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Caulking

Silicone caulking being demonstrated.

Caulking is a process used to seal the seams in wooden boats or ships, and riveted iron or steel ships, in order to make them watertight. The same term also refers to the application of flexible sealing compounds to close up crevices in buildings against water, air, dust, insects, or as a component in firestopping.

Traditional caulking (also spelled calking) on wooden vessels uses fibers of cotton, and oakum, which consists of pieces of hemp fiber soaked in pine tar. These fibers are driven into the wedge shaped seam between planks with a caulking mallet and a chisel-like device called a caulking iron. The caulking is then covered over with a putty in the case of hull seams, or in deck seams with melted pine pitch in a process referred to as paying.

Modern marine sealants are frequently used now in place of the pitch, or even to supplant the oakum and cotton itself.

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 had the effect of displacing the metal into a close fit with the adjoining piece.^[1] This is an application of the metalworking process known as "upsetting". Originally done by hand much like wooden vessel caulking, pneumatic tools were later employed. With the advent of electric-arc welding for ship construction, steel ship caulking is truly a lost art.

The same technique described above for making riveted steel or iron ships watertight was also used to make riveted boilers, such as steam locomotive boilers, watertight and steamtight.^[2]

A United States Air Force airman applying silicone caulk to baseboard

Caulk (calk) can refer either to the caulking substance or to the process of applying it. Caulking as a term has spread to the building trade, meaning the activity of closing up joints and gaps in buildings. The function of caulking is to provide thermal insulation, control water penetration and noise mitigation.

This is mostly done with ready-mixed construction chemicals sold as caulk such as silicone, polyurethane, polysulfide, sylil-terminated-polyether or polyurethane and acrylic sealant. Unlike construction caulk, which is applied where no building movement is expected, a sealant is made of elastomeric materials that typically allow movement of 25% to 50% of the width of the joint. Silicone sealants form a durable, water-tight seal, but are not typically paintable. Some silicone sealants are made to be paintable with certain types of paint such as water or oil-based paints. Other sealants are paintable.

One-component sealants are commonly sold in cartridges which are loaded into a pistol-like caulking gun (opening at the side) or barrel gun (opening at the end) for application. During the tool-working time, which varies by chemistry, the bead can be pressed into the joint so that it can bond with the materials on both sides, and also be smoothed. The time it takes for a chemical sealant to become a rubber is known as the curing time and varies by temperature and humidity. Issues of technique that may not be obvious to first-time users:

• The nozzle must be chopped short to match the intended size of the bead. If the opening in the nozzle is too small, the bead is liable to bunch and is difficult to keep even.
• Common tools are a pointing tool, shaped wood, wet finger or a spoon. Detergent should not be added to the moisture for tooling since it may drip onto the bond surface causing a loss of adhesion.
• For neat work, the worker may apply painter's masking tape beforehand, taping off the areas on each side of the joint to catch any surplus, and remove the tape again before the tooling time has expired.
• To prevent three-sided adhesion or to avoid sag in wide, deep joints, a backer rod made of plastic foam can be pressed into the gap before caulking.

Backer rod can also be used to fill cracks in sidewalks, and other masonry before caulking. It is composed of a foam roll that is generally about 1/4 inch to 1 1/2 inch thick. The material is stuffed into the cracks to be sealed and then caulked over.

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Caulking

1. ^ U.S. Coast Guard: Navigation and Vessel Inspection Circular Number 7-01: Procedures for hull inspection and repair on vessels built of riveted construction. Issued 2001-10-09.
2. ^ Colvin, Fred H. (1906). The railroad pocket-book: a quick reference cyclopedia of railroad information. New York, Derry-Collard; London, Locomotive Publishing Company (US-UK co-edition), page C-9. 

• Standards Association of New Zealand, Glossary of Building Terminology, 1979. ISBN 0-473-00035-0
• Recommendations for Selecting and Using Caulks and Sealants in Pest Management (PDF)
• How to use a caulking gun