Does Wood Filler Harden? (According To Experts!)

does wood filler harden

Wood filler is used to repair scratches, gouges, chips, and wood surface unbalances. Even though the hole is large or small wood filler is applicable.  Wood filler helps to maintain the integrity of the wood.

When I’m repairing my damaged furniture and woodworks using wood filler, I was always wondered, Does wood filler harden?

Here’s what I discovered:

Yes, wood filler hardens. Wood filler does not contract or expand according to the outdoor elements and hardens much faster than wood putty. Because of the hardening behavior of wood filler, it is great to cover major damages on indoor wooden furniture and repair them from inside.

But there’s a lot more to know about the hardening of wood filler.

So, in this article, I’ll deeply discuss how does wood filler harden, does wood filler harden without filler, how long does it take to harden, and how to make wood filler dry faster.

Furthermore, I’ll answer some of the frequently asked questions about the hardening of wood filler.

So, just keep reading!

Does Wood Filler Harden Without Hardener?

No, the wood filler does not harden without adding a hardener. The hardening process happens due to a chemical reaction between the wood filler and the hardener which is also known as the catalyst.

The hardener/catalyst mediates the chemical reaction to harden the wood filler quickly.

Wood filler does not harden in a realistic timescale without reacting with the hardener.

Wood filler and hardener go through a free radical polymerization process with peroxide.

The resin which is included in wood filler prevents the hardening by itself without hardener. Once the resin will eventually run out and atmospheric oxygen will participate to harden the wood filler even without the hardener.

But this process will take 2-3 years to complete. Because resin does not run out that quickly without having a hardener.

Even after it runs out wood filler won’t dry, it only sets.

This is why hardener is an essential compound for the hardening process of wood filler. Without the hardener, there is no use of wood filler.

Wood hardener helps wood filler to strengthen the integrity of damaged wood by protecting the wooden surface from environmental elements like temperature levels, moisture, and humidity.

Wood Hardeners That Help Wood Filler to Harden Quickly

Hereby I have listed some of the best wood hardeners which bond perfectly with wood filler to repair the wood effectively.

Wood HardenerQualities
Minwax high-performance wood hardenerWork well with wood filler dries and harden quicklyHigh penetration ability
Bondo rotted wood restorerWater-resistant high penetration abilityMix well with wood filler

Also, some great wood hardeners are not compatible with most of the wood fillers. Such as,

  • J-B weld original liquid hardener
  • PC petrifier wood hardener

Most of the time, wood filler comes with a tube of wood hardener. So, always make sure to read the instructions and mix them well according to the ratio given to initiate the chemical reaction and make the hardening happen.

How Long Does Wood Filler Take To Harden?

Usually, wood filler completely hardens within 30 to 60 minutes.

But this hardening/drying time can differ from wood filler brand, base, and type. Also, it depends on how many wood fillers have you used to cover up the damaged area of the wood.

If the area is large and deep, you’ll have to use a lot more wood filler amount than usually do.

The drying time will also increase according to the amount of wood filler you use to cover up.

For example, sometimes the drying time can take more than 8 hours on a deep and large area.

If you live in an area with cold damp conditions, this drying time can probably increase more (around 24 hours).

Here’re the drying times of some of the major wood filler products.

Wood Filler ProductDrying Time
Minwax high-performance wood filler2-6 hours
Elmer’s wood filler2- 8 hours
Bondo wood filler30- 60 minutes
Aqua coat wood filler45-60 minutes

However, wood filler dries faster than wood putty.

Does wood putty harden is an informative article to know everything you need to know about wood putty.

The best way to estimate the drying time is by checking the package of wood filler for specific drying/hardening times.

How Long Does Wood Filler Take to Dry Before Sanding and Painting?

Usually, wood filler dries within 2 hours before sanding and painting. But this time can differ according to the manufacturer.

For deep and larger holes, the drying time can be around 2 to 6 hours.

Once you’re satisfied with the result, go for the sanding process with medium to high grain sandpaper.

But before that, you need to make sure that the wood filler is completely dry.

Even though the wood filler completely dries within a few hours. I recommend you leave it for 24 hours to dry before sanding.  Because drying time widely changes according to temperature and humidity levels of the environment.

How To Make Wood Filler Dry/Harden Faster?

There are several ways you can follow to make wood filler dry faster. Those drying methods are applicable for both water-based and oil-based wood fillers in the same way.

Here are the steps you should follow to make wood filler dry faster.

  1. Clean dirt and stain and prepare the hole
  2. Mixing wood filler and hardener
  3. Apply wood filler
  4. Layering the filler
  5. Keep the area warm
  6. Sanding

So, let’s discuss each of the above steps to make wood filler dry and harden faster.

1. Clean the Area

This is the most essential part of any woodworking project. Dust, debris, and stain residue will slow down the drying time of the wood filler.

Take a scrapper and remove any remaining wood splinters and paint chips. Also, scrape off the large splinters as well.

By cleaning the cavity/hole which is damaged, we can give a clear open space for the wood filler to speed up its process.

