Even though wood is sturdy, certain factors like moisture and cracks have the capacity to weaken it and make it vulnerable. Thankfully, there are ways in which wood can be saved--owing to the advancement in science, there are ways to fill up cracks, protect it from moisture, and smooth out the unevenness of the surface.
Wood sealers, varnish, or different types of stains that have been treated with chemicals are some such examples. Another similar product is a stainable wood filler.
Wood fillers are used to fill open cells or small crevices in open-grain woods and bring about a leveling. Some of the woods that these are used on are oak, ash, chestnut, elm, mahogany, and walnut. Wood fillers (stainable or otherwise) do not let the varnish finish sink into the crevices, and thus prevent the wood from getting a pitted or rippled effect.
Moreover, a stainable wood filler (which is pre-mixed and colored wood) is composed of real wood fibers for good quality sanding. It is also used in high speed sanders. In addition to that, these can be easily cleaned by water, and they are a great option for both, exterior, as well as interior use.
Paste and Liquid Fillers
While paste wood stainable fillers are semi transparent and are used with open-grain wood, liquid fillers are transparent and are used with close-grain wood. A binder, a bulking agent, and a solvent is what makes a grain wood filler. These are better used for horizontal surfaces.
Commercial and Non-commercial
This type is just a categorization of stainable fillers. Non-commercial fillers are those fillers which are mixed by carpenters traditionally. These can be made by mixing fine sawdust into a paste with carpenter's white or yellow glue, shellac, or hide glue. After the filler dries, sand and seal the same using a coat of shellac or hide glue.
There is a wide range of options when it comes to commercial fillers. There are gypsum based fillers, vinyl based fillers, cellulose based fillers and epoxies. Most of these products are calcium carbonate (chalk), mixed with a polyvinylacetate dispersion or emulsion as the vehicle or binder.
The gypsum filler consists of mineral powders that have been mixed with water for forming a crystalline filler which does not shrink or pull away from the edges of the filled area. The epoxies are made up of two-part, petroleum-based resin products. The cellulose based wood fillers are simply combinations of wood fiber and the available binder.
In addition to all these, another type of stainable filler is a cosmetic filler. The paste wood filler comes in this category. As far as paste wood fillers are concerned, sometimes a color that is different from the wood is used to make the grain stand out.
Oil-based crayons, colored fillers, and non-hardening fillers are great for nail holes and tiny dings. These stainable woodfillers do not shrink and come out in a wood-colored rainbow.
At the end of the day, the kind of filler you use will depend on the type of wood you are looking to work on. Generally, the product label will help you decide if that wood filler is suitable for your use.