pores. Unsealed porous woods like oak, ash, cherry, and mahogany absorb stains unevenly, resulting in a blotchy appearance. The varying porosity of the wood causes some areas to take up more stain while other areas resist absorbing the stain.
When a sanding sealer is applied first, it seals the wood evenly so the final stain or finish is taken up uniformly across the surface. This prevents uneven absorption and blotchiness. Sanding sealers also raise the wood grains, allowing you to sand the surface baby smooth before applying additional coats of finish.
Some of the key benefits of using a sanding sealer include:
- Seals the wood surface and evens out porosity differences
- Allows for uniform absorption of stains
- Prevents blotchiness in the final finish
- Raises wood grains so the surface can be sanded smooth
- Improves adhesion for subsequent coats of finish
- Reduces the number of finish coats required
Types of Sanding Sealers
There are several major types of sanding sealers to choose from:
Oil-Based Sanding Sealers
Traditional oil-based sealers contain drying oils like tung, linseed, or blends. They offer good pore penetration and bring out a warm, natural look in the woodgrain. Oil-based sealers dry slower than other types. They also contain solvents like mineral spirits for cleanup.
Water-Based Sanding Sealers
Water-based or acrylic sanding sealers provide faster dry times and easy cleanup with water. They raise the wood grain well but do not penetrate as deeply into the pores as oil-based sealers. Water-based sealers also impart a cooler tone to the wood.
Lacquer Sanding Sealers
Sanding sealers are also available in nitrocellulose lacquer formulations. Lacquer sealers dry extremely fast, but the fumes require proper ventilation. While lacquer sealers seal and raise the grains well, they do not penetrate as deeply into the wood pores as oil-based sealers.
Shellac-Based Sealers
Shellac-based sealers act like a primer coat to seal the wood. Shellac dries faster than oils and offers good pore penetration. However, shellac can be more difficult to sand smooth if multiple coats are applied.
Combination Sealers
Some proprietary blend sealers combine ingredients like oils, lacquers, urethanes, or varnishes. These are designed to provide the best qualities of each component in one product. Combination sealers offer a good balance of penetration, fast drying, and sandability.
When to Use a Sanding Sealer
Applying a sanding sealer is advisable on most bare wood surfaces before staining or finishing to prevent uneven blotching and improve the results. Certain wood types and applications that especially benefit from sanding sealers include:
- Open-pored woods like oak, ash, mahogany, walnut, cherry
- Exotic oily woods like teak, rosewood, and ebony
- Natural wood surfaces with color variations
- Turned wood objects like bowls, pens, rolling pins
- Wood furniture prior to staining
- Wood flooring before coating with polyurethane
- Wood cabinets before applying stain and varnish
- Wood doors before staining and coating with polyurethane
In general, a sanding sealer is a good idea whenever staining any porous bare wood prior to applying a protective clear finish. The sealer prevents blotchiness and prepares the wood for a smooth, consistent final finish.
How to Apply a Sanding Sealer
Applying a sanding sealer properly is important to get the full benefits. Follow these steps:
Surface Preparation
- Ensure the wood surface is clean, dry, and free of wax, grease, or contaminants
- Sand the wood with 120-150 grit sandpaper to remove mill marks and imperfections
- Dust off the surface and wipe it down with a tack cloth
Applying the Sealer
- Shake or stir the sealer thoroughly before applying
- Apply a thin, even coat across the wood grain using a brush or cloth
- Let the sealer penetrate for 5-10 minutes before wiping off any excess
- Allow the sealer to dry per the manufacturer’s recommendation
Sanding and Second Coat
- Once dry, sand lightly with 220-320 grit sandpaper to smooth any raised grains
- Remove dust and apply a second thin coat of sealer for maximum grain sealing
- Let the second coat dry fully, then sand again with fine 320-400 grit sandpaper
Finish Coats
- Ensure the surface is smooth and dust-free
- Apply desired stains, paints, varnishes, oils, or other finishes as directed
- The sealed surface will allow for more consistent, uniform absorption of finishes
Be sure to read and follow the specific application directions on the sealer product you are using as they can vary. Proper application is key to getting the full benefits of grain sealing and pore penetration before applying subsequent coats.
