What Is Wood Grain Filler? (All You Need to Know)

In Tips, Tools by Jamie P.

The grain on wood is what gives it a unique appearance and it’s often the biggest selling point. Wood with a nice unique grain doesn’t come cheap, but sometimes, the grain can be an issue. Open grains take in a lot of moisture, making it hard to finish them. They also stop you from getting a completely smooth surface when painting or staining. Wood grain filler can rectify that problem.

This article will explain what wood grain filler is, what the different types are, and how you can use it. There will be some product recommendations included too, so you can start using wood grain filler for your next project.

What Is Wood Grain Filler?

Wood grain filler is a specific type of filler designed to give you a smooth finish on wood by filling the pores in the grain of the wood. It is sometimes referred to as pore filler or paste wood filler. It tends to be used on wood types with a very open grain, like walnut, oak, or mahogany. The open grain soaks up a lot of moisture, so when varnishing or oiling, it can be difficult to get a nice smooth finish. A wood grain filler helps to get around this problem.

Is Wood Grain Filler Necessary?

Wood grain filler is not always necessary, it depends what type of wood you are using and what finish you are looking for. If you are using a wood with a tight grain, a coat of oil or varnish will soak in and fill the pores quite easily, so you get a smooth surface. However, if you are using open-grained wood and you want it to be smooth, wood grain filler is the best way.

That said, you don’t always need a completely smooth finish. It’s desirable if you are finishing furniture, for example. But you don’t need to bother if you are finishing more practical items that are not handled regularly, especially exterior projects. I don’t often use a grain filler on my furniture projects because I don’t mind the natural grain coming through my finished surface.

What is Wood Grain Filler Made of?

Different brands of wood grain filler have their own composition, but they all contain the same basic elements; a binder, a bulking agent, and a solvent. The binder is the finish that you want to apply to the wood. The bulking agent is there to fill big gaps, and the solvent is a vehicle for the other components. When the grain filler dries, the solvent will evaporate, leaving the other substances bonded to the wood.

The binder can be oil-based or water-based and the type of solvent used is dependent on the binder. The bulking agent is usually silica because it doesn’t expand and contract when exposed to humidity and temperature changes. You may also see quartz powder, talc, or wood flour used as a bulking agent.

Young carpenter in work clothes and face mask using wood grain filler in finishing work for console table .

Water-Based vs Oil-Based Wood Grain Filler?

Water-based and oil-based wood grain fillers work in the same way, but there are some key differences you should be aware of.

Oil-based wood grain filler uses a blend of oils and varnishes as the binding agent. These are the same kinds of oils and varnishes that you find in standard wood finishes. The oil helps to add moisture to the wood and give it a rich look, while also filling in the grain. The solvent in these fillers is usually mineral spirits or something similar. Oil-based wood grain fillers have been around for a long time and they’re the preferred method for a lot of people.

However, water-based products are fast gaining popularity, mainly because they’re quicker and easier to use. The binding agent in water-based products is usually acrylic or urethane and there is no need for mineral spirits as a solvent, they just use water. So, you have fewer chemicals that give off strong fumes when using a water-based product. They dry a lot faster and they’re easy to clean up with soap and water too.

In general, water-based grain fillers are the way to go because they are simpler to use and you’ll get the same results. The only exception to this is when working in humid conditions. Water-based grain fillers don’t do well with high humidity and the finish can be quite patchy, so keep this in mind.

What’s the Difference Between Grain Filler and Wood Filler?

The main difference between grain filler and wood filler is that the latter is used for repairs. A wood filler is there for filling holes and cracks or, in some cases, replacing large pieces of wood that are missing. If you have wooden window frames, for example, you would use a filler to fix cracks and replace any sections that have rotted. A grain filler, on the other hand, is not suitable for these kinds of repairs, it is used for smoothing over open grained wood.

The consistency is the easiest way to tell the two apart. Wood filler is thicker because it needs to fill holes, while grain filler has a thinner consistency because it needs to soak into the wood and fill the pores. Usually, grain filler is the same consistency as pancake batter and wood filler is more of a paste.

Wood fillers are available in oil-based and water-based options just like grain filler, and the basic components are often very similar. There are also separate products for interior and exterior use. But even though there are similarities, grain filler and wood filler should not be used interchangeably.

When is Grain Filler Often Used?

Grain filler is used for any project that requires a nice smooth finish. The grain filler is applied first to fill the pores and make the surface completely smooth. Then, the normal finish is applied over the top (oil or varnish, etc). This gives a mirror finish that cannot otherwise be achieved without the grain filler.

