A
grain filler (also called
pore filler or
paste wood filler) is a
woodworking product used to achieve a smooth-textured
wood finishing by filling pores in the
wood grain. It is used particularly on open-grained woods such as
oak,
mahogany and
walnut, where building up multiple layers of standard finish is ineffective or impractical.
Composition
Grain fillers generally consist of three basic components: a binder, a bulking agent, and a
solvent.
The binder is a wood finish, and in the case of oil-based fillers is typically a blend of oil and
varnish. Water-based fillers use
acrylic resin or
polyurethane. The type of binder determines the solvent: oil-based fillers usually use
mineral spirits, while water-based fillers use water. Both types commonly employ
silica as a bulking agent, as it resists shrinking and swelling caused by changes in
temperature and
humidity.
Other bulking agents may include quartz powder,
wood flour, and talc.
Use
Woodworkers apply grain filler before other finishes on open-grained woods to achieve a "full finish" with a smooth, reflective surface.
Species such as ash,
oak,
mahogany, and
walnut fall into this category, while tight-grained woods such as
maple and
cherry can achieve similar results with just a few coats of finish.
Before application, the surface is sandpaper and wood putty to conceal imperfections, which would otherwise be accentuated by the grain filler. The filler is brushed both with and against the grain and excess is scraped off. After partial drying, the woodworker typically uses a piece of burlap to remove remaining excess.
See also
