Choosing Black or Galvanized Anchor Bolts

Anchor Bolt Source

Depending on the requirements of the project, customers can order anchor bolts in either black or galvanized finish. The difference between the two is that "black" (also called plain) construction fasteners are unfinished fasteners that are not coated. There are instances where the fasteners do not need to be galvanized. Galvanizing refers to an anchor bolt that has been dipped in molten zinc to coat the entire fastener. The zinc outer coating is for those anchor bolts that are going to need protection from corrosion. This happens when water or moisture is introduced to the anchor bolt on a regular basis. The zinc outer coating acts as a repellent and a first defense against moisture. Galvanizing is also favored as a means of protective coating because of its low cost, ease of application and relatively long life. For fatigue critical anchor rods, corrosion protection is particularly important, since corrosion pitting can degrade the fatigue resistance of the bolt. Typically when anchor rods, nuts and washers are used outdoors galvanizing should be considered. Hot dip galvanizing should be according to ASTM A153 Class C or mechanically deposited by ASTM B695, Class 50 and should be specified by the purchaser.  At Anchor Bolt Source we typically provide hot dip galvanizing to ASTM A153 Class C.  The hot dip process provides a heavier zinc coating than mechanical galvanizing as well as a longer life.  To ensure a good fit with the heavier zinc coating, it is a good idea to ship the nuts assembled to the anchor rods and determine that the nuts run down the threads.  

For more information about anchor bolts, anchor rods or embedded steel, please visit Anchor Bolt Source.