It is most commonly used for furniture projects, especially tables and desks where a nice mirror finish is needed. People also use wood grain filler on old cabinets so they can paint them and get a smooth finish.

How to Apply Wood Grain Filler? (Step by Step)

Every product is slightly different, but you can follow these basic steps to apply wood grain filler to a piece of furniture.

1. Clean and sand the wood

The wood needs to be completely clean before you apply your grain filler. If the wood has been finished in the past, you need to remove all of the old varnish or paint before you get started. If the filler cannot get into the grain, it won’t fill it.

The wood needs to be sanded to expose the grain and open up the pores, so the grain filler can get right in there when you apply it. Sand your piece of furniture all over with 80 grit sandpaper to prepare it for filling, then give it a good wipe down with a damp cloth to remove any dust.

2. Make repairs (if necessary)

If you are working with an old piece of furniture, you may need to make some repairs. Use a wood filler (not grain filler) to fill any cracks or holes in the wood. Make sure you choose a filler that can be sanded and varnished over.

When it has fully dried, sand the excess off so you have a smooth finish again. Give the wood another wipe with a damp cloth to get rid of dust and then let it dry.

3. Apply wood grain filler

Now, it’s time to apply your wood grain filler. Depending on the product you buy, you may need to mix the filler. If it already has a fairly loose consistency and will soak into the wood easily, you can use it right away. But thicker products may need to be mixed with some water to loosen them up. Check the manufacturer’s guidelines to ensure that you get the right amount of filler and the right consistency. If you apply too much, it can be hard to get an even finish, but if you don’t apply enough, you will get lots of small cracks and gaps.

There are a number of ways to apply wood grain filler. Most people use a putty knife or a small trowel to scrape it over the surface of the wood. Make sure that you push the grain filler down into the pores as you do this. You can then wipe off the excess, ensuring that all of the grain is filled.

Alternatively, if you loosen up the grain filler with some water, you can apply it with a paintbrush and let it soak into the wood. Usually, the advice is to work with the grain when applying anything to wood, but in this case, do the opposite. If you work against the grain, you will get deeper into the pores of the wood. Bear in mind that the drying times will be longer with this method, but it is useful for more intricate pieces of furniture like chairs that have a lot of difficult to reach areas.

When applying the wood grain filler, don’t worry too much about having a smooth surface because that will be dealt with in the next step. The most important thing is that you fill all of the deep pores in the wood and there are no gaps. Once you are confident you have done this and you have wiped off the excess, let it dry.

The drying times vary between products and water-based grain fillers will dry much faster. Always check the recommended drying times and stick to them for the best results.

4. Sand to a smooth surface

When the filler is dry, you can sand it down so it is level with the wood and you have a nice smooth surface. You don’t want to ruin the nice surface you have created, so use a fine sandpaper (220 grit) to gently smooth the surface. This may take some time, so be patient with it for the best results. If you try to rush it by using coarse sandpaper, you won’t get the glass-like finish once you apply varnish or oil.

Give the wood a wipe down to clear away the dust and then let it dry.

5. Finish the wood

Now that you have filled all of the pores in the wood, you can apply your finish of choice to give you the mirror finish. The type of finish you choose and how it is applied all depends on your preferences. Oils and varnishes work well, but you can also apply water-based clear coats like spar urethane over the top. This is especially good for exterior projects that need protection from the elements.

What are the Best Wood Grain Fillers?

1. Aqua Coat

Aqua Coat is one of the most popular wood grain fillers, and for good reason. It’s a water-based, eco-friendly filler that gives excellent results and it’s easy to use, even if you don’t have any experience with grain fillers.

It’s best applied with a putty knife, scraping it over the surface and pushing it into the pores. Be careful when wiping off the excess because you can pull it out of the pores if you are too rough with it. You may need to go over a few times, leaving it for around an hour in between each pass, so you can get every single gap.

The finish is completely clear, so it’s ideal for any project, no matter what you want to put over the top. However, you can also mix it with any water-soluble dyes and pigments you like, so you can get the perfect base color. This will save you time when finishing the wood because you probably will not need as many coats. As far as all-purpose wood grain fillers go, Aqua Coat is definitely one of the best.

2. DAP Premium Wood Filler

If you have some old furniture that you want to bring back to life, DAP Premium Wood Filler is what you need. This is an excellent 3-in-1 product that acts as a standard wood filler and a sealer coat, as well as a grain filler. The texture of it is like a standard wood filler, but if you loosen it with water and brush it into the wood, it acts as a good quality grain sealer. So, you can use it to repair any damage to furniture before then watering it down and sealing the wood grain.

