In freezing conditions, tar becomes much stiffer and may not spread or bond well. Existing tar coatings can survive freezing, but water in cracks and beneath the coating can cause damage.
Freezing temperatures slow tar almost to a standstill. Thick tars can become hard to brush, hard to pour, and poor at penetrating wood. If the surface is icy or frosted, the tar may bond to the frost layer rather than to the actual material beneath it.
A cured or weathered tar coating is usually less troubled by cold itself than by water. If moisture has entered cracks, end grain, joints, or gaps under the coating, freezing expansion can widen those openings. The tar may then crack, lift, or lose contact with the surface.
Freeze-thaw cycles are worse than one cold spell. Repeated wetting, freezing, expanding, thawing, and drying puts stress on timber and coatings. Tar can remain flexible enough to tolerate some movement, but it cannot repair poor drainage, open joints, or trapped water.
In simple terms, tar can live through freezing weather, but freezing conditions are a poor time to ask fresh tar to perform perfectly. The best results come when the surface is dry, clean, and warm enough for the tar to wet it properly.