In the Previous Article, we have covered about the significance of Washer for Roofing Projects. In this part we will discuss about the compound interest factors that need to be considered for roofing and DEKS the Leaders in the field Defines the True-Blue EPDM Washers helps to meet the requirements.
Application of Washers with Screws in a roofing project
There are several uses of using washers with screws. The main purpose of course is to prevent damage to the installation material. If the material is soft, tightening of the screw can dig into the material causing surface damage. A washer will distribute the force over a greater area (as already mentioned) resulting in greater force being applied before damaging the surface. Secondly washers with screws helps to prevent pull-through. Pull-though can happen if the material is soft or damaged around the hole. The force of the fastener being tightened may be enough to actually pull it straight through the material (this is often seen on cars when the hole begins to rust). A washer allows the force to distribute creating less focused pressure. Third reason that in washers with screws, the screw can rest on a smooth even surface. If you are screwing into a coarse or uneven surface, the head of the screw may end up feeling tighter than it should or getting stuck. The washer allows for a smooth surface to the screw to slide against as it is installed to make installation easier and more secure.
Because washers are small and relatively inexpensive, their importance in a roofing project is sometimes overlooked. However, a poor quality washer can result in enormous costs if it is badly designed or made of inferior material. Early breakdown of the washers will result in, at best, the replacement of all screws and seals across the entire roof, and at worst, considerable water damage to the building. The washer is vital in maintaining the integrity of the roofing system. Although washers tend to look the same, chemical analysis shows that their performance differs dramatically. Only a premium EPDM compound is suitable for use on metal roofs, particularly if the washer and fastener are powder coated and baked after assembly.
The standards of a quality washer for roofing
- The washer must comply with industry standards and supports the life and integrity of the roofing system.
- The right balance of hardness, tear strength and compression performance determine how well a cut washer assembles, compresses and resists the tearing effects of swarf, and keeps the screw sealed throughout its life on the roof.
- Washer Integrity and Exposure to Heat
- Washers from materials other than EPDM will quickly breakdown on the roof as temperatures climb in the heat of the day. Research shows that on a 23˚C (73˚F) day a metal roof temperature can climb to 85˚C (185˚F).
“It is important to realize that high heat affects tear strength. With 4.5 fasteners per square metre of roofing sheet, washers play a significant role in any roofing project. All black washers are NOT the same – even when they look identical.”
Rubber Sealing washer must simply cover and seal the hole through which the fastener is installed. In practice, however, it must also cover and seal alignment errors, oversized holes, miss-shaped holes, holes left jagged by drill entry or thread tearing, and elongated holes caused by expansion and contraction of the cladding material. The rubber should also continue sealing effectively for the expected life of the roofing material or installation.
Technical Specifications for any suitable rubber formulation for washer
The following are some of the fundamental and generic considerations which need to be recognised for any suitable rubber formulation.
Compression Set for Rubber Sealing washer:
The measure of the resilience of the basic material, to residual deformation after compression or removal of an imposed strain. It demonstrates the ability of a rubber compound to retain elastic properties after prolonged action of compressive stresses. At lower temperatures, it is a measure of the compound’s physical relaxation, while at elevated temperatures it is a measure of the compound’s chemical relaxation. In service, the polymer is repetitively compressed by the expansion and contraction of the structure. During contraction & expansion cycles (day & night, or summer & winter) respectively the polymer must be sufficiently resilient to rebound to its original shape, maintaining a full seal.
Stress Relaxation and Creep of Rubber Sealing washer:
Stress relaxation is a slow-decay, or time-dependent relaxation, of the stress in a polymeric material under constant deformation or compression. It is attributed to a chemical breaking of primary chemical bonds in the molecular chains. Creep is a time-dependent increase in deformation under constant load. It is primarily due to physical molecular chain slippage and thus is characteristic of the viscous flow of the elastomers. Stress relaxation and creep rate are related and are important considerations for the continuing ability of the rubber to seal when under constant load imposed by the installed fastener.
