Wood Grain Filler 101: Get a Mirror-Like, Smooth Finish

By MWB-Team •  Updated: 06/05/23 • 

Filling the grain of wood is the easiest and fastest way of achieving a high gloss or mirror-like finish on open-grained wood species such as Oak, Ash, and Mahogany. Instead of using a finish to fill up pores, a grain filler is a better option, and it’s easier to apply. In this post, we’ll look at grain fillers, types, and how to use them.

Grain fillers use pigment-based colorants because the dye may fade over time, leaving pores lighter than the overall color of the wood. However, you can buy paste wood filler in different wood-tone colors or without color, usually called neutral.

Aqua Coat Clear Wood Grain Filler

Aqua Coat Clear Wood Grain Filler

Types of Grain Fillers

The type of grain filler is determined by the binder it uses to stick to wood. There are oil-based and water-based paste wood fillers available. Oil-based grain fillers have been around for a long time, while water-based grain fillers are fairly new.

Oil-Based Grain Fillers

This is the most common grain filler because solvent-based wood finishes are used more on high-end furniture worthy of being filled compared to water-based finishes. The fillers vary in drying time depending on the oil or varnish ratio used. However, most manufacturers will list the drying time of their fillers, but you’ll have to try to learn.

Oil-based grain fillers come in a number of neutral and different colors, so you can choose your color choice or mix to alter it slightly. Applying it over raw wood colors the wood and the pores, doing two jobs at once. If you apply it over sealed wood, it only covers the pores, which gives you more contrast and control over the appearance of the wood.

You can thin oil-based grain fillers with the two most common solvents: mineral spirits and naphtha. Mineral spirits evaporate more slowly than naphtha, so you’ll get more working time which is useful, especially for filling larger surfaces. Naphtha is great for smaller surfaces. You can also use both solvents to reach a middle ground. The choice of the thinner you use does not affect the curing time, just how long it takes before the filler becomes too hard to wipe off.

Water-Based Grain Fillers

Water-based paste wood grain fillers are fast drying, affecting their application and wait time before a finish. The difference from oil-based grain fillers is that they use water as a solvent and a compatible water-based resin or binder. However, water-based fillers’ fast drying time is the primary advantage.

Water-based grain filler can be applied with a brush or spray the filler onto larger surfaces and wipe the excess. However, you would get better results by using a squeegee or plastic spreader. Spread the filler while pressing it into the wood pores and remove the excess immediately.

Because it is fast drying, water-based grain filler is also easier to sand and takes a stain very well. You can apply the grain filler directly to the wood, remove the excess, and sand the rest after it dries. Once you’ve sanded it to a smooth finish, apply your desired stain to color both the filler and the wood. However, because different fillers take a stain differently, try it on a scrap piece of wood to be sure it performs as you like.

Most water-based grain fillers have a neutral color, which is a light tan or off-white color. However, there are some with colored pigment included. Some are transparent and help produce a richer clarity that is similar to oil-based grain fillers.

Applying Aqua Coat Grain Filler to Wood

Applying Aqua Coat Grain Filler to Wood

Applying Oil-Based Grain Filler

Although you can apply the filler to bare wood or sealed wood, sealing the wood before filling it can result in better contrast between the wood and filled pores. Sealing before filling will also give you more control over the filler application because you can wipe it easily and evenly over the sealed surface.

Applying a Water-Based Grain Filler

The difference between water-based and oil-based grain fillers is that water-based dries quickly. This leaves very little time to remove the excess. You can increase the working time by adding a propylene-glycol retarder or a thinner supplied by the manufacturer. Water-based grain filler is applied the same as oil-based, which is directly over bare wood and stained later or over a stain.

Before and After Applying Wood Grain Filler

Before and After Applying Wood Grain Filler

Grain Filler vs. Wood Filler

Wood grain filler is used to fill wood grain pores and is different from wood filler, which is used to fill larger cracks and openings in the wood. Grain fillers use a binder and a filler material which can be silica, clay, calcium carbonate, or silica microballoons. On the other end, most wood fillers are sawdust or wood dust suspended in a binder.

Wood fillers have a thicker consistency to fill larger cracks and avoid much shrinkage effectively. Grain fillers have a thinner consistency, making it easier to work into the wood grain. Most grain fillers are used on larger-grained woods such as oak and mahogany to get a smoother finish.

If you want to repair wood cracks and other voids, a wood filler is the best option. You can also check out our best stainable wood fillers that we have reviewed. Wood filler is also different from wood putty; check out this wood filler vs. wood putty guide for more information on that.

MWB-Team

Hello there! This is the Make Wood Better Team. Here, we share informative how-tos and guides focused on making wood better. Whether it's finishing wood, maintenance, or restoration, there's something on this website for you to learn and improve your skills.