Talc (hydrated magnesium silicate)
A soft, platy mineral filler that improves barrier properties, sanding and sag resistance in primers and fillers.
Talc is a hydrated magnesium silicate, Mg₃Si₄O₁₀(OH)₂. It is the softest common mineral (Mohs hardness 1), and its sheet-like crystal structure gives it a platy particle shape.
Talc is used as an extender in primers, surfacers and fillers, anticorrosive and barrier coatings, and some floor and architectural coatings. It improves sanding, controls sag and gloss, and can reduce cost.
Its plates align parallel to the substrate as the film forms, overlapping like shingles and lengthening the path water and ions must take to reach the substrate. Talc is hydrophobic and relatively inert, and its oil absorption affects a formula’s critical pigment volume concentration.
Control dust when handling. Use cosmetic or industrial grades from suppliers that certify freedom from asbestos, and follow the SDS for respirable dust limits.
Its plates form overlapping layers that slow the diffusion of water, oxygen and ions through the film, reinforcing barrier protection.
Yes. As an extender it lowers gloss and can create a sandable, matte surface, which is useful in primers and surfacers.