Elongation criteria for Rubber Sealing washer:
The measure of elasticity of the basic material, or the resistance to residual deformation after elongation. During installation by high-speed drills various physical interferences pull and rip at the material.
Tensile Strength of Rubber Sealing washer;
Tensile strength is critical because the spinning motion of the screw during installation can destructively impact low-tensile material when the washer meets the cladding. Seal failure can occur because the elastomer has crumbled or torn during installation.
Environmental Aging condition for Rubber Sealing washer:
Various changes can occur in a rubber component as a result of the conditions under which it is used or stored. If the conditions are too severe the rubber rapidly becomes unserviceable. Aging of elastomers involves a progressive change in their physical and chemical properties, usually marked by deterioration. Under severe conditions, the elastomer may become unserviceable after only a short time. The major factors liable to cause deterioration or degradation of rubbers used in sealing applications are oxidation, the effect of heat, U.V. light and weathering, ozone, chemical attack and the effect of metal ions.
Electrical Properties to consider for Rubber Sealing washer:
The intrinsic electrical and dielectric behaviour of rubber washers has recently become the focus of possible mechanisms for the accelerated corrosion of some roofing material in severely corrosive environments. Recent investigations suggest possibilities that a similar mechanism to corrosion between dissimilar metals can exist between some rubber washer materials and some other roofing materials. Compounding changes to modify fundamentally the electrical and dielectric behaviour of rubber washers can adversely affect all the previously mentioned proportion
‘It is important to realise that high heat affects tear strength. Therefore selecting the correct washer type is pivotal for long shelf life of a roof. ETHYLENE PROPYLENE DIENE MONOMER is perhaps the best option for any roofing project.’
What is EPDM and why it serves as good washer choice?
EPDM became the seal of choice with the leading roof fastener manufacturers. This terpolymer elastomer is particularly well suited for sealing washers due to its resistance to water, chlorinated water, dilute acids, alkaline, ozone and oxidizing chemicals. It has a negligible absorption rate, is not susceptible to swelling, and can withstand temperatures up to 100°C
This thermoset membrane is compound from rubber polymer and is often referred to as rubber roofing. The American Society for Testing and materials (ASTM) classifies this material as an M Class Polymer. Ethylene and propylene derived from oil and natural gas, are organic building blocks of EPDM. When combined with diene to from the basic rubber matrix, the result is long-chain hydrocarbon with a backbone of saturated molecules and pendant double bonds. The Practical translation is ethylene, propylene and diene combine to form a large molecule that is very stable when exposed to sunlight, heat, ozone (UV) and moisture.
The range of employment and durability of EPDM elastomeric seals is as follows:
|Temperature resistance||-40° to 100° C|
|Abrasion resistance||Good to Very Good|
|Residual compression set||Very Good|
|Water resistance||Very Good|
|Acid resistance||Good to Very good|
|Alkali resistance||Very Good|
|Ozone resistance||Good to Very good|
|Weathering resistance||Very Good|
|Animal and vegetable oils||Very Good|
|Ageing in sunlight||Very Good|
|Ageing in heat||Very Good|
|Ultraviolet resistance||Very Good|
|Description||Closed cell EPDM foam, airtight and waterproof. Excellent resistance to ageing, oil, solvent and many chemicals. Highly consistent cell structure and thickness with no voids or inclusion. Ideally suited to stringent automotive tolerances|
|Tensile strength||6kg/cm2 min|
|Hardness||20±5 HS(C type)|
|Compression set||30% max|
|Deflection weight||@25% 400-800 g/cm2|
|Water absorption||5% max|
|Ozone resistance||120 hrs (20% stretch none crack) (50pphm* 38 C)|
|Service temperature||-290 to 1100 (noncombustible)|
|Format||Sheets (3mm to 10mm)|
- DRIVE FASTENER TO CORRECT DEPTH
- Provide visible marker of over-driving
- Reduce likelihood of stripping
- Around shank & head
- Against roof material
- METAL ON METAL ABRASION
- Provide cushion between metal surfaces
- THERMAL CYCLIC LOADING
- Ease of movement for thermal expansion & contraction
EPDM washer Advantage for roofing project
A common belief exists that as long as a roofing fastener has a washer, it will do the job. This, however, is not true. To understand the necessity of identifying and using quality washers and seals, it is important to first understand the function of a washer in a roofing system.
