Does Wood Filler Need Hardener?

Wood filler can be a lifesaver for even the most experienced woodworkers or carpenters.  It gives you a second chance when you made a mistake or hides some of your more unsightly work. At some point, however, everyone worries about if wood filler will do the trick. And if you work with hardwoods or ancient, delicate wood, you must have wondered if you needed to add hardener to your wood filler.

Wood filler usually contains a hardening compound. However, this differs from the brand, type, and base. Hardeners are usually applied to either a knot that structurally compromises the wood or a damaged part of the wood. It's the last choice amongst many woodworkers to save a broken or rotten piece of wood. 

Wood fillers can be used to reinforce softwoods or rotten woods structurally. However, this is usually only a stopgap without using a hardener as well. You can use both in conjunction to save ancient, fragile woods. For normal use, the wood filler should suffice. Below we will discuss the different types of wood fillers and hardeners commonly used by woodworkers and carpenters.

What is wood filler? 

Wood filler is a substance used by carpenters, DIYers, and woodworkers to repair or hide imperfections in the wood. It is usually composed of sawdust or wooden particulates and an adhesive chemical paste. Wood fillers can have different bases, depending on your needs. Depending on their base, their function and use can change dramatically.

Ensure that you research and study your wood before acquiring or using wood filler. Applying the wrong wood filler can have adverse effects and sometimes damage the wood to which it is applied. Most wood fillers are easy to use but do require a curing time. Be sure to let your wood filler cure for the best results.

Different types of wood filler

Wood filler has been in use since ancient times. Most carpenters learned how to make it from their teachers or instructors. The home-made wood filler consists of cold wood glue and sawdust from whichever wood are currently working on.

Most wood fillers should be used on untreated wood to ensure that it bonds with the wood. If you are unsure which kind of wood filler to use, read on to learn about some of the different types of wood filler and when to use it.

Home-made wood fillers

Home-made wood fillers, as stated above, are almost as old as woodworking itself. Most recipes include white glue, carpenter's glue, resorcinol glue, or epoxy cement. The most commonly used, however, is polyvinyl acetate resin emulsion glue, or white glue. This is because every woodworker has it in his workplace.

Furthermore, it is cheap, easy to come by, dries quickly, and does not stain most woods out there. To make your own, mix the white glue and sawdust until it forms a thick paste. Apply generously to the chosen area and allow it to dry for a day. Be aware that white glue is heat-sensitive, so for best results, seal or treat the wood after applying it.


Latex- and solvent-based fillers are pre-colored wood fillers that come in a variety of wooden tones. They are usually used on treated wood to conceal cosmetic damage.

Their ease of use and pre-mixed availability make them a favorite. They are easily applied with a putty knife and then sanded down. Latex- and solvent-based fillers do not have much structural strength.

The experts recommend using for openings or holes smaller than ½ inch or 2.54cm. They will not hold a nail or screw and will crack or sink if misused.

Epoxy Based

Epoxy-based fillers are fillers that usually contain a potent chemical epoxy. It bonds in or around the crack in the wood and often forms a harder substance than the wood itself.

Use it carefully as it does not sand off easily, and using an excess amount, will call attention to the repair. It can be clear or colored, and you can drive screws into it. It has a plastic appearance and therefore is mostly used when structural integrity is more important than aesthetics—best on both treated and untreated kinds of wood.

Exterior Wood Filler

Exterior wood filler comes in cans and has elastomeric properties. This means that it is perfect for outside use as it shrinks and expands with the weather. It can be applied with a putty knife and painted over if desired. It is often paired with Acrylic latex or butyl caulk to help seal and weatherproof exterior woods. Exterior wood filler should be applied to treated wood for the best results. Elmers and Minwax have a good selection of fillers on Amazon(Check Prices here)

Wood Putty

Wood putty is oil-based and is typically meant for exterior use on wood that has already been treated. Because of the oil base, it resists moisture and will never truly harden. Wood putty will retain some flexibility even after it has been cured and cannot be sanded. Minwax wood putty is an excellent choice.

Wooden Bondo

Wooden Bondo is a relatively new product that most carpenters swear by for quick patch jobs that require both strength and reliability. It is water-based and can be sanded and stained or treated afterward. It is easy to apply and penetrates deep into the wood for maximum strength. The secret behind this wood filler's success is because it is a two in one product, a mix of wood filler and wood hardener, which is why it cures quickly and strengthens the wood so well.  

What is a wood hardener?

Wood hardeners are chemical substances used by woodworkers and carpenters to strengthen the structural integrity of old, fragile, rotten, or even broken wood. They seep into the wood when applied correctly and strengthens the wooden fibers while protecting them against other elements like moisture.

Wood hardeners like wood fillers have a curing time to be effective. Ignoring the curing time will result in splintering or, worse, destruction. Hardeners are generally used before wood fillers to prepare the wood before making repairs. Some manufacturers even boast that the hardened wood is strong enough to carry its own weight after the treatment process.

Different types of wood hardener

Wood hardener can really save your project and even restore antiques to their former glory. However, the price is patience and care, as fragile or old wood normally cannot be rushed for restoration.

Below we will discuss some of the more prominent wood hardeners and conditioners. So if you are in the market for something that will help restore a wooden family heirloom that's fallen on some bad times, read on.

Miniwax 41700000

Miniwax 41700000 high-performance wood hardener is at the top of the list for many woodworkers and carpenters for wood restoration. It has a watery consistency that enables it to penetrate deep into wood and cures into a rock hard base. It protects and seals the wood while drying quickly.

Miniwax 41700000 high-performance wood hardener is best paired with its sister product Minwax High-Performance wood filler for general wood repairs. Be aware that this product is solvent-based, so please follow the user instructions carefully. (Check out the current price on Amazon)

PC Petrifier

PC-Petrifier water-based wood hardener is especially effective when dealing with the damage done by insects. It has a thicker consistency than Miniwax 41700000 high-performance wood hardener and is a little easier to use. PC-Petrifier water-based wood hardener can be sprayed, brushed, or injected into your wood. 

After curing, this product is nontoxic and environmentally friendly, making it great for environmentally conscious users. Because of this product's versatility, the hardened wood can be painted, primed, or filled afterward. Be aware because this product is water-based, only certain fillers will work together with it. (Check this product out on Amazon here)

Bondo Rotted Wood Restorer

Bondo Rotted wood restorer is the wood hardener that is part of Wooden Bondo wood filler. As can be expected, this is an excellent general hardener for rotted wood. It penetrates deeply and stabilizes the soft spongy rotted wood fibers and later sets to a solid base.

This product dries and cures very quickly and is water-resistant, making it ideal for interior and exterior use. For the best results, use this in conjunction with Wooden Bondo wood filler.


Liquid wood kits are top-rated and rated as the best products for restoring and renovating rotting wooden material. The reason behind this is that it is suitable for almost any type of wood and can make even pine as durable as oak.

The kit consists of two tins separately marked Part A and Part B and should always be used together for the best results. It is durable for structural repairs and can be drilled, sawed, glued, painted, carved, and even routed. Liquid wood also acts as a primer, meaning you can paint on top of it after curing. Although marketed for both interior and exterior use, this product is less suited for outdoor exteriors.


Restoring old furniture or doing maintenance on your wooden house does not have to be complicated or frustrating. Any of the products mentioned above can speed up restoration and, in some instances, save you some money. However, if you only need to make cosmetic repairs, you can get away with using wood filler without a wood hardener.

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