With natural wood floors, holes are inevitable. Knots, cracks, spaces between the boards and nails all make holes in the floor. There are several types of fillers to use with different types of holes in a wood floor. Each type of wood filler has its own disadvantages and advantages and works best for a specific kind of project or hole.
Latex wood filler is one of the most commonly used fillers for filling holes in wood floors. It works for filling wood cracks, knots and nail holes. Many latex fillers come pre-dyed to match the colour of stained woods. Simply apply the filler to a hole in the wood, allow to dry, then sand down to the level of the rest of the wood. The problem with this filler type is that it cannot be applied to prefinished wood, and if the hole is large, it is easy to tell where the filler was applied.
Epoxy filler is often used to fill wood holes because it dries in less than 10 minutes in many cases. The filler is mixed with black or brown pigments before it is applied to the hole in the wood. Typically, epoxy filler is only used for knot holes, because it will remain a different colour than the rest of the floor. Knotholes stand out from the rest of the floor anyway, so the colour contrast is not a problem. The problem with epoxy is that it can drain out from the hole before it is dry, and it is difficult to sand down to the correct level due to the extreme hardness.
Prefinished filler is one kind of hole filler that will work with flooring that already has a finish, such as a polyurethane sealer on the top of the wood. This kind of filler comes in several colours, but it is necessary to mix two or three colours to match the appearance of the stained and sealed wood. The filler is waterproof and will not shrink once dry. The problem with this filler is that it dries quickly in the container and can freeze, making it unusable.
Wood putty is another popular choice for filling in holes in wood floors. This putty can be used on finished on non-finished floors. It can be mixed with dyes and other putty colours to match wood grain. It is typically used to fill small holes and cracks, such as nail holes, because of the slow drying time. It can take several days for wood putty to fully cure, which is the main problem with the putty. You can apply this filler without coating over it, or use polyurethane over it for an additional sealant layer.