Once dry, it is completely sandable, paintable, and stainable. The normal finish is white, but again, you can mix almost all water-soluble pigments and dyes into it to get the desired color.

The DAP Premium Wood Filler is great for use on old furniture because it saves you having to buy multiple products to repair the wood and fill the grain.

3. Goodfilla Water-Based Wood and Grain Filler

Goodfilla Water-Based Filler is a great multipurpose wood and grain filler that can be used straight out of the tub with a trowel or putty knife. It fills the grain nicely and gives you a good surface for painting and staining. It is also the only grain filler you can find that doesn’t use acrylic or latex. The main benefit of this is that it doesn’t harden as quickly when left in the tub, giving it an almost unlimited shelf life. If it does get a bit hard, you can add a bit of water and mix it up again and it will work perfectly.

The only downside with this one is that it does have a strong smell. However, if you use it in a well-ventilated area, that will soon fade.

Can You Stain Over Wood Grain Filler?

Yes, wood grain filler is designed to prepare the wood before you add another finish over the top, usually stain or oil. Almost all water-based wood grain fillers will take stain well. However, you should still double-check the packaging beforehand. The grain filler also makes the surface less porous, so you may need more coats of stain to get the desired color.

Can You Paint Over Wood Grain Filler?

Yes, in fact, people often use wood grain filler to coat wood before painting. Using the filler stops the grain of the wood from showing through once you have painted. This can be achieved with paint alone but you need to apply a good primer and lots of coats. A wood grain filler is the faster and cheaper option.

Is it Possible that a Water-Based Clear Coat Could Raise the Grain Even After Grain Filler?

It is less likely that a water-based clear coat will raise the grain after it has been filled, but it still happens. Although less moisture can soak into the pores of the wood after grain filler, grain raise can be a problem.

If you are particularly concerned about it, the best way to avoid it is to raise the grain before you apply the filler. Start by sanding the wood down and then wetting it with a sponge. Leave it overnight to let the grain raise, and then sand it down again. Once it has raised once, it will not raise anywhere near as much again. If you then apply the grain filler after doing this, you shouldn’t have any problems.

What’s the Best Clear Coat Protection After Using Grain Filler?

Urethane and polyurethane are usually the best clear coats to use after applying grain filler. They give excellent protection against the elements and you will get a nice glossy finish. You can also get satin and semi-satin options, if necessary. For any exterior projects or furniture that is likely to see a lot of spills and wear and tear, like tables, these tough clear coats are excellent. If you need a completely waterproof finish, epoxy-based clear coats are the way to go.

Wood Grain Filler FAQs

Can You Buy Water-Based Wood Grain Filler?

Yes, many modern wood grain fillers are water-based these days. They’re an excellent choice because they don’t contain any VOCs and they dry quickly. They are also very simple to clean up with soap and water.

Can You Buy Oil-Based Wood Grain Filler?

Yes, oil-based wood grain fillers are still available. However, I would recommend going with water-based options, in most cases. If you are very concerned about grain raise, an oil-based product could be better but overall, they’re just harder to use and take longer to dry.

Is Wood Grain Filler Toxic?

Some oil-based wood grain fillers contain strong solvents, so they need to be used in a well-ventilated area. But if you are using a water-based product, you don’t need to worry. The filler will be covered with another finish, so you don’t need to worry about issues with toxicity.

How Long Does Wood Grain Filler Take to Dry?

This depends on the product, but a good quality water-based grain filler like Aqua Coat takes around 30-45 minutes to dry before you can put on a new coat. You should give it a little longer before sanding it down.

Oil-based grain filler, on the other hand, will take considerably longer. You can expect it to take upwards of 4 hours and if it is particularly humid, this will extend the drying times a lot.

Can You Make Your Own Grain Filler?

If you want to, it is possible to make your own solution to fill the pores in the wood. A mixture of wood oil (Danish oil works particularly well) and sanding dust will pack into the pores and harden, giving you a similar effect to grain filler.

To achieve this, pour a good amount of oil onto the wood and then use 100 grit sandpaper to sand the surface and produce the dust. Then, take a cloth and then wipe this mixture over the surface, packing it into the pores of the wood. You can let it dry overnight and repeat the process the next day, adding more oil if needed. After doing this 2 or 3 times, the pores should all be filled.

This is a simple method but it does require more time and effort on your part. If you want an easier job, just buy some grain filler to do the hard work for you.

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