Caulk

The oldest form of caulk consisted of fibrous materials driven into the wedge-shaped seams between boards on wooden boats or ships.

Traditional caulking (also spelled calking) on wooden vessels uses fibers of cotton and oakum (hemp) soaked in pine tar.

In the Hebrew Bible, the prophet Ezekiel refers to the caulking of ships as a specialist skill.

[4] Caulking of iron and steel, of the same type described above for ship's hulls, was also used by boilermakers in the era of riveted boilers to make the joints watertight and steamtight.

These are used in caulking guns, which typically have a trigger connected to a rod which pushes the plunger, and has a ratchet to prevent backlash.

[7] Closed-cell rod will also lose firmness and out-gas if damaged during installation or overcompressed or at sharp bends.

The gasses cannot pass through this backer rod and can deform, weaken, and even cause holes (leaks) in the caulk or sealant as it escapes.

[9] Not only is acrylic latex inexpensive, but it is also the easiest type to apply smoothly and later paint if needed.