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Historic Preservation - Technical Procedures

Spectitle:

Primers And Paints For Zinc And Galvanized Iron And Steel

Procedure code:

0501015S

Source:

Us Custom House, New Orleans, La - Fromherz Engineers

Division:

Metals

Section:

Metal Materials

Last Modified:

02/24/2012

Details:

Primers And Paints For Zinc And Galvanized Iron And Steel



PRIMERS AND PAINTS FOR ZINC AND GALVANIZED IRON AND STEEL


This standard includes general information on primers and paints to
be used on interior and exterior zinc and galvanized iron and
steel.

THE SELECTION OF A SUITABLE PRIMER AND PAINT FOR METALS DEPENDS ON
MANY FACTORS INCLUDING THE TYPE OF METAL TO BE COATED, THE TYPE OF
SURFACE PREPARATION TO BE USED, ENVIRONMENTAL AND SURFACE
CONDITIONS, DESIRED APPEARANCE AND PERFORMANCE REQUIREMENTS,
METHOD OF APPLICATION, AND TYPE AND LEVEL OF EXPOSURE.  CONSULT A
PAINT MANUFACTURER ALONG WITH THE REGIONAL HISTORIC PRESERVATION
OFFICER BEFORE MAKING THE FINAL SELECTION.

Features which can be made from zinc or galvanized iron and steel
include gutters and downspouts, flashing, roofing tiles, crestings
and other decorative roofing features, and miscellaneous decorative
features made from pressed or folded metal sheets.

Galvanizing is the process of coating steel with zinc to protect it
from corrosion.  Three methods of galvanizing includes hot-dip
galvanizing, electrogalvanizing and cold galvanizing.  Galvanized
steel may be painted for many reasons, but the most important
reason is to provide additional corrosion resistance.

The primary purpose of paint is to protect the metal from rust and
corrosion.  To do so, paint manufacturers have developed paint
systems which are made to work together to protect the substrate.
These systems include primers and appropriate, compatible top coats
which can vary depending on the substrate and can vary between
manufacturers.  As a result appropriate primers and compatible top
coats, both from the same manufacturer should be used.

For information on paint removal, surface preparation and
application procedures, see the following:

-    For guidance on paint removal from wrought iron, cast iron and
    steel, see 05010-05-R, 05010-16-R, and 05010-17-R.

-    For guidance on preparing metal surfaces for painting, see
    05010-05-R, 05010-16-R and 05010-17-R.

-    For additional information on the history, properties and uses
    of paint, see 09900-01-S.

-    See 09900-07-S for general guidelines on painting interior and
    exterior surfaces.

-    For general information on galvanized iron and steel, see
    05010-09-S.  Much of the same information will also be
    applicable to pure zinc.


***PRIMERS FOR ZINC, GALVANIZED IRON AND STEEL***

TYPES

Oil/Alkyd Primers:  Oil-based primers are to be used ONLY ON OLD
AND/OR BADLY RUSTED SURFACES WHICH NO LONGER HAVE
ANY GALVANIZED COATING.

- Advantages: None.  Not generally recommended for use on
 galvanized metal.

- Limitations:

 1. May react with the zinc coating on the steel to cause poor
    adhesion.
 2. Generally not recommended for use on galvanized surfaces
    unless extremely rusted or weathered.

- Products/Suppliers:
 1. Benjamin Moore, #155 Ironclad Retard Rust Inhibitive Paint
 2. Red Devil, #9 Iron Oxide Primer
 3. Sherwin-Williams, E41 N1, Kromik Metal Primer
 4. Rust-Oleum, #7769, Rusty Metal Primer, or #5769, Red
    Primer.


Zinc-rich Primers:

- Advantages:
 1. Recommended for welded or damaged areas.
 2. Recommended for spot priming clean areas - areas where the
    galvanized coating is missing or badly rusted.
 3. Good resistance to salt water.
 4. Normally used to protect steel from corrosion.
 5. May be used on iron.

- Limitations: None.

- Products/Suppliers:
 1. Rust-Oleum, #7785, Zinc Sele - use only latex top-coat.
 2. #770 Galvanized Metal Primer - use only latex top-coat.


Latex Primers:

- Advantages:
 1. Good adhesion.
 2. Free of grease or oil.
 3. Good results on interior surfaces with no unusual
    atmospheric conditions.

- Limitations:
 1. Not suitable for use in areas of high humidity or extreme
    temperature changes.

- Products/Suppliers:
 1. Sherwin Williams, A-100, B42 N8, or Super paint series.


***PAINTS FOR ZINC, GALVANIZED IRON AND STEEL***

TYPES

 The paint selected must be from the same manufacturer and made
 to be used with the primer selected.  It should also be selected
 for use in a specific situation where applicable.

- Intermediate and Top Coats:  For the intermediate and top coat,
 use a paint from the same manufacturer as the prime coat, and
 one that is made to be used with that primer.  Either oil-based
 or latex paints may be used as recommended by the paint
 manufacturer.  

 Apply using a brush to insure complete coverage.  

- Allow the intermediate coat to dry according to manufacturers
 instructions before applying the final top coat.

                         END OF SECTION