Caulk
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Caulk (also known as caulking and calking)<ref>Template:Cite dictionary</ref> is a material used to seal joints or seams against leakage in various structures and piping.
The oldest form of caulk consisted of fibrous materials driven into the wedge-shaped seams between boards on wooden boats or ships. Cast iron sewerage pipes were formerly caulked in a similar way. Riveted seams in ships and boilers were formerly sealed by hammering the metal.<ref>Template:Cite book</ref>
Modern caulking compounds are flexible sealing compounds used to close up gaps in buildings and other structures against water, air, dust, insects, or as a component in firestopping. In the tunneling industry, caulking is the sealing of joints in segmental precast concrete tunnels, commonly by using concrete.
Historical uses
Traditional caulking (also spelled calking) on wooden vessels uses fibers of cotton and oakum (hemp) soaked in pine tar. These fibers are driven into the wedge-shaped seam between planks, with a caulking mallet and a broad chisel-like tool called a caulking iron. The caulking is then covered over with a putty, in the case of hull seams, or else in deck seams with melted pine pitch, in a process referred to as paying, or "calefaction". Those who carried out this work were known as caulkers. In riveted steel or iron ship construction, caulking was a process of rendering seams watertight by driving a thick, blunt chisel-like tool into the plating adjacent to the seam. This displaced the metal into a close fit with the adjoining piece.<ref>Template:Cite web</ref>
Caulking of iron and steel was also used by boilermakers in the era of riveted boilers to make the joints watertight and steamtight.<ref>Template:Cite book</ref>
Modern use in construction
Application
For bulk use, caulk is generally distributed in disposable cartridges, which are rigid cylindrical cardboard or plastic tubes with an applicator tip at one end, and a movable plunger at the far end. 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. The push rod may also be actuated by a motor or by compressed air. Similar mechanisms are used for grease guns.<ref name="McClintock 2011">Template:Cite news</ref>
For smaller applications, caulk may be distributed in squeeze tubes.<ref name="McClintock 2011" />
Backer rod
Backer rod, also called backer material or back-up rod, is a flexible foam product used behind caulking to increase elasticity, reduce consumption, force the caulking into contact with the sides of the joint creating a better bond, determine the thickness of the caulking, and define the cross-section hour-glass shape of the caulk. The backer rod also acts as a bond breaker to keep the caulking from sticking to the bottom of the opening—called a three-sided bond—with the caulk only adhering to the sides of the opening in an hour-glass shape it can flex more easily and is less likely to tear.Template:Citation needed
Closed-cell foam does not absorb water and is impermeable. Closed-cell rods are less compressible and should not be compressed more than 25%.<ref name="Gibb 1980 p41">Template:Cite magazine</ref> 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.
Out-gassing is the reason that open-cell backer rod was developed.<ref name="Gibb 1980 p41" /> Open-cell foam is porous so it will let gasses through which could otherwise cause blistering of the caulk or sealant. Additionally, open-cell backer rod allows air to get to the back side of the caulk or sealant which accelerates curing when used with air-cured sealants such as silicone. Open-cell rod is more compressible than closed-cell foam and should be compressed 25% to 75%.<ref name="Gibb 1980 p41" />
Energy efficiency
According to the Consumer Federation of America, sealing unwanted leaks around homes is an excellent way to cut home energy costs and decrease the household carbon footprint.Template:Citation needed
Preventing infestation
Sealing cracks and crevices prevents ingress by rodents.<ref>Template:Cite web</ref>
Types
Acrylic latex
The most common type of caulk is acrylic latex, for general-purpose use.<ref name="Dale 2023">Template:Cite web</ref> Not only is acrylic latex inexpensive, but it is also the easiest type to apply smoothly and later paint if needed.<ref>Template:Cite web</ref><ref name="Epic Rope 2019">Template:Cite web</ref>
Acrylic tile sealant
Acrylic tile sealant usually comes in small tubes and is commonly used for wet applications.<ref name="Epic Rope 2019" />
Polyurethane
Polyurethane caulk is very durable construction sealant. It has good adhesion towards concrete, wood, metals (steel, aluminium), plastic, masonry etc.<ref>Template:Cite web</ref> It's commonly used for sealing ventilation systems.<ref>Template:Cite book</ref>
Silicone
Silicone caulk or sealant is water-, mold-, and mildew-resistant.<ref name="Dale 2023" /><ref name="Epic Rope 2019" /> Technically, when a joint material is silicone-based, it is considered a sealant rather than caulk.<ref>Template:Cite web</ref>