Wood Filler, Material for Filling the Wood Pores and Grain

Wood filler is a finishing material used to fill wood grain and pores. Wood filler has a low shrinkage value so that it will fill the pores and grain and stay in it when it is applied. It will fill the wood texture and close the pores and grain with small shrinkage when dry.

The function of fillers

• Fills pores and grains

Filler is purposed to fill the wood grains and pores and make the wood surface more even when it is layered by coating it. The filler helps to cover the pores and grain and prevent the coating from soaking into the pores and grain. Normally the pores and grain of the wood will absorb the coating layered on it. The filler application will reduce the layer coating needed to make the even finishing layer, especially when you build the closed pores finish. If you use the NC system, the filler is absolutely necessary to make a close-pore finish. If the thermosetting paint (PU, Melamine, UV coating) then filler application will reduce the layers of sealer or top coat needed to create a close pore finish.

• Coloring pores and grain

While filler fills the wood pores and grains, it is also coloring the grain and pores. For this purpose, the filler is available in various colors, which can be chosen according to the color and appearance of the finishing built. The coloration of the filler is special because it only stays and colors inside the pores and grains. The filler color can be made the same as or according to the finishing color to produce the calm appearance. The filler will reduce the appearance of pores and wood grain. On the other hand, the filler color can be different from the finishing color if you want a finish that enhances the grain and pore pattern of the wood. Filler can also be chosen in contrast with the finishing color to produce a contrasting and lively impression of the wood grain and pores.

wood filler application

Types of fillers

Filler is made from a mixture of bulk agent (a material that has a low shrinkage value), resin as a binder, pigment as a coloring agent, and some solvent as a thinner. According to the resin mixture added, there are several types of filler, such as NC filler, acrylic filler, alkyd filler, epoxy filler, etc. However, to make things simple in application, fillers can be classified as: water-based filler, solvent-base filler, wiping filler, and UV filler.

•  Water base filler

Water-base filler is a filler that uses water as a main thinner. This filler is very popular in the wood finishing. It is very easy to be used with pretty good results. This water-based filler is applied to raw wood using a putty knife or roller. Water base filler dries quickly and is easy to be sanded then go to the next process, i.e., stain, sealer, or paint application. The good-quality water-base filler can absorb the color of the stain applied to it. Then the filler can get stained and colored as the stain color to make the finishing result life and nice looking. This water base filler can be coated with other types of coating, such as water base, nc, pu, or melamine. For large-scale production, the water base filler can be applied using a roller machine that is equipped with a hot oven and sanding machine. The panels enter the machine to be filled, dried, and sanded. Once the panels are out of the machine, they are already filled and sanded and ready for the next finishing process.

• Solvent base filler

Solvent-base filler uses solvent as a thinner. This filler dries quickly and is easy to apply with good results. Solvent base filler is generally applied manually by filler knife or putty knife. The use of solvent makes the filler dry fast and less sensitive to the environmental condition. A good sanding process is needed to clean the remains of filler stuck to the surface. 

•  UV filler

UV filler is a filler that uses a process such as UV coating. This filler requires a UV light oven to dry and is usually used in the UV system finishing or flat line finishing process. The UV filler is applied in a series of UV coating machines. With this system, the wood is entering a series of machine and undergoes a series of finishing process with a perfect finish when it is out from the machine

• Wiping filler

Wiping filler is a filler that is applied by wiping. This filler is applied by pouring or brushing it onto the surface and then wiped evenly to cover the entire surface. Wiping is needed to clean the filler on the surface and led the filler inside the pores and grain only. This filler is designed to be cleaned by wiping and does not require sanding. Steel wool or scotch brite can be used to make better cleaning on the surface if necessary

How to apply filler

Filler is a very thick material; therefore, it cannot be sprayed. The best way to apply filler is to pour it onto the surface and then spread it and squeeze it evenly over the entire surface. The tools for filler manual application are knife, cloth, roller, or paper. For large-scale production, filler application can be done using a roller machine, which will lay the filler on the surface and at the same time press it into the pores and grain. This roller machine is the machine to apply the water base or UV fillers, where the processes are run and controlled by the machine. 

Things that need to be considered when using fillers

•  Type of filler

There are several types of filler, and each has its own specifications and application method. Make sure you know the types of filler you are using and know how to use it correctly. Read the PDS and make sure you apply according to the specifications.

• Color and appearance of the filler

Filler has several colors to be chosen according to the desired finishing color and appearance. Make sure you know the finishing color you want and choose the right filler according to the finishing look and color.

• Filler cleaning

Filler is a material to fill pores and grains; therefore, this filler should be left inside the grain and pores only. Filler does not have enough binder; the filler that stays on the surface won’t stick to the surface and is easy to come off. Filler that is smeared on the surface will make the finishing look ugly and also potentially cause adhesion problems. Therefore, make sure the filler is cleaned well and only left inside the pore and grain. Make sure there is no filler left on the surface.

• Drying of filler

After application, the filler must be completely dry before continuing with the next finishing process. Filler is a thick and solid material; it generally requires quite a long drying time, but it needed to be fulfilled. The undried filler will cause many kinds of problems, such as color and look problems, adhesion problems, and also bubble and pinhole problems.

• Make sure the wood filler fills all the pores and grain perfectly.

To get maximum benefits, the filler must fill all the wood grains and pores perfectly. The missing area of the filler application will create finishing problems because of the uneven condition of the surface. Imperfect application of filler does not help speed up the finishing process, but it will lead to many problems, such as bubbles or pinholes, which are not easy to solve. For wood with big and deep pores, it may need two-time filler application or even more to ensure that the filler fills the pores and grains perfectly.

• Understand the types of wood

There are many types of wood, and each has different properties and requires different handling. Wood is also a natural product that has different properties depending on how the wood grows and lives. Some types of wood have large pores, and others have small, soft pores. To close and fill big pores, you need filler with strong covering power. Some wood has small but deep and tiny pores and will need more fine filler. Make sure you understand the wood and learn how to handle it.