Information and Specifications


Table of Contents

I. Introduction
II. Scope
III. Definitions
IV. Detailed Requirements

  • Base Metal
  • Processing
  • Corrosion Protection
  • Porcelain Enamel Finish
  • Flatness of Panel
  • Clips and Attachments

V. Test Methods
VI. Compliance and Guarantee
VII. Supplementary Considerations

I. Introduction

This standard is based on the experiences and recomendations of architectural porcelain enamel manufacturers and other technical authorities from the porcelain enameling industry. It has been adopted as a PEI Tentative Standard by the Standards Committee, specification authority for the Porcelain Enamel Institute, Inc.

II. Scope

The specification applies only to architectural porcelain enamel on substrates. It does not cover the types of panels, the metal fabrication, or the assembly of finished units.

III. Definitions

A. Porcelain Enamel

Porcelain enamel is a substantially vitreous, or glassy, inorganic coating bonded to metal by fusion at a temperature above 1000 degrees F (538 degrees C).

B. Architectural Porcelain Enamel

An architectural porcelain enamel is one that is used as a facing material or as a component on any building structure. When signs are an integral part of the facing material, the finish used on the sign is considered as an architectural porcelain enamel.

C. Steel

For the purposes of this specification, steel is defined to include:

1. Special purposed “enameling iron or steel” of low metalloid and copper content, expecially manufactured and processed for the production of porcelain enamel units for architectural purposes. (See PEI-201, Manual for Selection of Porcelain Enameling Steels.)

2. Conventional cold rolled sheets which can be satisfactorily porcelain enameled and which meet other requirements of this specification. Note: Warpage may be a significant factor when using cold rolled steel as it impacts Section IV, E.

IV. Detailed Requirements

A. Base Metal

Base metal shall be in accordance with the definition under the definition of steel.

B. Processing

A porcelain enamel coating shall be applied to all areas of each unit, including back and flanges, by methods recognized as good commercial practice.

At least one additional fired coating shall be applied to the face side of each unit.

C. Corrosion Protection

The back side of non-laminated panels shall be protected with fired porcelain enamel coating.

The coating requirements for the back side do not apply when adequate corrosion protection is provided to the panel by the laminated construction.

Corrosion protection in laminated panels is dependent upon the durability of the lamination. A test method which has been widely used for determining the resistance of sandwich panels to severe exposure conditions is described in ASTM C481-61T.

D. Porcelain Enamel Finish

1. Weather Resistance
The porcelain enamel finish on all surfaces exposed to weathering shall pass the acid spot test as given in the Test Methods section. In addition, all red, yellow and orange porcelain enamels shall pass the cupric sulfate test as described in the same section.

2. Continuity of Coating
Visual inspection of each piece shall reveal no visible breaks or surface defects in the cover coating that will expose the underlying coating or the steel on surfaces exposed to weathering, nor the underlying steel on either the back or flanges. This requirement shall not apply to sheared edges.

Special metallic coatings are sometimes fired onto porcelain enamel surfaces to achieve specific textures and finishes. This coating may be continuous or may have purposely induces breaks and discontinuities. Such coatings shall qualify under this requirement if the underlying porcelain enamel satisfies all requirements in this specification.

3. Surface Appearance
The porcelain enamel on all surfaces exposed to weathering shall be free of blemishes in the coating that my impair the serviceability or detract from the general appearance of the panel when viewed from a distance of 5 feet or the distance at which the panel will be normally viewed, whichever is the greater. Orange peel and surface finish should be reviewed and agreed on before production. Color tolerances should be agreed on before production. Certain colors are more susceptible to color stability.

E. Flatness of Panel

Finished faces shall have a maximum variation of 3/16″ (4.76mm) in a convex direction when measured perpendicular to the nominal plane of the panel face. Variation in the concave direction shall be limited to 3/32″ (2.38mm) from actual plane of the panel face.

These tolerances are for panels with a face area of 8 sq. ft. (0.86 m2) or less. Proportionately greater allowance will be permited for panels of greater areas. Panels are to be measured in the position (usually vertical) in which the panel will eventually be installed. Note: While not a part of the specification itself, further data regarding flatness is set forth in the Section, Supplementary Considerations.

F. Clips and Attachments

All metal lugs, clips and other attachments fastened to the panel, as well as those furnished unattached by the manufacturer, for the purpose of attaching the panel to the building structure shall be made of a recognized corrosion resistant metal such as stainless steel type 302 or equivalent. This requirement specifically excludes stiffener bars or braces, clips for holding insulation in place, and similar devices not intended for the purpose of attaching the panel to the building structure. Also excluded are furring, substructure assemblies, or braces that may be furnished by the manufacturer.