After cleaning and scraping the whole area and preparing the hole, keep the wood in a warm, dry place to dry faster before going for the next step.

2. Mixing Wood Filler and Hardener

Once you open the wood filler, most of the time there is a hardener tube inside it.

If it doesn’t have you have to get a wood hardener from the market. Because wood filler does not harden without hardener.

But always make sure to check the compatibility of the hardener you buy, with the wood filler that you’re going to use for the task. Otherwise, it’ll be a waste of time and money.

Take a small piece of wood and a putty knife. Take a weight from wood filler you can work with using a putty knife and place the wood filler weight on wood piece board.

This will probably take around 3-4 minutes.

After you are placing the wood putty on top of the board, take the wood hardener tube, and put a bead across the width of the wood filler.

If you haven’t taken enough hardener amount the mixture won’t cure properly, and it’ll stay soft and squishy.

Now take the putty knife and mix wood filler and hardener by scraping and kneading back and forth until you don’t see any more of the weight of the wood hardener.

When you think, you have done enough mixing, do it a couple more times just to be safe.

3. Applying and Layering the Wood Filler

After you do the mixing properly, grab some amount of weight from the mixed wood filler and apply it to the damaged cleaned area of the wood.

Make sure to take thin layers of wood filler to make it dry faster.

Thick layers of wood fillers contain a higher amount of moisture and it’ll slow down the drying process.

So, always go for 1/8-inch thick, thin layers. Thin layers give enough space for moisture to escape through evaporation.

But make sure not to take overly thin layers. They don’t fulfill the purpose of applying the wood filler to the wood. follow your instincts and grab the amount you feel “ok”.

Then apply the thin layers of wood filler layer by layer. I recommend you wait till the applied layer hardens completely before applying the next layer on top of that exciting layer.

By following this method, you’ll be easily making the wood filler dry faster. But this can be troublesome for larger areas because practically it is much difficult to wait till the exciting layer is dried completely.

The main purpose of this process is to do the filling process efficiently without wasting time and excess wood fillers.

4. Keep the Area Warm

After you apply the wood filler, keep the wood warm and dry to complete the drying process. This will probably take around 15-20 minutes. if you keep the wood in a warm area, the generated heat will speed up the drying time.

I recommend you place the wood in sunlight to make to wood filler dry faster. If you live in a place where that doesn’t get much sunlight, you can also use a hairdryer to make the wood filler dry faster.

It will remove moisture that is trapped inside the filler.

Once it is completely dried, you shouldn’t feel tacky or sticky anymore and should feel relatively hard if you start to scratch on it.

5. Sanding

Once the wood is completely dried, take some sandpaper and go over everything. This will give the smooth finished look we wish.

Sanding will also help the filler to dry faster.

Make sure to wear a dust mask while sanding because wood dust is not good for breath. Also, make sure to do this whole process in a well-ventilated area.

After you do the sanding, keep the wood under sunlight or apply a hairdryer to fasten the drying process.

Once you have finished the job, you can apply any color of paint to match it with the rest of the woodwork.

So, that’s how you can make the wood filler hardens faster. Now let’s answer some frequently asked questions about the hardening of wood filler.

Why Is My Wood Filler Cracking?

Wood filler cracks because it hasn’t dried/hardened enough.

The rule of thumb of applying wood filler is to wait for the surface to completely dry before heading into the next step.

Also, the wood filler can crack due to insufficient layers applied. You need to make sure to apply multiple layers of thin wood fillers to avoid cracking.

How Do You Fix Cracked Wood Filler?

You can fix the cracked wood filler by following two methods. One is by scraping the exiting wood filler layers completely and starting over from the beginning.

Wipe it off and start with the right amount of hardener and wood filler as per the instruction manual.

Make sure to wait till the wood fillers dry before heading into each step.

The second method is to coat the cracked wood filler with spar varnish to hide the cracks.

Hopefully, this will hold it in place. This method is good if you’re running out of time.

As a woodworker, I recommend you follow the start from the beginning method because that’s the way to do quality work.

Did I cover all you wanted to know about: Does Wood Filler Harden?

From this article we have widely discussed does wood filler harden and how does it happen and does wood filler harden without hardener.

Furthermore, we have talked about how long it takes wood filler to harden completely and how can we make the wood filler dry faster.

Always, make sure to apply thin layers of wood fillers and dry the surface completely after each process to make things happen faster without wasting any filler.

Also, you can use caulk instead of wood filler.

By reading the frequently asked questions about the hardening of wood filler. you can avoid any mistakes and trouble that can happen in future woodworking projects.

Hope you have gained good knowledge about how does wood filler harden.

So, let’s grab a damaged wood piece with cavities and apply wood filler by following the above guidelines. Have fun!

Walter Parker is a woodworking enthusiast. He is passionate about woodworking projects & plays with woodworking tools having spent over 2 decades as a leader for Woodworking Planet. He wants to make people love woodworking! Read More About Him!

Leave a Comment