Applying Stain Over a Sanding Sealer
One of the main benefits of using a sanding sealer is it allows stains to penetrate the wood more evenly. Follow these tips when applying stain over a sealed surface:
- Make sure the sanding sealer has fully dried before staining
- Gently sand the sealed surface with 320-400 grit sandpaper before staining
- Use a gel stain or non-penetrating stain which sits on the surface rather than absorbing into the pores
- Apply a thin coat of stain using a rag or foam brush and immediately wipe off any excess
- Allow the stain to dry per the directions, then apply finish coats
The sanding sealer prevents the stain from penetrating unevenly for a more uniform, consistent color. Always test on scrap wood first when applying over sealers as absorption may be less than on unsealed wood.
Advantages of Sanding Sealers
Using a quality sanding sealer provides many advantages for finishing bare wood:
- Evens out porosity differences in the wood grain
- Allows for uniform penetration and color of stains
- Prevents blotchy, uneven stain absorption
- Seals the surface so finish coats build evenly
- Allows for easier sanding by raising the wood grains
- Provides a smoother base for applying subsequent finishes
- Enhances adhesion of varnish, paint, oils, and polyurethane
- Reduces the number of finish coats required
- Brings out a rich, warm tone from the natural wood
Disadvantages of Sanding Sealers
While sanding sealers provide many benefits, there are a few potential disadvantages to consider:
- Adds an extra step before staining and finishing
- Sealers require proper sanding between coats
- Oil-based sealers add drying time compared to water-based types
- Fumes may require proper ventilation
- Too many coats can lead to adhesion or sanding issues
- May slightly reduce penetration of some penetrating finish oils
However, the advantages almost always outweigh any disadvantages when finishing porous or uneven woods.
Common Questions About Sanding Sealers
Do you have to use a sanding sealer?
While a sanding sealer is not absolutely mandatory, it is highly recommended for most bare wood surfaces. Sanding sealers are useful on a wide variety of woods prior to finishing to prevent blotchiness, provide grain filling, improve sanding, and enhance finish adhesion. Many experienced woodworkers would not consider staining or finishing porous woods like oak or ash without first applying a sanding sealer.
Should you sand between coats of sealer?
Yes, it is advisable to lightly sand between coats of sanding sealer. This ensures each fresh coat bonds well and provides smoothing of any raised wood grain. Use fine 220-320 grit sandpaper and wipe away dust before recoating. Gentle sanding also prevents build up and improves adhesion.
How many coats of sealer should you apply?
Typically, two thin seal coats are ideal for sealing the wood properly before finishing. The first coat penetrates and seals the deeper pores while the second evens out the surface. Sanding between coats helps smooth the surface. More than two coats may lead to adhesion problems when finishing.
Can you use polyurethane instead of sanding sealer?
While you can apply polyurethane without using a dedicated sanding sealer first, it is not ideal. Polyurethane does not penetrate the pores as well, so staining may still appear blotchy. The sanding sealer provides superior sealing and grain raising for a smoother finish. Using it under polyurethane improves the final result.
What sheen of sealer should you use?
Sanding sealers come in different sheens from flat/matte to semi-gloss and gloss. Flat or satin sealers are preferable as they allow you to achieve the desired sheen with your final finish coat. Gloss sealers can inhibit full penetration of stain and finishes. Satin is a good compromise that provides some sealing without too much sheen.
