Finishes and corrosion protection

It is not normal practice to grind welds unless appearance is critical.

Structural welds are not usually ground down since the process adds unnecessary expense to the construction costs. Where required for aesthetic reasons, it is possible to grind butt welds flush with the adjacent plates, provided the weld is a straight butt. Other butt welds (called 'K' welds) cannot be ground because the fillet at the side of the weld acts as a reinforcement. Obviously grinding is not possible for fillet welds, because any grinding will cut away the connecting metal.

A variety of corrosion protection systems can be used for bolts.

All bolts, i.e. grade 4.6, grade 8.8 and HSFG bolts, are available in a variety of finishes as follows:

• Black: With no corrosion protection, and either a black surface of mill scale, or a lightly rusted surface where the scale has come off.
• Sheradized: A thin coating of zinc dust is deposited on the bolt. This gives limited corrosion protection until paints are applied. The zinc adheres well to the bolt.
• Galvanized bolts have reasonable thickness of zinc, but are somewhat difficult to paint on site.
• Plated bolts: Zinc and cadmium plating are used, and have properties similar to galvanized bolts. The process is easier than galvanising, but gives a more brittle coating.
• Corten bolts: These are available to special order, and they have similar properties to other Corten material.

Stainless steel bolts are not usually used for the main structural frame. They might be used where components of the frame itself are of stainless steel, but not otherwise, because stainless steel can set up a galvanic cell when in contact with normal steel used for structural work. If stainless steel bolts have to be used in conjunction with a normal steel frame, separating washers (usually neoprene) must be used to keep the two materials apart.