There are times when the wood you are using in a project will have a hole, a dent, a scratch, or a gap that will need to be addressed. By address, we mean filled with something and then made flush with the surface of the wood.
What you fill them with depends on several factors: indoors or outdoors? Raw or finished wood? Stain or paint finish?
Choices are available for each of those possibilities, and today we’ll discuss the types of wood fillers available for those choices.
Types of Wood Fillers
Wood fillers contain real wood, usually in the form of sawdust. The sawdust is suspended in a medium that binds it, either water-based or petroleum-based, and it dries to a hard finish. Its purpose is to fill the hole or gap only, and it adds no structural strength to the wood.
Wood fillers have no color or tint to them other than any color that may come from the sawdust used to make them. Once fully dried, wood fillers can be sanded smooth and flush with the surrounding surface, as well as stained or painted.
We use a putty knife to apply wood fillers into the hole or gap they are filling, pressing the filler into the hole and then using the blade of the knife to smooth it flush with the surrounding surface. The process is easy and quick, and then the filler is allowed to sit while it dries to a hard finish.
Water-Based Wood Fillers
- Water-based wood fillers tend to be a bit crumbly, but water can be added to create a more smooth and creamy finish to make it easier to work with on filling holes. Water can also be used to clean your putty knife or your fingers, depending on which you used to press the filler in. A damp cloth can also wipe away excess wood filler around the hole.
- Water-based wood fillers also dry very quickly, with some commercial products needing only 10 – 15 minutes before hardening and ready to be sanded.
- Water-based wood filler consistency might make it a bad choice to use on finished woods, but an excellent choice on raw woods that will be more porous and to which the wood filler will take well.
Petroleum-Based Wood Fillers
- Petroleum-based wood fillers are inherently more smooth and creamy in consistency and do not need to be modified before application.
- Petroleum-based wood fillers are more effective in protecting the wood against environmental changes (humidity and moisture) because of the petroleum medium.
DIY Wood Fillers
You can make your own wood filler, too, and it’s pretty simple to do using what you probably already have in your shop.
On a paper plate, mix sawdust from the wood you are working with on your project and some Elmer’s Glue. Go a little beyond a crumbly consistency, fill the hole either with your putty knife or your finger, let it dry fully, sand it flush and smooth, and apply your stain or paint.
Is Wood Filler Durable?
Yes, very. It dries hard, and a wood filler product like Minwax High Performance Wood Filler will dry in as little as 10 – 15 minutes. A half-hour later, it’s ready to be sanded and finished, whether stained or painted.
It’s an indoor remedy for filling holes and gaps, though, especially a water-based wood filler that will be susceptible to environmental changes. It might be nail holes in new trim, or recessed screws, or a piece of furniture, any of which you’d want to have a professional finish that shows only a smooth finish.
Can Wood Filler Take Screws?
Sort of, yes. But don’t try screwing into the types of fillers we’ve discussed above or even your DIY wood filler.
However, you can use another type of wood filler, one that is epoxy-based. It comes in the form of a putty or a pourable liquid. It will do a good job of filling holes and gaps in wood, and even as an overall coating on wood to prevent further damage or decay.
It’s a good choice for repairing damaged wood or wood that is showing some signs of decay. We wrote about this in a past article on repairing a split wood post.
Bondo Home Solutions Wood Filler is one such product. It’s an easy to use product, dries quickly, sandable in about 15 minutes, and will repair and strengthen a piece of furniture that has been damaged or is showing signs of decay.
You can use screws in plastic wood, but with limited application. We would limit the weight-bearing load substantially to something very light, and under those circumstances, it is possible to screw into it.
It doesn’t shrink and forms a very durable bond with the wood. It can be used on both interior and exterior projects. Once cured, it can also be sanded, painted, or stained and help make that damaged piece of furniture look new again.
Finishing a Wood Filler
A fine grit sandpaper will give you the smooth finish, and either paint or stain will be uniform in application over it. Each type is a stainable wood filler, also.
Because wood fillers have real wood as part of their makeup, they stain well as a finish.
All unfinished wood should be primed before being painted. Wood is porous, has a grainy surface, and will suck up whatever is applied to it. A primer has a high solids constitution and will help fill grains in the wood and ready it to receive a smooth coat of paint over it.
The same is true for wood fillers. You should prime it along with the wood, and from a practical standpoint, it’s pretty inevitable anyway since you are priming the wood.
A prime coat will help the finish coats of paint adhere well to the wood and the wood filler and give the workpiece a smooth finish. If you have done a good job sanding the wood filler flush with the wood surface around it, the paint will hide the filler and give a professional look to the finished project.
Wood Putty
Another product to use when filling holes or gaps in wood is wood putty. But, it is very different from wood filler. Wood putty is composed of plastic-based, and petroleum-based compounds, often referred to as “plastic wood,” that will also fill holes in wood.
Unlike wood fillers, though, wood putty does not harden as wood filler does. It isn’t sandable, either. It simply fills the hole. It also should not be used on raw wood, as the chemicals used in its preparation can damage the wood.
Wood putty is meant to be used on finished wood. In fact, wood putty comes in a variety of colors and tints to match the finish of the wood it is being used to fill holes in. It’s pretty neat to be able to use a putty that already matches the color of the stain on the wood you are working on within your project.
Because wood putty does not harden, it is a suitable solution to fill holes and cracks in wood that is subject to expansion and contraction due to environmental changes. This makes it the better choice for exterior use.
As wood expands and contracts with the weather, the wood putty will also change shape and adjust to the changing wood. Wood putty can take anywhere from 2 – 8 hours to dry, but it never hardens.
DAP Plastic Wood is an example of a wood putty, a heavy-duty product. It looks and acts like real wood and can be sanded, stained, or painted just like real wood. It does not need to be primed, however. You’ll want to use an oil-based paint to cover this plastic wood. Again, though, remember this is an exterior solution, not interior projects.
It’s not as strong a wood filler as an epoxy product, but it will do the job. For the strongest wood filler, though, if strength is needed, go with an epoxy project.
The video today is directly on point as to the differences in wood fillers and where and how to use each of the two main types – filler and putty.
In short, if it’s raw, unfinished wood, use a wood filler; if it’s finished wood, use putty. Don’t paint wood putty, as it does not harden, and the paint will simply chip off. Prime wood filler first before painting for the same reason you prime raw wood before painting.
Follow these simple rules, and your project will turn out well and with a professional appearance.