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Galvanized bolts are a special type of hardware designed to outperform nails and screws in many applications. They feature heavy-duty construction that allows them to support heavier loads than a nail or screw, as well as a special coating that helps prevent damage from rust or corrosion. Galvanized bolts can be used to join wood or steel, and are found in everything from bridge construction to residential decks.
Like many types of fasteners, galvanized bolts are made from steel, which is susceptible to rust when exposed to moisture or chemicals. By applying a special zinc coating to the bolt, manufacturers extend its life along with its strength and durability. Galvanizing also allows the bolt to be used in a much wider variety of applications due to its increased performance.
The galvanizing process actually consists of a series of chemical reactions. Initially, the bolt is coated with hot zinc, which acts as a barrier between steel and any potentially corrosive elements. Zinc oxide is formed when the zinc coating reactions with oxygen in the atmosphere. When carbon dioxide reacts with the zinc oxide, zinc carbonate is formed. This zinc carbonate layer protects the bolt from corrosion and rust.
Galvanized bolts can be distinguished by their crystallized, spangled surface. These bolts are primarily used in outdoor applications, where rain and moisture prohibit the use of standard steel fasteners. They are also used in coastal areas or marine settings, where salt water exposure can quickly corrode untreated steel. Finally, galvanized bolts are found in industrial settings, where chemical exposure will often damage other fasteners.
These bolts are available in two basic varieties, which can be categorized by how they are installed. Lag bolts are used when only one side of an object is accessible. The bolts are installed in an object using a socket wrench, and a washer is placed between the head of the bolt and the face of the object to prevent damage. When both sides of an object are accessible, carriage bolts are used. The carriage bolt is inserted through the front of the object, then a washer is added to the tail end of the bolt for added strength and support.
Galvanized bolts are typically more expensive than uncoated varieties, but their additional strength may reduce future maintenance and repair costs. They must always be used with a galvanized washer, as uncoated washers can compromise the strength of the installation. Finally, installers should take care when welding or cutting galvanized metals, as this could release toxic fumes or harmful particulate matter into the air.
A word of warning when building a deck from ACQ treated lumber. This type of lumber contains no arsenic, so it's safer to use, but it is also more corrosive, so don't use galvanized screws. We did and our deck collapsed.
We were told by a friend who works in construction to use the hot-dipped galvanized screws to avoid corrosion and collapse. We did just that, and our deck is still standing. I think the ACQ lumber contains copper that is corrosive to other metals.
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