When I took my first steps into woodworking many years ago, I thought all wood fillers were the same.
Whenever I wanted to fill a nail hole or a crack, I bought the first wood filler I came across, smeared it in the gap, and I was done.
As it turned out, I hadn’t always used the best wood filler for the project I was working on.
Now, so many years later, and after a few experiences, I want to save you from making the same mistakes.
That’s why I wrote this clear article about wood fillers, so even if you’re not a woodworker, this can be understandable.
To better understand wood filler, you can divide them into 2 categories:
First, there are wood fillers. These are the best wood fillers for use on bare wood.
Then you have wood putty. These are the best wood fillers for use on wood that have already been given a finish.
Wood putty itself can be further subdivided into a wood putty malleable version and wood putty wax sticks.
So those are 3 types of wood filler that you will discover all about in this article.
Plus, in this blog post, I’ll give you even more answers to frequently asked questions about wood fillers.
So at the end of this blog, you will know everything about wood fillers, and you will never have to make the mistakes I made myself.
- What is the difference between wood filler and wood putty?
- How big a hole can you fill with wood filler?
- How do you fill a large gap in wood?
- How long does it take for wood filler to harden?
- What wood filler to use?
- What wood filler to use on rotten wood?
- Can I make wood filler from sawdust?
What is the difference between wood filler and wood putty?
Wood filler can be used to fill cracks in bare wood, which is covered with a top coat after filling the cracks.
Wood putty can be used to fill cracks in wood that cannot be covered because they are already covered with a topcoat.
In a short among of time, wood filler will dry out, harden, and can be sanded.
This type of wood filler can be stained or painted.
After applying a top coat or stain, you will no longer see the wood filler.
For example, If you plan to repaint that old cabinet, cracks can be filled with wood filler.
Wood putty is malleable and hardens only to a certain degree.
Wood putty can be used to repair flaws on wood where the finish is already there and cannot be removed for some reason.
Because of this top coat, you can no longer sand the wood putty and the wood putty can not be covered with stain or paint.
However, by using matching colors, or mixing different colors, wood putty becomes almost invisible on the wood.
For example, If you have an old stained chair and one of the legs is broken, you can fix it with wood glue and disguise the crack with wood putty.
How big a hole can you fill with wood filler?
If you want to fill holes or cracks in wood with wood filler, keep in mind that these should never be larger than 10 mm (3/8 inches).
When larger gaps or holes will be filled with wood filler, the expansion or contraction of the wood can cause the wood filler to break.
For wood putty, the holes, or crack, should never be larger than 3 mm (1/8 inches).
If you want to fill large cracks, it is recommended to apply the filler in several layers.
Always prepare the wood well, like sanding and removing loose parts and dust, before applying the filler.
How do you fill a large gap in wood?
If your openings are larger than 10 mm (3/8 inch) you will no longer be able to use wood filler due to the risk of cracking and eventually loosening of the filler.
To fill large holes in wood, you can use caulk to give the wood its original smooth finish.
However, if you have really large holes in wood, it is recommended to glue a new piece of wood into this hole.
To seal the cracks, you can use wood filler.
How long does it take for wood filler to harden?
It takes approximately 2 to 6 hours for the wood filler to fully cure.
Drying time will depend on temperature and humidity.
The colder or more humid it is, the slower the filler will cure.
What will also play a major role in the time to allow the wood filler to harden is the thickness in which this filler has been applied.
Thin layers dry out faster than thick layers.
This is different for wood putty.
In fact, wood putty does not harden completely.
It is a malleable product and loses its flexibility to a certain degree.
How can I speed up wood filler drying?
You can significantly increase the drying time of wood filler by applying several thin layers.
Allow the wood filler to dry between each coat.
This way, the water present can evaporate more quickly from the filler.
With thick layers, the moisture will only evaporate from the top part of the layer, so that only the top layer will become hard.
As a result, the filler that is deeper in the crack will harden much more difficult and slower.