V. Test Methods

A. Acid Spot Test

1. Treatment of Specimen

Wash the specimen with soap and water, rinse thoroughly, then dry with a clean cloth by blotting (not rubbing). Immediately after washing, and with the specimen at 80 +- 10 degree F (26.6 +- 5 degree C) place several drops of a 10% citric acid solution (also at 80 +- 10 degree F). On the specimen to form a pool and immediately cover with a 1″ inverted watch glass. The acid solution shall contain 100 grams of citric acid per liter of water and shall be prepared not more than 48 hours prior to use. After 15 minutes of treatment, remove the watch glass and rinse the acid solution from the surface. Dry the specimen with a clean cloth by blotting (not rubbing).

2. Blurring-Highlight Test

This test shall be made in a well-lighted location. Hold the specimen so that the image of a small light source, such as a frosted lamp bulb, is observed as a highlight in the untreated area, the line of vision with 45 degree of the perpendicular to the surface. (A desk lamp is recommended for this purpose.)

Focus the eyes on the image of the light source, not on the enamel surface. Then shift the specimen just sufficiently to bring the image of the light source into the treated area, observing it as it passes across the boundary line between the two areas. Any color difference in the enamel due to staining shall be ignored, but if a definite blurring of the image is observed as it passes from the untreated to the treated area, the enamel shall fail the acid spot tests.

3. Wet-Rubbing Test
If there is no blurring of the highlight, place 4 or 5 marks on the treated area with a No.1 pencil using a firm pressure. Next, rub these marks vigorously with a clean cloth that has been dipped in water and tightly twisted to eliminate the excess. If the marks are removed completely by this wet-rubbing treatment, the specimen passes the test; otherwise it fails.

The testing procedures outlined above are the same as those specified in PEI T-21, “Test for Acid Resistance of Porcelain Enamels (Citric Acid Spot Test)”, a standard of the Porcelain Enamel Institute and ASTM C282.

Porcelain enamels that pass the tests would be graded wither Class AA or Class A by the standard test procedure.

B. Cupric Sulfate Test for Red, Yellow and Orange Porcelain Enamels

Place a few drops of a saturated solution of cupric sulfate [prepared by placing 50 gms. of cupric sulfate (CuSO4.5H2O), reagent grade, in 100 ml. of distilled water and aging for 16 hours or longer] on the porcelain enamel surface to be tested. Cover the small pool of solution with a 1″ inverted watch glass and place the specimen in a controlled illumination environment equivalent to that described below. After 20 hours at room temperature, remove the watch glass, rinse the test area with water, and dry with a clean cloth. Visually examine the treated area immediately. If any darkening can be detected visually, the specimen fails the test. Changes in gloss caused by the treatment shall not be considered in the grading.

This test is fully described in PEI T-22, “Cupric Sulfate Test for Color Retention”, a tentative standard of the Porcelain Enamel Institute. The apparatus for control of illumination consists of a light source and enclosure. The light source shall be a 100-volt, 15 watt white, fluorescent lamp, 1″ diameter by 18″ long. The enclosure, made of plywood or other suitable material, shall be 10″ long, 6″ wide and 12″ high (inside dimensions). It shall be painted white on the inside and vented for air circulation. Venting is accomplished by 11 1/2″ holes, drilled 1″ apart on a centerline 1″ from the inside top, and 11 similar holes drilled on a centerline 1″ from the bottom on each of the two long sides. The lamp is centered near the inside top of the enclosure in such position that the distance between the specimen surface and the centerline of the lamp is 9″.

VI. Compliance and Guarantee

A. Compliance Statement

Manufacturers shall certify in writing at time of submission of a bid that the porcelain enameling will be performed in accordance with the current edition of the Manual for Architectural Porcelain Enamel (PEI-1001) as issued by the Porcelain Enamel Institute.

B. Guarantee

All porcelain enamel for architectural purposes manufactured for projects giving references to these specifications shall meet these specifications in every respect except where specifically stated. Any further guarantee shall be made by the manufacturer in accordance with his standard practice.

VII. Supplementary Considerations

The following, while not a part of the specification, are set forth as an aid to those specifying architectural porcelain enamel.

