How Strong is Wood Filler

How Strong is Wood Filler?

Invisible joints, pocket-hole joinery, and dowels have something in common.  They are all ways of hiding screws and nail holes.  The use of wood filler is another when screws are countersunk or a nail punch is used.  What about larger gaps, though?  How does wood filler compare with wood putty?  Is it durable?

Let’s examine all things wood filler. 

What is Wood Filler?

We were all beginner woodworkers at some point and prone to mistakes.  And sometimes, wood we want to use in our projects has minor imperfections or a blemish we want to hide.  Fortunately, we have choices, including both wood filler and wood putty. 

Wood fillers contain real wood fibers; typically, a wood byproduct like sawdust is suspended in a binder that may be water or petroleum-based and dries to a hard finish.  Although they dry hard, they add no structural strength to the wood it is applied on.

Wood fillers come untinted – no color other than the color of the wood from which the sawdust came. Applied to your unfinished wood, and once thoroughly dried, wood fillers can be sanded smooth to the surface of the material, as well as stained or painted.  The fact they dry hard and are stainable distinguishes them from wood putty. 

Wood fillers are easily applied with a putty knife, pressed into the hole or large gap being filled, and smoothed by drawing the putty knife over the filler, so it is flush with the surface of the wood.

Water-Based vs. Petroleum-Based Wood Filler

Water-Based vs. Petroleum-Based Wood Filler

There are some differences to be considered when choosing between the two:

  • Water-based wood filler tends to be a bit more crumbly, although water can be added to create a smoother consistency, and water can be used to clean up your putty knife after using it with water-based fillers;
  • Water-based wood fillers dry quickly, with some products drying in as little as 10 minutes time;
  • Water-based wood filler’s consistency makes it a bad choice for finished woods but an excellent choice for porous, unfinished woods to which it takes very well.
  • Petroleum-based wood filler, on the other hand, have an inherent smoother consistency and are more effective in protecting wood against humidity and moisture;

How To Make Your Own Wood Filler

We’ve already mentioned that a wood filler’s constituent parts are a wood byproduct like sawdust and a binder.  It’s very likely you already have everything you need in your woodworking shop to make your own, and the process is very easy.

Grab a paper plate, some Elmer’s glue, and some sawdust.  Mix it well, and it’s ready to use.  Bring it to a beyond-crumbly consistency, fill the hole or gap, allow it to dry (the instructions on the container of glue will tell you how much time it needs), sand it flush, and apply your finish.

Is Wood Filler Durable?

Yes, wood filler is durable.  It dries quickly and hard, as we have said.  One brand, Minwax High-Performance Wood Filler, can dry in as little as 10 – 15 minutes and can be sanded in as little as a half-hour after hardening.  Whether it’s a new project or a repair job, it won’t hold up the completion of your project with those times.

Which is Stronger:  Wood Filler or Wood Putty?

As we so often say here at Obsessed Woodworking, the right tool for the right job, or in this case, the right materials for the right job. 

Wood filler dries quickly and very hard, can be sanded, stained, or painted.  However, the fact they dry very hard dictates where it is used, and in the case of wood filler, that “where” is on inside pieces.  Environmental factors that lead to expansion and contraction can affect the wood filler and cause it to crack.  Indoor environments are relatively static with temperature and humidity, and cracking is far less likely.

Wood putty, however, is more flexible and can withstand a greater degree of temperature and humidity fluctuation.  Wood putty is also a better choice for outdoor projects.  Its use on raw wood can be problematic, though, as its chemical composition can damage it.

The question of stronger, then, depends on how and where and on what each is used.  Consider the differences each brings to a project and where the piece you are building will be used to determine which is the better choice.

Is Wood Filler Strong Enough to Screw Into?

Is Wood Filler Strong Enough to Screw Into

It depends on a few things, but it is possible.  There is another type of wood filler beyond water-based and petroleum-based, and that is epoxy wood filler.

It’s used in the form of putty or a pourable liquid.  It will fill holes, gaps, or cracks and even coat wood surfaces to prevent further decay or damage.  In short, it’s an excellent choice for repairing wood that has developed some rot or been damaged.

One such epoxy wood filler is Bondo Home Solutions Wood Filler.  It offers a quick and permanent solution for repairing and strengthening a piece of furniture that has been damaged or is experiencing some decay.  It dries for sanding in about 15 minutes.

Bondo doesn’t shrink and creates a strong and durable bond.  It’s water-resistant and can be used for both interior and exterior projects.  Once it has cured, it acts just like wood and can be painted or take wood stains and make it look just like it had always been a part of the piece you are repairing. 

Now, as to it being strong enough to screw into, the answer is maybe.  It might not be able to support something weighty, but for lighter load-bearing pieces, it will easily hold screws well. 

So, the right product for the right job is once again the rule. 

The Other Wood Filler Type

We have water-based, petroleum-based, and epoxy wood fillers.  However, there is another worth mentioning, and that is plastic wood fillers.  DAP is the best known of the latex-based fillers, and it, too, has its highest best uses.

As it is referred to, plastic wood is a high-quality latex-based wood filler developed to create a surface that looks and acts like real wood.  When it has dried, it can be sanded, cut, planed, drilled into, nailed into, screwed into, painted, and stained just like real wood.

For a small hole or gap to fill, something shallow and needing a low volume of filler, it can dry in as little as 15 minutes; for something larger and deeper, more than a quarter-inch deep, it might be 2 – 24 hours.  However, once dried, it’s good to go with whatever finishing elements you’ve chosen for your project.

Plastic wood filler is both durable and strong, but it is not as strong as an epoxy wood filler.   If maximum strength is a concern, and even though it is the more expensive option, choose an epoxy wood filler.  Either can take a screw easily; the epoxy wood filler’s added strength is the better choice for greater weight support.

Here’s a video that shows the application of a plastic wood filler like DAP.

Can You Use Wood Filler Over Screws?

Yes.  If you plan to paint your project, using wood filler over screws is a good choice.  Use a narrow-width putty knife blade to maximize your control of the tool and spread a small amount of wood filler over the screw and hole. Spread the filler with the blade, so it is flush with the surface of the wood.

Follow the instructions for the brand you are using for drying time to let the filler set.  Then, sand and paint. 

Keep in mind our earlier discussion about cracking caused by environmental factors, and use this approach only for indoor pieces.

We’ve filled you in, so to speak, on the various options for wood fillers and when and how best to use them.  We found one more video that might be helpful for you if your project is trim work around the house.  It’s certainly a place where both screws and nail holes would be unsightly. 

You’ll find a helpful video here.

Give that project a truly finished look by hiding away screws and nail holes.  Pick the right filler for the right job, and take pride in the results of your hard work.