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Applying Wood Filler in Woodworking Projects

Wood filler supplies

Woodworking is an art that can reach unbelievable perfection. But even if you are a man of great experience, cracks and holes are bothersome.

You can deal with these gaps with either putty or wood filler. The two are different, though the terms are often used interchangeably.

As a woodworker, you should know the difference as the results of using each of them vary. Wood putty is flexible. Even after the putty dries, it remains pliable to a certain extent. On the other hand, wood filler hardens after drying.

Wood Filler In Contrast to Wood Putty

Wood Filler

Wood filler consists of bits and pieces of wood in a binding agent. The binder is either water or petroleum formulas. If it’s a water solution, you can use it indoors, whereas a petroleum wood filler is better for outdoor usage.

Wood fillers bond wood parts together. It dries to be hard just like wood, but they are not ideal for holding wood together. That is not the purpose of wood fillers.

As the name suggests, wood fillers simply fill gaps in the wood. Though wood filler is not super glue, it bonds with wood better than putty.

Scraping wood filler onto wood

Wood Putty

Putty is mostly polyurethane or epoxy, both synthetic materials. When you apply putty, it does not harden like wood fillers do. Instead, it turns into something that resembles a kind of rubber.

Wood putty is good for filling cracks and holes. The application is after finishing. Furthermore, putty comes in a wide spectrum of colors so you can pick the one that matches the color of the wood you need it for.

Wood fillers are a bit difficult to apply, but they are more useful during the woodwork process.

Getting The Right Wood Filler

Wood fillers come in water or petroleum mixtures. The water type has a texture that seems somewhat crumbly.

You can figure out which one is a water solution wood filler by reading the instructions. It should say that water is what you clean up with.

Petroleum solution wood fillers, on the other hand, have instructions to clean with a chemical solvent. Examples of such chemicals include acetone or mineral spirits.

Both types of wood fillers are good for filling gaps and bonding wood parts together. After hardening, there is a lower chance of further cracks in the future.

However, wood filler is not a substitute for wood glue or mechanical fasteners. Yes, you will get structural stability to a certain extent, but for the most part, it’s for visual smoothness. For proper reinforcement, you need wood glue or, even better, metal connectors.

Things You Will Need to apply Wood Fillers

First of all, you need to get the right wood filler. If it’s an indoor project then get a water-based solution, and if outdoor then get a petroleum-based solution.

Next, you will need a putty knife to apply the wood filler. Also, you will need rags to keep things clean.

As stated above, if you are using a petroleum solution wood filler, get acetone or mineral spirits to clean up.

After that, get an oscillating sander and sandpaper of different grits to smooth the surface.

Next, get yourself a tack cloth and some wood stain. You can also purchase a shop vacuum, but that is optional.

Applying wood filler

Mixing and Application of Wood Filler

Before applying the wood filler, you need to mix it well. You can do so in the container that it comes in. Mix the wood filler using a putty knife. The objective is to get a smooth mixture that is uniform in both texture and color.

Remember: wood filler gets hard after application. And though you can use sandpaper to make it smooth, the rock-solid filler is hard to smoothen.

As such, don’t just slap on a chunk of wood filler onto the gaps with an excess amount of it bulging out. That will only lead to further obstacles.

Instead, be conservative and delicate when you apply the wood filler. The putty knife may look like a limited tool, but that is not true. The tool gives you the power to apply wood filler very close to complete accuracy. The less you have to smooth out later, the better.

Press In The Wood Filler With Your Putty Knife

Pressing in wood filler

With your putty knife, press in as much filler into the crack as possible. You can then scrape off the extra amount with your putty knife.

When you are dealing with petroleum solutions, act fast as it is quick to dry. Water solution wood fillers, on the other hand, take time to dry, so you have more time to apply the filler and do it perfectly.

Either way, make sure that the filler goes deep into the crack. Also, be careful and refrain from gouging the putty knife into dry areas.

Use Your Finger to Press in the Wood Filler

The putty knife works well to a certain extent, but you also have to use your fingers to push the filler further. Once the filler goes all the way in, scrape off the surface filler.

You should not keep the wood filler on your fingers for too long. Use mineral spirits to wipe your fingers. If the filler is a water solution, then use water to clean your fingers. Keep the blade of the putty knife clean as well. You don’t want the filler on it to harden.

Sanding the Wood Filler

Sanding down wood dried wood filler

After applying the filler, wait for an entire hour before you start sanding.

Some fillers harden rock solid and are hard to sand using sandpaper. In this situation, you will need to use an oscillating sander.

What grit sandpaper for wood filler?

Start with a medium grit, follow up with 180 fine-grit, then finally use a 220 grit sandpaper.

The sanding will leave faint scratches on the filling and the surrounding wood. This is good as it helps the filler take the stain later on.

Wipe The Surface with a Tack Cloth

A tack is a sticky cheesecloth. It is necessary when you are wiping the surface of the hard filler and wood as it removes all the dust before you apply the stain.

If you don’t clear the dust, it will turn lumpy while applying the stain. If the amount of dust exceeds what a tack cloth can handle, use a shop vacuum first.


Staining wood filling

Finally, staining will give the wood and filling protection and similar color. However, the color of the wood and the stain won’t be exactly alike. After all, filling and wood absorb stain differently.

Also, remember that there are different types of stains for water and petroleum solution wood fillings, so make sure you choose the correct one.

Using Wood Fillers Wrapping Up

A wood filling is slightly more difficult to apply compared to putty. However, wood filling is more useful.

Wood putty is flexible even after application whereas wood filling turns rock hard.

A wood filling comes either as a water solution or a petroleum solution. The first dries slowly whereas the latter dries quickly.

Make sure to mix the solution well and fill the gaps with a putty knife and your fingers. Also, keep your knife and fingers clean as filling hardens to avoid any accidents.

Sanding might require an oscillating sander as wood filling sometimes gets too hard for hand sanding. Once sanding is complete, wipe with a tack cloth then apply the stain. The end product is worth the hard work you put in.

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