Can you recommend some products for masking hot-dip galvanized steel?

Masking products are applied to specific areas of steel when the galvanized coating on those areas would interfere with the end use of the product (such as on faying surfaces), or when additional work needs to be done on masked areas and a galvanized coating would make the work more difficult or expensive (such as on areas that will be welded or on fasteners that cannot have any additional width from a zinc coating). Of course, any time steel is masked, there will be no corrosion protection of the steel in those areas. The unmasked areas will not affect the corrosion protection of the galvanized coating in other areas to any large extent. 

Many different types of materials have been used to mask steel during hot-dip galvanizing. High temperature paints used for masking are applied to flat surfaces that require the absence of a galvanized coating. The most common application of this is when areas of the steel are to be welded after galvanizing, such as stud welding. The paints can be removed after galvanizing by grinding or brushing, depending on the size of the area that has been masked. Greases and pastes that are resistant to the conditions of the galvanizing process are typically used on internal threads or threaded holes. When pastes are moistened with a little water, they can be pressed into holes and openings; it is essential that care is taken not to trap air in these holes. The paste hardens with the heat of galvanizing and prevents ingress of zinc. It will then be necessary to remove the residue after galvanizing by means of brushing. Adhesive tapes are used on cylindrical components, such as threaded bolts or pins. The tape carburizes in the galvanizing kettle and the residue that remains prevents the galvanizing reaction from occurring. This residue must be removed after galvanizing by using a stiff bristled brush. Another method of masking used to prevent unwanted coating on internal threads or clearance holes is the use of filler bolts or pins. A bolt or pin is greased prior to insertion in the hole and removed after galvanizing. Heat may be required to remove the bolt or pin as the zinc coating may lock the bolt or pin in place.

What Works?

Some products are more effective than others and the price range of the products varies substantially, depending on if the product was designed specifically for use during hot-dip galvanizing.A few products specifically designed for masking during hot-dip galvanizing include:

• Stop Galv (Transtrade 918-521-7271)
• Maskote Zinc Stop-Off (Pyrotek 440-669-2930)
• Galva Stop (Puma Chemical 800-211-7993)

Because the above products have been specially formulated for use during galvanizing, which sometimes required additional engineering of the products, they tend to be more expensive than other materials used to mask steel. Other products that have worked well at masking steel during hot-dip galvanizing, but that were not designed specifically for this use, include:

• GE 100% Silicone Caulk (Home Depot, Lowes)
• DAP Household Adhesive Sealant (Home Depot, Lowes)
• NAPA RTV Red (NAPA Auto Parts)

Products not designed specifically for hot-dip galvanizing tend to be less expensive than products designed specifically for use during hot-dip galvanizing, but sometimes do not work as effectively; however, each of these products did perform well during testing conducted by American Galvanizers Association. Regardless if the products used for masking steel were designed specifically for hot-dip galvanizing or not, it is important to always follow the manufacturers recommendations and Material Safety Data Sheets. Speaking of testing, the results of the AGA study on masking materials are now available. The information has been compiled into a white paper that discusses testing on a total of 15 different materials used for masking steel during galvanizing. View the Galvanizing Note, Masking Materials for Preventing Hot-Dip Galvanizing for more information.