Body Materials in Fillers

Furniture finishers usually prefer paste fillers. Liquid fillers act as sizing, and stop the suction of the cavities of the wood cells, or greatly reduce it, at least. However, when used on ring-porous woods, like oak, ash, or chestnut, such mixtures are too thin to fill completely the large open tracheal vessels located in the spring wood of each annual layer of growth.

Some method of filling these open pores and leveling the surface must be used if you want to achieve a good finish. You can apply many coats of liquid surfacer with quite satisfactory results, provided all the high spots are cut down with fine sandpaper between applications of the finish. The open pores or cell cavities gradually fill up, even with an absolutely transparent or liquid filler. Such a procedure, which was the old-time method of finishing wood frames, wood corner blocks and bar rail moulding, is slow and expensive.

About 50 years ago paste fillers, some of them having a vegetable body, were in common use for finishing all porous woods. It had been discovered that it was better to fill the open cell cavities on the surface of woods having large tracheal vessels with a solid mass rather than with several coats of liquid surfacers.

Various materials from the vegetable world, such as cornstarch and wheat flour, were tried, as well as other supposedly more permanent materials, such as whiting (calcium carbonate), China Clay, or Kaolin (which is a hydrated aluminum silicat) Silver White, (which is a name given to several white silicate earths), plaster of Paris (sulphate of lime), and probably other similar substances were also used occasionally.

All of these materials proved to be more or less unsatisfactory, because they were:

subject to decay or disintegration
not transparent enough
expanded or contracted in the pores
did not harden properly with the binders
were too absorbent of shellac or varnish
failed to meet expectations for some mechanical or chemical reason

Silex, a comparatively new material to be used for the body of wood fillers, appeared in the \"Wheeler\" filler about 1876 and because of its many superior qualities, it has nearly supplanted all other substances, especially in high-grade paste fillers. It is one of the forms of silica made by crushing to various degrees of fineness a dull- colored quartz rock called flint.

Silica, which is very similar to silex, comes from ordinary quartz instead of flint.The particles of silex which are made by crushing rock, are in numerous rough shapes, such as wedges and needles, rather than in spherical forms. Such minute fragments will pack together with a proper binder and make a mass that will not easily break up or pulverize and come out of the cell cavities.

Another good feature of silex is that when mixed with oils it becomes almost perfectly transparent and, unless it is packed in considerable masses or is colored with pigments, it does not obscure the grain to an appreciable extent. The resultant clearness or transparency of the finish depends to some extent upon the fineness to which the silex is ground, because its oil absorption also varies with the size of the particles. Silex, when unmixed with oil, is a white ground powder that is far from transparent.

Silex, a comparatively new material to be used for the body of wood fillers, appeared in the \"Wheeler\" filler in 1876 and because of its many superior qualities, it has nearly supplanted all other substances, especially in high-grade paste fillers.