Does Wood Filler Dry Hard?

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Even if you are a highly-skilled woodworker, you will have unsightly nail holes, cracks, and joints in your woodworking projects. You would typically reach for some wood putty or wood filler to cover them up. Both products serve similar purposes but they are different in composition. In this post, we look at particular aspects of wood filler.

Does wood filler dry hard? The answer is yes, but it differs depending on the type of wood filler you use. Wood filler consists of pulverized wood waste mixed with a binding compound. On drying, the mixture becomes hard. The hardening of wood filler is convenient as it enables us to smoothen down the surfaces and paint over them.


Young carpenter in work clothes using scraper and wood filler i

Manufacturing wood filler involves using wood byproducts such as sawdust and pulverized wood. We then mix these wood byproducts with water or a petroleum-based substance.

While water-based wood fillers can only be used indoors, petroleum-based wood fillers serve well in outdoor applications as well. Both types of wood filler dry hard. Although wood filler provides a strong bond it will not improve the strength of the wood joint.

Wood filler usually comes without any additional color added to it. Once it hardens, you can sand it down, apply a finish, or paint over it.

Water-based vs Oil-based Wood Fillers

As we mentioned above, you get two types of wood filler – water-based and oil-based or petroleum-based. Water-based wood filler tends to have a crumbly texture. You can use water to clean up after using water-based wood filler.

On the other hand, you cannot use water to clean up petroleum-based wood filler. You will need a chemical solvent. The typical solvents for cleaning up petroleum-based wood filler are acetone and mineral spirits.

When you use oil-based filler on a joint, it not only fills the gaps but bonds the wood parts together. So, when you use oil-based wood filler on joints, they are less likely to come apart later on.

How Does Wood Filler Harden?

Young carpenter in work clothes using wood filler in finishing

Wood filler cannot harden without the aid of a hardener. The process involves a chemical reaction between the hardener and the wood filler. In this reaction, we consider the hardener to be a catalyst. We call the chemical reaction here a “free radical polymerization (FRP).”

Wood filler contains resin which prevents wood filler from hardening unless you add the hardener. If you don’t add hardener, the resin finally runs out and the oxygen in the air will enable the wood filler to dry. But without a hardener, the wood filler can take two to three years to dry completely.

Due to the above reason, it is imperative to use a hardener with wood filler. Usually, the manufacturer provides hardeners separately along with the wood filler.

The hardener also contributes to the prevention of the adverse effects of the environment on the wooden surface that can occur with variations in atmospheric temperature and humidity levels.

How to Make Wood Filler Dry or Harden faster

If you want to make wood filler dry faster, there are many things you can do. You can use these methods on both water-based and oil-based wood fillers. Here are the steps to follow:


Cleaning is one of the most important stages of any woodworking project. The presence of contaminants like dust, debris, and stain residue can hamper the drying of the wood filler.

Remove additional wood splinters and large debris with a scraper. The gap to be filled becomes more visible clearly defining the site of the job. Once you have completed cleaning the job site, place the workpiece in a clean, dry, and warm place.


On opening the wood filler container, you will find a hardener tube within. If you don’t receive a tube of hardener, you must procure it separately. Without a hardener, your wood filler will not harden.

If you buy hardener from the market, ensure that it is compatible with the wood filler. You can get the technical details of your wood filler from the manufacturer’s information on the packaging.

Before you remove the wood filler from the container, read the instructions on the packaging carefully. Pay special attention to the mixing proportion of the hardener to wood filler. If you add too much hardener, you won’t have enough to cover all the filler in the container. If the hardener is insufficient, the filler won’t harden properly.

Next, remove the wood filler from the container with a putty knife and add it to a scrap wooden board. Now, squeeze the required amount of hardener onto the wood filler. Mix both the components thoroughly until they make a homogenous mass.


Once you have thoroughly mixed the wood filler and hardener, using the same putty knife, start applying the wood filler mixture to the job site. Apply the mixture firmly but in thin layers. Thick layers tend to contain moisture extending the drying time.

Try to wait for each successive layer to dry before adding on another one, as if you were applying paint. It creates the best bonding and a solid layer over the gaps you are filling.

Keeping Warm

As we mentioned above, you need to place the workpiece in a warm and dry area. This is to enhance the drying and curing of the wood filler. Once you have completed applying wood filler, you need to wait for at least 20 minutes for it to dry.

Ensure to place your workpiece in a warm area like in a sunny area of your patio or on a sun-filled spot in the yard. If the weather isn’t sunny, you can use a hair drier to keep the area warm.

Keep the workpiece in the warm area until the wood filler no longer feels tacky to the touch.


Womens hands sanding the wood floor before painting.

Once the wood filler has dried and hardened completely, you can file it or sand it down to smoothen the outer surface of the wood filler. Continue to apply sandpaper until the surface is smooth enough for your satisfaction. Once the surface of the wood filler is sufficiently smooth, you can apply a finish or paint over it. This adds the final touch to conceal imperfections in the wood or between joints effectively.

Caution: Ensure to wear a respirator or face mask while sanding. The area should also be well-ventilated and you might do well to wear safety goggles to avoid getting fine dust in your eyes.


Does wood filler dry hard? Yes, it does. But the degree to which it might harden largely depends on how correctly you process it. Wood filler hardens faster and harder than wood putty. It is a versatile substance that can add a smooth finishing touch to all your woodworking projects.

Follow the steps outlined in this post, and you will find that wood filler becomes an indispensable part of your woodworking workshop. Use the information here to get the most from wood filler in your work to make every project a great one!\