CHOICES FOR EXTERIOR FASTENERS
All metal fasteners have the potential to corrode. Fasteners used in corrosive environments and materials require higher levels of corrosion resistance. Starborn offers four types of exterior fasteners (listed in order of increasing corrosion resistance): epoxy coated steel, epoxy coated grade 410 stainless steel, grade 305 stainless steel, grade 316 stainless steel. For applications exposed to salt air, near large bodies of water, swimming pools or other areas where corrosion is more likely to occur, always use grade 316 stainless. Choose the best fastener based on the material being fastened and the environmental conditions of the project location.
1. Epoxy Coated Steel
Starborn epoxy coated carbon steel screws have two levels of protection against corrosion: zinc plating and an epoxy based polymer resin overcoat. The epoxy coating not only provides excellent corrosion resistance, but is designed to adhere to the screw, even after insertion into wood and synthetic decking products ‐ a critical factor in the real world effectiveness of any protective coating.
2. Epoxy Coated Grade 410 Stainless Steel
Starborn epoxy coated grade 410 stainless steel carbon steel screws are hardened so that they can penetrate through steel and aluminum joists while still providing a high level of corrosion resistance. Like other Starborn epoxy coated screws, these screws are zinc plated and have an epoxy based polymer resin overcoat.
3. Grade 305 Stainless Steel
Grade 305 stainless is the most common grade of stainless steel used in exterior fasteners (along with grade 304, which is very similar). Grade 305 stainless fasteners are used in applications where epoxy coated steel does not provide sufficient corrosion resistance. Note that stainless screws are softer than carbon steel, and depending on density of the material being fastened, pre‐drilling may be necessary.
4. Grade 316 Stainless Steel
Grade 316 stainless, sometimes referred to as marine grade stainless, provides the highest level of corrosion resistance. See note about pre‐drilling above.
MATERIAL BEING FASTENED
1. Treated Lumber
In normal environments, Starborn epoxy coated carbon steel screws provide excellent corrosion resistance in treated lumber.
2. Naturally Rot Resistant Deck Lumber
Many tropical hardwoods, as well as cedar, redwood and other woods, contain large amounts of tannins and other chemical compounds that provide natural protection against deterioration. These natural chemicals can also cause staining and corrosion when they come into contact with zinc or carbon steel. For these wood decking materials, stainless steel is always recommended.
3. Plastic and Wood/Plastic Composite Decking
Always follow installation instructions and fastener recommendations provided by decking manufacturers to determine whether stainless steel screws are required or if epoxy coated steel screws are sufficient.
Environmental conditions must be considered separately from the material being fastened. For instance, a treated lumber deck can normally be fastened with epoxy coated steel, but a treated lumber deck next to a swimming pool should be fastened with grade 316 stainless. In general, installations near bodies of water require grade 316 stainless. Applications near salt water and swimming pools are especially subject to accelerated corrosion. In these environments, even with the use of stainless steel, some staining or corrosion is still possible depending on a number of variables:
1. Repeated cycles of condensation and evaporation can cause increasingly high concentrations of corrosive chemicals to accumulate on the fastener. For instance, chlorine based chemicals in swimming pools are very volatile and can be transferred through the air to nearby decks. (Careful chlorination control may minimize this possibility). The condensation and evaporation of salt air will have a similar effect.
2. In addition to condensation, decks located within the ‘splash zone,’ where intermittent splashing from swimmers or occasional waves results in direct exposure of the fastener to salt water or chlorinated pool water, can also cause a buildup of corrosive elements on deck fasteners.
3. Exposure to certain types of chemicals, including some chemicals found in maintenance and cleaning products, can also cause stainless steel to corrode. These include de‐icers, bleach and hydrochloric acid (present in many commercially available toilet bowl cleaners, which are sometimes used for general cleaning purposes).
For decks subject to condensation and evaporation of air containing corrosive elements or located within the ‘splash zone’ of waves and swimming pools, washing with fresh water is a good practice. Some discoloration and staining of stainless steel screw heads occasionally occurs in many marine and pool environments. This discoloration is often present only on the surface of the fastener and may not indicate a problem with the performance and integrity of the fastener itself.