A. Gloss

The gloss of the porcelain enamel finish, together with permissible tolerances in gloss, should conform visually with samples selected by the architect and/or purchaser during negotiation of the contract. When porcelain enamels of especially low specular gloss are agreed upon, however, difficulties may be encountered in applying the acid spot test. An acid resistance test that has been found useful in predicting the weather resistance of porcelain enamels of this type is the boiling acit test given in ASTM C283. Experience has shown that if the measured weight loss is 12 mg./in.2 or less, the enamel will have good weather resistance.

It is also recommended that the finish be of a type that will not reflect distinct images. If the reflecting power is high, images seen in the mounted panels will usually be distorted due to even very small deviations from flatness. Experience has shown that the overall appearance of a structure will be considerably improved if the image reflection (distinctness-of-image gloss) is kept as low as possible. A qualitative evaluation of this type of gloss can be made by observing the image of a window mullion in the surface of the panel. If the image is clear and sharp, the distictness-of-image gloss is normally too high for architectural purposes. Reproducible, quantitative measurements of image-gloss can be made using the equipment and procedure described in PEI T-20, “Image Gloss Test”, a standard of the Porcelain Enamel Institute.

B. Color

The color and color tolerance should be specified in the purchase contract. If possible, this should be based on porcelain enameled sample color specimens. Compliance with color specification may be determined by visual matching under viewing conditions mutually agreed upon by the contracting parties, or may be determined instrumentally.

The color tolerance to be specified should depend upon the color service requirement and the ease with which particular color or colors can be controlled in production, and should be clearly specified in the purchase contract. To be considered also are the type of structure, the texture of the finish, and the proximity of adjacent panels. Some colors can be controlled more closely than others.

Decorative colors and coloring processes, such as stenciling, silk screening and highlighting, may be used to produce designs, letters and special effects, provided the finish so produced meets all of the requirements of this specification

C. Texture

Unless otherwise specified in the contract, the porcelain enamel will be furnished in a smooth and non-textured finish. Orange peel tolerance should be specified with tolerance samples.
Special textures and finishes should be in accordance with samples agreed upon during contract negotiations. In all other respects, special finishes shall conform to this specification.

D. Thickness of Porcelain Enamel

Various thicknesses are encountered in commercial ware. Thickness tolerance should be agreed upon in writing before production. Texture, color and processing techniques influence the amount of porcelain enamel which is applied.

Thin porcelain enamel coatings are desirable to provide maximum resistance to damage from flexure. However, processing methods and desired appearance characteristics may result in variations of recommended minimum thickness of the coating. A minimum of 0.0035″ (0.089 mm) of cover coat will normally provide acceptable durability. The total thickness may range from 0.005 to 0.020″ ().127-0.508 mm), depending upon process and appearance.

Total thickness should not exceed 0.020″ (0.508 mm), except where greater thicknesses are necessary to meet specific appearance requirements.

E. Thickness of Metal

Thickness, grade and design tolerance of metal should be agreed upon during negotiation of the contract. Full consideration should be given to the size, shape or detail of the unit, and the duty which the unit is to perform in the building structure. (see PEI-101, Manual of Design and Fabrication of Metal for Porcelain Enameling.)

F. Packaging and Shipping

Packaging, shipping and handling methods should be specified and should be practical for supplier, shipper, and erector.

G. Shop Drawings

Complete drawings should show forming detail, tolerances allowed (both dimensional and flatness), location in completed structure, and on-the-job cutting or drilling requirements. The maximum allowable extent of damage due to drilling and cutting should be agreed upon by contracting parties.


Mechanical & Physical Properties

(PEI Bulletin #502)

Surface Hardness | 3.5 to 6 (Moh’s Scale) | ——
Abrasion Resistance | Excellent | C448
Compressive Strength | 20,000+ psi | ——
Modulus of Elasticity | 10 x 166 | ——
Ultimate Strength(steel) | 50,000 psi | A424-62T
Yield Strength(of steel) | 35,000 psi | A424-62T
Thermal Expansion | 8-14 x 106 cm/cm/-C | C359


Chemical Properties

(PEI Bulletin #503)

Salt Spray | Excellent | B117-571
Organic Solvents | Superior | ——
Acids | Class A | C282/C283
Alkali | Max.pH of 12 @ 212-F(100-C) psi | C614
Water | 190-(88-C) Continuous service | ——
Oil | Not affected | ——
Soil Corrosion | Not affected | ——


Appearance Properties*

(PEI Bulletin #501)

Color permanence, Gloss retention, Cleanability
Superior weatherability as evidenced by extensive testing by the National Bureau of Standards (NBS) and the Porcelain Enamel Institute (PEI) at a variety of sites over a period of 30 or more years.

*Class A acid resistance porcelain enamel