do you need to seal wood filler?

Wood filler can be used to repair a wide variety of problems in your home, from small cracks to large holes.

However, it’s important to know that wood filler needs to be sealed before it’s painted or stained so that moisture doesn’t get trapped inside the wood.

This article will explain how to properly seal wood filler using a topcoat and other methods.

Do I need to seal wood filler?

A lot of people wonder if it’s necessary to seal wood filler. The answer is yes! Wood filler will not seal itself, and any untreated filler will eventually crack and peel from the wood surface.

To keep your project looking great for years to come, you need to apply a sealer to protect it.

You can use a variety of different types of sealers depending on the final appearance you want:

  • Varnish, paint, or shellac will provide a soft sheen finish that will hide any imperfections on the surface of your project. This kind of finish works best on smooth surfaces like oak or pine boards because it won’t show off any grain details as well as oil or wax would. If you’re working with plywood or MDF (medium density fiberboard) then these types are also good choices because they won’t interact with acidic glues used in manufacturing these materials (such as urethane adhesives).
  • Oil-based products like linseed oil tend to work well on most woods but may yellow over time due to oxidation; however, this can be prevented by mixing them with an acrylic medium such as Liquin before applying them directly onto wet filler.”

How do you protect wood filler?

  • Sealer: If you want to seal your fillers, you can use a sealer. It’s important that the sealer is compatible with the type of wood filler you’re using. For example, most exterior wood fillings are made from alkyd resins and don’t require a special finish for protection, but there are some water-based fillers that require a different kind of protective layer. Before buying or using any type of wood filler, check the packaging to see whether it needs sealing before painting or staining over it.
  • Paint: Paint has become one of the most popular ways to protect wooden surfaces because it doesn’t require any additional preparation steps before application like stain does (see below). Just make sure that whatever paint you choose is compatible with your existing finishes so they don’t discolor each other when combined!
  • Stain: With stains like Minwax Polyshades® Water Based Wood Dye®, you’ll get everything from rich reds and browns all the way through neutral palettes such as tan & gray tones in between depending on what shade suits your style best.

Is wood filler waterproof?

No. Waterproofing is not needed for most applications, as the water-resistant properties of wood filler mean that it will withstand rain, snow, and other common weather conditions without being washed away.

However, the surface treated with wood filler can be damaged if exposed to long periods of moisture or harsh conditions (like wind and sun).

In these cases, you may want to apply a coat of polyurethane or varnish over the top so that the treated area can weather the elements better.

As noted above though, this isn’t necessary for most people – if you live in an area where there isn’t much rain or snow then you probably don’t need to worry about waterproofing at all!

Is DAP wood filler waterproof?

Yes, DAP wood filler is waterproof. However, it is important to make sure that the wood filler you buy is waterproof. Otherwise, if your walls are not properly sealed, they could get waterlogged.

If you are using DAP wood filler and have already applied it to your wall, there’s no need for further sealing since this product already has its own waterproofing agent in its ingredients.

What happens if you use wood filler without a hardener?

  • You can’t sand it. Since you didn’t use a hardener, your wood filler will not be able to be sanded. The good news is that this means it won’t stick in your hardware and paint, but it also means that you will have some rough edges on the wood where you used the wood filler.
  • It may stay sticky or soft forever, even after drying. This can happen if humidity levels are too high for the wood filler to dry properly (about 50% relative humidity). You’d need to wait for better weather before finishing up work on your project!

Does wood filler harden like wood?

The answer is an emphatic yes. Wood filler hardens like wood because it’s made from wood. But is it really?

The answer to that question is also yes. And no.

Wood filler is harder than the wood it’s filling, which means it’ll last longer and stay stronger when you’re using it in a project.

However, if you don’t let your wood filler dry long enough before painting or staining over it (which can take anywhere from 24 hours to 3 weeks depending on the type of sealer used), then that hardened outer shell can get brittle and crack before the inside has had a chance to fully cure—and cracks are never good news when they come in contact with water or moisture!

How long does wood filler take to harden?

How long it takes your wood filler to harden depends on the type of wood filler. Most wood fillers will take 24 hours to harden, but some may take as long as 72 hours to dry.

Water-based wood fillers can take longer than their oil-based counterparts because water evaporates more slowly, and therefore cannot absorb into the grain of the wood as easily.

Why does my wood filler keep cracking?

First, let’s talk about why some wood fillers will crack. There are lots of reasons why your wood filler may crack or not cure properly.

  • The type of wood filler you are using: Some brands and types of wood filler are more prone to cracking than others. Low-quality fillers tend to shrink as they cure, which can cause them to pull away from the surface they were applied on and create gaps between the cured filler and the surface it was applied on. High-quality fillers tend to be less prone to cracking because they don’t shrink as much when curing.
  • Temperature changes: Wood fillers need certain conditions for proper curing; if any one of those conditions isn’t met (too warm or too cold), then there’s a chance your wood filler could end up cracking when it cures down into its new position after being filled in with putty


As we’ve seen, wood fillers are a great way to fill the gaps in your work. They’re easy to use and come in an array of colors that can match the rest of your project.

But do they need to be sealed? The answer is simple: no! If you’re worried that moisture might seep into your wood filler and cause problems later on down the road then don’t seal it – just let it dry out naturally before applying another coat or two on top.

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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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