Tips for Using Sanding Sealers Effectively
To get the best results from sanding sealers:
- Shake or stir the sealer before and during application for consistent results
- Apply thin coats and wipe off any excess for penetration into the pores
- Allow proper drying time as indicated on the product instructions
- Always sand lightly between coats with fine sandpaper
- Work in good ventilation and wear protective equipment like gloves and respirators
- Test on scrap wood pieces first to ensure proper compatibility with your planned finishes
- Store oil-based sealers away from any ignition sources due to combustibility
- Clean brushes and tools with the appropriate solvents after use
- Dispose of oily rags properly to prevent potential spontaneous combustion
Using the right sanding sealer for your project along with proper application techniques will provide superior wood sealing and preparation for an ultra-smooth finish.
Benefits of Using a Sanding Sealer Before Applying Polyurethane
Polyurethane is a popular protective clear finish for wood surfaces. Applying a sanding sealer first provides multiple benefits when using polyurethane:
- Seals porous wood evenly so poly absorbs uniformly
- Allows polyurethane to build to a smooth, consistent film
- Prevents blotchiness and uneven sheen in the cured poly
- Permits easier sanding between polyurethane coats
- Raises the wood grains for a super smooth finish
- Enhances adhesion so poly bonds tightly to the wood
- Reduces number of poly coats needed by sealing the surface
- Provides a base layer that lets poly dry harder
Sanding sealers enhance the performance of polyurethane finishes on wood surfaces like floors, furniture, cabinets, and more. The sealer regulates absorption and improves poly flow and leveling. Just be sure to lightly sand between each coating. Applying this simple first step will result in a clearer, more durable polyurethane finish.
Safety Tips When Using Sanding Sealers
While sanding sealers improve wood finishing, they do contain chemicals that demand proper safety:
- Work in a well-ventilated area to prevent buildup of toxic fumes
- Wear protective gloves, goggles, and a respirator or mask
- Avoid exposure to liquid sealers by working carefully
- Store oil-based sealers away from ignition sources due to flammability
- Dispose of used rags properly as they can combust spontaneously
- Keep sealers locked away out of reach of children
- Oil-based sealers are combustible so avoid open flames or sparks
- Follow all safety directions listed on the sealer labels
- Clean up spills rapidly with appropriate solvents
- Wash skin and eyes thoroughly in case of any contact with sealers
Exercising common sense safety measures allows you to use sanding sealers safely and get the superior finishing results they provide.
Frequently Asked Questions About Sanding Sealers
What are some top sanding sealer brands?
Some of the leading sanding sealer brands include Minwax, Varathane, Zinsser, General Finishes, Krylon, Rust-Oleum, and Defy. These companies offer trusted oil, water-based, and shellac sanding sealers.
How long does it take sanding sealer to dry?
Drying times vary based on the sealer type. Oil-based sealers take 6-8 hours or longer to dry while water-based sealers dry in under an hour. Shellac dries fastest in about 20-30 minutes. Always follow manufacturer directions for drying between coats.
Can you use wood conditioner instead of sanding sealer?
Wood conditioners help reduce blotchiness like sanding sealers but do not seal the wood completely. They also don’t build a surface layer for sanding smooth as well as dedicated sanding sealers. Using a sanding sealer provides superior results.
What grit sandpaper should you use with sanding sealer?
Use 120-150 grit to sand wood initially before applying sealer. Sand between coats with 220-320 grit for smoothness without removing sealer from the pores. Finish sand with 320-400 grit. Remember to remove dust before recoating.
How do you thin sanding sealer?
Oil-based sealers can be thinned with mineral spirits up to 10% by volume. For water-based sealers use water, up to 10% as well. Thinning allows for better penetration into dense woods. Always thin gradually while testing on scraps to avoid over-thinning.
Conclusion
Sanding sealers are essential tools for preparing bare wood and getting professional finishing results. By evening out porosity, preventing blotches, building a smooth base, and allowing for easier staining and topcoating, sanding sealers help woodworkers achieve flawless finishes. Just be sure to choose the right sealer for your project, apply it properly, and sand thoroughly between coats. Employing a quality sanding sealer as part of your finishing process will take your wood projects to the next level.