What wood filler to use?
The first step in knowing which wood filler to use, is to look at the wood that needs to be filled.
If the crack is present in bare wood, you need a wood filler.
If the crack is present in wood that has already been given a finish, you must use wood putty.
1. When to use wood filler?
The purpose of a wood filler is to repair minor defects in wood up to 10 mm (3/8 inches).
When defects, such as holes, cracks, or scratches, are present in bare wood, you can use this type of filler.
You apply the product with the improvement of the surface of the wood in mind.
After filling the area, you have to wait until the filler has hardened.
When the filler is dry, you can sand the surface.
After sanding, this type of wood filler can be stained.
2. When NOT to use wood filler?
Wood will expand or contract under the influence of temperature or humidity.
A filler will not have the same flexible properties as the wood.
If the difference in flexibility becomes too great between the wood and the filler, the filler will break.
Knowing this, it is therefore recommended not to use wood filler
- in damp areas,
- near water,
- in areas where environmental factors fluctuate greatly.
3. How to use wood filler?
- Step 1: Sand the surface where you will apply the filler.
- Step 2: Remove All Dirt and Dust.
- Step 3: Apply the filler with a putty knife. Press the filler well and apply a little too much so that it bulges.
- When it dries out, there is a chance that the filler will set in.
- Step 4: Let the filler dry for about 20 minutes.
- Step 5: Sand off excess filler until you have a smooth and flat surface. Use suitable sandpaper for this.
- Step 6: Apply a finish coat of stain or paint.
If you want to know more about how to determine the right sandpaper for your project, be sure to check out my blog: The perfect sandpaper grit guide for woodworking.
Everything you need to know about sandpaper can be found in this article. It will no doubt give you a better understanding of the proper use of sandpaper.
There is also a FREE downloadable guide available to help you determine the right sandpaper grit.
4. What wood filler to use?
Here are a few examples of recommended wood fillers.
5. Epoxy wood filler
Epoxy wood filler is a type of filler that can hold structures.
So if you have an outside corner where a piece is missing, this is the perfect filler for that.
When this hardens, it becomes as hard as wood.
It’s a two-component product where you can take a slice of any section you want, work it all together into one, and then repair the damage on the wood with it.
It will dry in about 30 minutes and cure in 30 minutes.
Once the epoxy wood filler is hard, this type of filler is strong enough to hold a screw.
6. A small recap on wood filler
1. When to use wood putty?
The purpose of a wood putty is to repair minor defects in wood up to 3 mm (1/8 inches).
Wood putty can be used on indoor and outdoor projects.
Wood putty retains its structure very well and is also resistant to water and high temperatures.
When defects, such as holes, cracks, or scratches, are present in wood with a topcoat, you can use this type of filler.
Remember that this type of filler doesn’t completely harden.
So due to that, and to the fact that there is already a nice top coat on your wood, you cannot sand this.
Wood putty is available in different colors.
So you will be able to find a matching color for the project you are working on.
Is there not a color that matches the color of your project?
Then combine different colors of wood putty until you match the color. When you combine colors, do so with products from the same manufacturer.
This way, you are always sure that the ingredients do not react with each other.
2. When NOT to use wood putty?
Never use wood putty on unprocessed wood.
Due to the ingredients used in making wood putty, the surface of the wood can be damaged.
Stains can occur after applying wood putty to unprocessed wood.
3. How to use wood putty?
- Step 1: Clean up the surface where you will apply the filler.
- Step 2: Apply the wood putty with a putty knife.
Press the filler well until you have filled the hole or crack completely.
- Step 3: Wipe off any excess wood putty with a cloth.
4. What wood putty to use?
Here are a few examples of recommended wood fillers.
5. A small recap on wood putty
1. When to use wax sticks?
In addition to wood putty, you also have wax sticks.
They are used for the same purpose as wood putty.
When you need to fill nail holes or scratches in wood with a finish layer, wax sticks are very handy.
