The very highest grade of floor crack filler, that is practically colorless, but may be colored to match the finish that is to be applied, is made by grinding a good grade of perfectly dry cornstarch in a mixing varnish of the following composition: 165 lbs. hardened rosin are melted in a copper kettle, and when done, 30 gallons strong boiled linseed oil introduced and kept at a simmernig heat until 30 lbs. beeswax (pure country yellow) is also dissolved, when kettle is removed from fire to the thinning room, where 45 gallons spirits of turpentine, that is added, will yield 95 gallons of a vehicle, that cannot be excelled by any other for producing an unshrinkable crack filler, when mixed with enough cornstarch to make a paste of the consistency of soft putty. A trifle of raw Italian sienna will give it the color of light oak on drying. In making the varnish, hardened rosin may be replaced by melting 150 lbs. F. rosin and introducing 15 lbs. air slaked builder's lime, treating it until well fused, before the oil and wax are added.
When dark color is not objectionable and rapid setting and hardening is desired, the cornstarch may be ground in a shellac japan of the following composition: - 40 gallons vanish makers' raw linseed oil and 30 pounds orange shellac V. S. D. are combined in the usual way, in a kettle of suitable size, and fused with 100 pounds varnish makers' red lead, 10 pounds litharge and 15 pounds precipitated black oxide of manganese and held over the fire, until the usual test for japan is had; when the batch has cooled sufficiently, 70 gallons of spirits of turpentine added in the thinning room and the result will be 110 gallons of grinders' shellac japan. When, for any reason, the cost of this is too high, use equal parts turpentine and heavy petroleum naphtha for thinning.
There are other crack and crevice fillers, but these are home made and do not interest the paint maker, because they have to be used immediately after preparation.