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What is the Purpose of a Sanding Sealer

What is the Purpose of a Sanding Sealer

A sanding sealer is a type of coating that is used as a preparatory layer before applying a final finish on wood surfaces. The primary purpose of a sanding sealer is to seal the wood pores, fill in small imperfections, and create a smooth and even surface for the subsequent finish.

Here are the main purposes of using a sanding sealer:

  1. Sealing: Wood is a porous material that can absorb finishes unevenly, resulting in blotchy or uneven coloration. A sanding sealer helps seal the wood surface, reducing the absorbency and promoting a more uniform absorption of the final finish.
    • You might think that this process will prevent the stain from absorbing into the wood when staining wood.  However, once the sanding seal dries, you will want to sand it back just enough to expose the bare wood to the surface.  This will allow the stain to soak into the wood, but the sanding sealer has soaked in and filled the deeper pours, allowing you to get a more even stain color.
  2. Filling imperfections: Wood surfaces often have small pores, cracks, or uneven areas that can affect the appearance and smoothness of the final finish. Sanding sealer can fill these imperfections, creating a more flawless surface for the topcoat.
  3. Enhancing adhesion: Sanding sealers improve the adhesion of the final finish to the wood surface. The sealer provides a compatible and stable base for the topcoat, allowing it to adhere more effectively and minimize the risk of peeling or flaking.
  4. Time-saving sanding: Sanding sealers are designed to be sanded easily, allowing for quick and efficient surface preparation. The sealer’s formulation makes it softer and easier to sand than the final finish, reducing the time and effort required to achieve a smooth surface.
  5. Cost efficiency: Sanding sealers can help reduce the amount of expensive final finish required. Since the sealer fills imperfections and creates a smoother surface, the subsequent finish can be applied in thinner coats, saving material and costs.
  6. Grain Enhancement: Some sanding sealers contain colorants that can enhance the appearance of the wood grain, highlighting its natural beauty.

It’s important to note that not all wood projects require a sanding sealer. It depends on factors such as the type of wood, desired finish, and personal preference. However, using a sanding sealer can be beneficial when working with open-grained woods like oak or mahogany or when aiming for a particularly smooth and flawless finish.

The purpose of a sanding sealer is to prepare the surface of wood for the application of a topcoat finish, such as varnish, lacquer, or paint.  Sanding sealers are typically made from a combination of shellac, lacquer, or synthetic resins dissolved in a solvent. When applied to the wood, the sealer penetrates the surface and partially seals the wood fibers. This helps prevent the subsequent finish from being absorbed too deeply into the wood, resulting in a more even and controlled finish.

A hobby-friendly sanding sealer is Zinsser Sealcoat.

Some Common questions about sanding sealers

Does Sanding Sealer Go On Before or After the Stain

If you use a sanding sealer as blotch control to help even out the color on woods prone to botching when a stain is applied, you will want to put the sanding sealer on first.  This may seem counterintuitive as it will not allow the stain to penetrate the wood.  However, once the sanding sealer is dry, you will want to sand it back just far enough to expose the bare wood.  This will allow the stain to penetrate into the wood.

What has happened is when you apply the sanding sealer, the deeper, more thirsty grain soaks up the sanding sealer, sealing the deep pours.  When you sand it back, removing it from the surface, you are not removing it from the deep pours.  When you apply the stain in the next step, since the deep pours have been sealed, it prevents the stain from soaking into those deeper pours, thus allowing the stain to soak more evenly into the remaining wood, giving you a more even look.

With that said, many companies’ sanding sealers help with adhesion, so putting a sanding sealer on after you stain is recommended to help ensure your top coat will bond well.  A word of caution: Sanding sealers are designed to be soft and sanded easily, so when applying over a stain, you will only want to do an extremely light sanding at this point to knock down any dust nibs.  Any more aggressive sanding will sand into your stain color, ruining it.   However, if you have applied a coat of sanding sealer before staining and sanding back to bare wood, you will most likely have filled in most of the pours, so all you will need is a light sanding.

It is worth noting that if you are not staining the wood and are top coating with a clear coat, you do not need to sand back to bare wood.  Sand just enough to smooth out the seal coat.

How long do you leave the sanding sealer on?

This all depends on the dry time of the sealer you are using.  Most Shellac-based sealers will be dry and ready to sand back within 30 minutes, depending on temperature and humidity.  Some companies require a catalyst to be added to aid in drying and the sealer setting up properly.  Be sure to check the manufactures recommendations for the sealer you are using.  A surefire way to know if your sealer is dry is to test sand in an inconspicuous place.  If the sandpaper gums up, you want to let it dry more.  You are ready to sand if it creates a white powder and no gum on the paper.

How many coats of sanding sealer should be applied?

In most cases, you will need no more than one coat.  While building your project, it is a good idea to save a few scraps of wood to test your finish to be sure you are happy with the results.  If after one coat of sanding sealer is applied to your test piece and the wood is still blotchy when applying stain or top coat, a second coat may be needed.

When applying a finish, a good rule of thumb is to use scrap from the same project and test, observe, and then apply the finish on the final pieces.

Is Sanding Sealer The Same as Wood Conditioner?

Sanding sealer is not the same as wood conditioners or wood sealers.  Sanding sealer is formulated to fill in small voids and pours in the grain while creating a film to aid in top coat adhesion.  Wood conditioners or similar wood sealers are not designed to create a film but are designed to soak into the thirsty grain to prevent botching of the wood.

Which one should you use?  That all depends on the type of wood, stain, topcoat, and look you are going for.  That goes back to the rule of thumb to set on scrap before using it on the final project.

Can Sanding Sealer and Wood Conditioner be used on the same project?

Yes, if the sanding sealer was too aggressive and did not allow the stain to penetrate into the wood to get the color you wanted.  You can use a wood conditioner before staining to help control botching, then stain, then apply the sanding sealer, then top coat.  However, it is a good idea that you are using products that the manufacturer has tested to be compatible, or at the very least, you tested on scrap wood.

What are the cons of sanding sealer?

The primary con of sanding sealers is the added cost.  Keep in mind, though, that you have spent hours, maybe weeks, building the perfect piece.  Don’t ruin it with a pour finish.

Another con is aesthetics.  There is a saying one man’s blotch is another man’s figure.  One of the benefits of using a base finish is that it soaks deep into the wood, accentuating the figure in the grain and creating a warm and beautiful look.  Since sanding sealer soaks into the pores of the grain, it can reduce that grain-popping effect in the color.

Will sanding sealer raise the grain?

Sanding sealers will help minimize raised grain.  However, since you are sanding the sanding sealer, the raised grain will not be a concern in most cases since it will get sanded back.  If you use a water-based finish or stain, it is best practice to wet the wood with water first to raise the grain, then sand the wood to remove it before applying any sanding sealer, stain, or top coat.

I’m the owner of Benham Design Concepts, a mixed media art studio where I design and build custom furniture and other works of art using wood, glass, stone, and various metals.
In this blog, I talk about the art I create, my journey, and the things I learn along the way.

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