You can get these wax sticks in different colors so that you always find a matching color for your project.
You can also combine wax sticks just like wood putty to achieve the best result.
In these wax sticks, you have two different types.
On the one hand, there are the soft wax sticks, on the other hand, the wax sticks that need to be heated to melt the wax also called burn-in sticks.
2. When NOT to use wax sticks?
Just like wood putty, you should not use wax sticks on untreated wood to prevent stains.
3. How to use wax sticks?
Wax sticks are super easy to use.
However, there are a few differences in the steps between the soft wax sticks and the burn-in sticks.
I explain the differences below.
When you want to apply wood putty using a soft wax stick, you can follow these steps:
- Step 1: Clean up the surface where you will apply the filler.
- Step 2: Rub the wax into the void by moving the wax stick back and forth.
- Step 3: The excess wax can be buffed with a cloth until the hole or crack is no longer visible.
When you want to apply wood putty using a wax burn-in stick, you can follow these steps:
- Step 1: Clean the surface where you will apply the filler.
- Step 2: Heat the wax with a soldering iron.
Do this immediately over the hole or crack and allow the melted wax to drip into the crack or hole.
Always apply a little too much wax.
- Step 3: Carefully scrape off any excess wax with a hard plastic object, such as an old bank card.
With this, you not only make the surface flat, but you also polish the surface so that the hole or crack becomes invisible.
4. What wax sticks to use?
Here are a few examples of recommended wax sticks.
The wax sticks on the left are soft wax sticks, the ones on the right are the burn-in wax sticks.
5. A small recap on wax sticks?
What wood filler to use on rotten wood?
If you want to restore rotting wood, you need 2 different products than the ones described above.
First, you need to apply a wood restorer that penetrates deep into the soft rotting wood and makes it hard again.
Then you can apply a 2-component wood filler, which consists of a filler and a hardener.
So never use a regular filler on rotting wood.
Always be sure to use fillers that neutralize the rotting process first.
The products used to repair rotten wood are mostly excellent exterior wood fillers.
In a few short steps, I explain how to use a filler on rotting wood.
- Step 1: Remove all soft rotting pieces of wood.
You can use a chisel to do this.
- Step 2: Sand with coarse sandpaper such as P80.
- Step 3: Remove all dirt, paint, and sanding dust.
- Step 4: Apply the wood restorer.
Do this in 4 to 6 layers, leaving a drying time of 2 minutes between each layer.
That is the time it takes for the product to penetrate the soft wood.
After the last coat, wait 2 hours before proceeding to step 5.
- Step 5: Lightly sand the wood with P80 sandpaper and remove all sanding dust.
- Step 6: Mix the filler with the hardener until you get a homogeneous mass.
- Step 7: Now you have about 5 minutes to apply the filler and restore the wood.
After 5 minutes, the wood filler will be hard and unusable.
- Step 8: After 10 minutes of drying, you can sand and paint or stain the filler.
What products to use to repair rotten wood?
To repair rotten wood, you need to look out for an exterior wood filler.
Below I will show you the two products you need to repair rotten wood, or that you can use as an exterior wood filler.
On the left, you see the product that penetrates the rotten wood to make it harder.
On the right, you have the two-component exterior wood filler.
Always make sure you use both of them to gain the best results.
Can I make wood filler from sawdust?
Yes, you can use sawdust to make your own wood filler.
Using your homemade filler can be one of the best matches for the wood that you can achieve. However, keep in mind that using DIY filler can present some problems. You can read all about these issues in my article, 5 Common DIY Wood Filler Problems When Using It.
This is how to make wood filler from sawdust:
By mixing the finest dust, from the wood you are working on, with a binding agent, you can make your own wood filler.
The best binder you can use for this is wood glue, but epoxy can also be used for this.
Don’t you have the matching sawdust available to make your own wood filler?
Then take a piece of wood and sand it with the sander or by hand.
The resulting dust is most ideal for your DIY wood filler.
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Woodworking | DIY | Home decoration