how to tell if wood filler is bad?

When it comes to filling holes or cracks, wood filler is the go-to option. It’s easy to use and readily available at home centers and hardware stores.

But there are a few things you should know about this handy product before using it on your project or repairs. So, let’s discuss what makes wood filler so great—and also some things that could be problematic.

Does wood filler expire?

Wood filler does not expire. However, it does have a shelf life like any other product you would use in your home. The length of time that wood filler lasts depends on several factors:

  • How much moisture is contained in the wood filler? If you place wood filler with a lot of moisture in an environment where it can dry out, then this will cause the wood filler to begin to break down. For example, if you store your can of wood filler outside or near a heater vent during winter months and forget about it until springtime when you remember its existence and go looking for it only to find that there’s nothing left but crumbs and dust—this probably happened because the temperature difference between inside and outside caused excessive drying which accelerated degradation. To prevent this from happening again next year, simply keep your cans indoors during winter months!

How do you revive old wood filler?

If your wood filler is too dry, you can revive it by mixing in some water. You want to add just enough water so that the filler becomes workable again.

To revive a dried piece of wood filler:

  • Place the dried-up piece of wood filler on a plastic plate or something similar for easy cleanup
  • Mix in about 50 percent to 60 percent water with the dried-out wood filler using a putty knife (or any other tool that will easily mix together) until you have reached an acceptable consistency again
  • Apply this new concoction to whatever surfaces where it has been applied before by using either a paintbrush or trowel depending on what kind of surface it was used on originally

What consistency should wood filler be?

  • Thick – Fillers should be thick enough to hold their shape. You can often see this as a layer on top of the wood, especially if applied in two or three coats.
  • Sticky – If your filler is too thin, it will not be able to stay in place on top of the wood and may fall through the cracks when you try to apply it.
  • Easy to apply – A good filler should be easy to spread with a putty knife or similar tool so that you can evenly coat all surfaces.

Does wood filler get as hard as wood?

The answer to this question depends on the type of wood filler. Most types will get harder than wood, but some are more flexible and others are even more brittle. If you’re using polyurethane-based wood filler, you should find that it remains pliable for years. On the other hand, epoxy-based fillers tend to harden more quickly—in just a matter of weeks or months—and can become as brittle as glass if exposed to extreme heat or cold conditions (think summertime in Arizona).

What’s the difference between wood putty and wood filler?

The difference between wood putty and wood filler is simple but important. Wood putty is a wet paste that you apply to the surface of a hole or crack in order to fill it.

When the wood putty dries, it hardens into a solid substance that looks just like the rest of your piece of furniture.

Wood filler, on the other hand, is a dry powder that you can mix with water until it has a thick consistency similar to cream cheese or yogurt.

Once mixed together correctly, you can apply this mixture directly to your project–no need to work with messy liquids!

Once applied and dried out completely (which takes about an hour), your project will appear as if nothing ever happened!

How long should I wait to sand wood filler?

The amount of time needed to wait before sanding depends on the brand and type of filler you use. Some fillers can be sanded within a few hours, while others may need to sit for days or even weeks. To make sure you don’t damage your project, it’s best not to rush this step. If you find yourself wondering how long wood filler should dry before applying another coat or sanding down, here are some general guidelines:

  • If using paper-backed fiberglass cloth and epoxy resin, wait at least 24 hours before sanding; longer is better if possible (up to 1 week).
  • For polyester resin products like Bondo® Easy Sand™ Easy Sand™ Handy Repair Filler Kit, give it 48 hours before starting sanding (this product is made by 3M®, who also makes masking tape).

Can you add water to dried wood filler?

You can add water to dried wood filler if you want to soften it. You can also add water to make it easier to sand, apply, or paint.

Can I mix water with wood filler?

Yes, you can mix water with wood filler. Once you’ve added the water, stir the mixture until it is smooth and uniform. It’s important to note that how much water you need depends on the particular product you’re using.

If there isn’t enough water in your mixture, it will be too thick and not adhere well to the surface of your project; if there is too much water, then it might runny and cause a mess while applying it.

For more information about using wood fillers effectively, check out our guide to using wood fillers for interior projects!


We hope this article has helped you understand the difference between wood filler and putty, and what to do if you have either of them around your house.

If you’re still unsure about whether or not your wood filler is bad, check out our other articles on what to do with expired products and how long they last!

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Martin Flood

Martin Flood has been working in the construction industry for over 20 years as a general contractor with expertise in remodeling projects that are large or small. He has furthered his career by specializing in epoxy resin flooring, providing excellent service to both commercial and residential clients. Martin’s experience enables him to offer professional advice on how to choose the right type of project based on your needs and budget.

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