A washer must be able to withstand all the environmental elements it is exposed to. These include UV degradation, salts from marine environments, acid from industrial pollution, rain, extreme heat, fumes and gases from within factories and plants, etc. While exposed to these conditions the washers must remain elastic, intact and watertight for the life span of the complete roofing system. The cost of washers is a fraction of 1% of the cost of a roof, yet many companies will cut corners when selecting washers and opt for a lower price rather than a decent quality washer. It is a surprisingly little known fact that some washers can play a significant part in the corrosion of a roof system and can even accelerate deterioration, reducing the life span of the structure if incorrect or substandard washers are installed.
Beware of blends Washers are made of a variety of materials but few are suited to the harsh conditions to which they are exposed. EPDM – a synthetic polymer derived from oil – is the ideal material from which to manufacture washers. Many companies state that they supply EPDM washers, but because there are currently no standards in place that specify the percentage of EPDM required in the washers, the EPDM contents vary greatly. The number of ingredients in any given EPDM blend can range from 5 to 20 with hugely varying properties, such as UV stability, elasticity, compression resistance and resistance to heat ageing. An important washer additive is carbon black. A small amount of carbon black is required in the EPDM blend as it offers important performance characteristics at a relatively low cost.
These characteristics include:
- High UV resistance
- Improved elasticity
- Weathering resistance
- Assistance with manufacturing methods
The low cost of carbon black makes it effective for binding blends with high clay contents. As rising oil prices lead to an increased price of EPDM, some manufacturers increase the level of fillers in their blends in order to keep costs down. These low EPDM, high carbon blends are almost impossible to distinguish visually from high quality blends that have a life span in excess of 20 years. A poorly blended formulation can last as little as 18 months before showing signs of deterioration.
EPDM elastomers are uniquely suited for many sealing applications due to their outstanding ozone resistance and weather ability, good heat resistance, low-temperature flexibility, low compression set, and resistance to chemical attack. Furthermore, they exhibit very good electrical insulation properties, good low-temperature properties, and resistance to heat and steam. Economic incentives for using these polymers have also been realized because of its favourable specific gravity and ability for easy incorporation of fillers and plasticizers and yet show favourable tensile and other property responses. EPDM also exhibit excellent compatibility to many inorganic and polar organic fluids but have limited resistance to aromatic hydrocarbons. Properly formulated ethylene-propylene rubber (EP) displays many important properties otherwise available only at a premium cost.
When looking for a quality washer, always ask your fastener supplier the following questions:
- Does the washer have a warranty?
- Is the washer quality traceable (who made it)?
- Is the technical data and support available to be viewed?
- Has the washer been manufactured to suit the fastener and application that I am using it for?
- How can I tell I am getting what I am paying for?
By asking these simple questions, you can be assured that your next metal roofing project will not fail because of the washers.
The fundamental and generic considerations need to be recognized for any suitable rubber formulation. Formulation with a low level of carbon black is the way to go. Negligible electrical conductivity is also an important criterion. True Blue EPDM Washer of DEKS Industries compatibility meets all necessities required. DEKS EPDM Washers exhibit exceptional performance and provide compatibility with All metal Colour Coated ROOFING Sheets.
The EPDM seal can be inseparably bonded to washers of galvanized carbon steel, aluminium or stainless steel, or loose. Both provide a leak free and long-lasting seal. Leading Consultants recommend the use of EPDM sealing washers with low in carbon black. Adaptability feature allows it to be applied to virtually any roof surface: Flat, Spherical, Curved or slanted.
Article contributed by Industry expert