Definition
A piece of loose-weave cloth lightly impregnated with a sticky, non-drying resin or varnish, used to wipe a surface immediately before painting or finishing in order to pick up dust, lint, and fine particles that would otherwise become trapped in the new finish.
Plain English
A slightly sticky cloth used to wipe a surface clean of dust just before paint or other finish is applied, so the dust does not end up stuck in the paint.
Context Anchor
Seen in aircraft maintenance, especially during surface preparation before painting or applying a finish.
Derivation
The word 'tack' here means slightly sticky or adhesive — the same sense used when a finish is described as being 'tacky' before it fully dries. A tack rag is literally a 'sticky rag,' named for the feel that lets it grab dust off a surface.
Why Pilots Care
A clean surface is essential for paint adhesion; poor preparation leads to finish defects that can affect aerodynamics, corrosion protection, and inspection results.
Analogy
It works a little like a lint roller for a surface before painting: the slight stickiness grabs small particles instead of just pushing them around.
Intuition Check
A tack rag is not used to spread paint, glue, or cleaner. It is used to pick up loose dust and fine particles before finishing.
Example Sentence 1
Before spraying the primer, the technician wiped the wing skin down with a tack rag to lift off any remaining dust.
Example Sentence 2
After the fuselage was masked, a fresh tack rag was used on every panel to ensure the topcoat would have no lint trapped beneath it.