Metal Building Article: Watch The Washer

WATCH THE WASHER
HOW TO INDENTIFY A QUALITY WASHER AND WHY IT MATTERS

FOR MANY YEARS PEOPLE have accepted that if a screw has a washer, it will do the job. Unfortunately in today's price driven market, this is no longer always true.

To fully understand why you need to be able to identify and use quality washers, it's important to know how a washer works in a complete roofing and cladding system. A washer must withstand all environmental conditions, including UV degradation, acid rain and extreme temperatures while remaining elastic, intact and watertight.

Unfortunately, washers often are overlooked because of their minor cost per unit compared to fasteners and steel sheet. Washers make up less than one-one-thousandth of 1 percent of the cost of a roof, yet many companies will squabble over this minute amount. However, it's a surprisingly little-known fact that some washers can play a significant part in corrosion of a roof system and can accelerate deterioration, reducing the life span of the structure if incorrect or substandard washers are installed.

BEWARE OF BLENDS
Washers can be made of many different materials, but few are suited to the rigorous conditions to which they are exposed. As seen in the table on page 79, EPDM, which is a synthetic polymer derived from oil, is the ideal material from which to manufacture washers. Many companies state that they supply EPDM washers; however, because there are no current standards, the percentage of EPDM contained in each washer varies greatly. The number of ingredients in any given EPDM "blend" can range from five to 20 with hugely varying properties, such as UV stability, elasticity, compression performance and resistance to heat aging.

One common washer additive you should be aware of is carbon black. A small amount of carbon black is a necessary additive in EPDM blends because it delivers important performance characteristics at a relatively low cost. These include:

Carbon black's low cost also makes it effective for binding blends with high-clay contents

As rising oil prices drive up the cost of EPDM, some manufactures are increasing the levels of fillers within their blends. These low-EPDM, high-carbon blends almost are impossible to separate visually from a high-quality blend that will have a life span of more than 20 years. A poorly blended formulation can last as little as 18 months before showing signs of breakdown.

CONDUCTIVE CORROSION

It's a surprisingly little-known fact that some washers can play in corrosion of a roof system and can accelerate deterioration, reducing the life span of the structure if incorrect or substandard washer are installed.

Another concern caused by high levels of carbon black is the incidence of bi-metallic corrosion facilitated by the conductive washer. The quantity of carbon, grade of carbon and its dispersion in the blend developed through the washer itself. This occurs when the high levels of carbon black form a conductive chain through the polymer and create an electrolytic cell between two different metals, the screw and the roof. This problem often is misinterpreted as a failure of the fastener or roofing/cladding material. This is an inaccurate and costly assumption.

An indication that the washer is contributing to the corrosion can be small blisters of white rust on the surface of the steel sheet close to the base of the screw head. In severe cases, you will see red rust as the coating is removed and the substrate begins to corrode. In addition, where the corrosion has remained unchecked the structural integrity of the construction envelope will have begun failing.

A SIMPLE TEST

Testing the conductivity of a washer can be done simply by applying a resistance meter to the surface of the washer. Applying a charge of 1,000 volts across the washer and reading the resistance will provide a quick indication of whether the washer is conductive. The true measure of a perfect insulator, which is what a washer should be, is a reading of infinite resistance regardless of the voltage applied.

The degree of conductivity is measured according to the amount of current that will pass through at any given voltage. The relationship between voltage (V), current (I) and resistance (R) is governed by I = V/R. The industry benchmark is that a current flow of less than 0.5 x 10-6 amps is considered acceptable for washers to be deemed nonconductive. This equates to a resistance of no less than 2000M Ohms.

It is advisable to ask for a certificate of compliance from a screw supplier or a similar statement regarding conductivity. You also can perform the test yourself with a simple multimeter.

Recently a major supplier of roofing and cladding material in Australasia made the recommendation that all roofing and cladding must be installed with fully nonconductive washers. This conclusion was reached after extensive external real-world testing was carried out that revealed washers with even the slightest conductivity showed an increase in electrolysis compared with fasteners with nonconductive washers. This recommendation is to be adopted as part of the company's overall roof material warranty this year.

Quality washers are engineered to suit the fastener, roofing and cladding profiles and materials, as well as the final application. The old terminology of "one size fits all" creates false assumption and can lead to leakages caused by poor design.

When looking for a quality washer always ask your fastener supplier the following questions:

By asking these simple questions, you can be assured that your next metal roofing or cladding project will not fail because of the washers.