In cold weather, tar usually becomes thicker, stiffer, slower to spread, slower to settle, and less able to flow into small surface cracks.
Cold makes tar less mobile. A product that brushes easily on a warm day can become thick and reluctant in a cold workshop or shed. This happens because the heavy oily and resinous parts of the tar flow more slowly as temperature drops.
Cold application can affect performance. If tar cannot wet the surface properly, it may sit unevenly, leave ridges, or fail to reach small cracks and fibres. It may also take longer for any lighter fractions to leave the coating, so the surface remains tacky or patchy for longer than expected.
Cold timber introduces another problem: moisture. A surface that looks dry can still hold condensation or dampness, especially when moved from cold air into warmer air. Tar does not bond well to a dirty, icy, or wet surface. It may trap moisture rather than protect against it.
Cold weather does not make tar useless, but it makes timing and surface condition more important. Tar behaves best when it can spread, wet the surface, and settle in a stable environment rather than fighting frost, condensation, and stiff material.