If you’re looking for screws to use with pressure treated wood (which is commonly used outside) and other outside/ coastal/high moisture areas, stainless steel is one of the best screws available. Very importantly, pressure treated wood is protected by chemicals that prevent decay, mold, and bugs, but those same chemicals can cause certain types of screws (plain steel, for example) to have an accelerated corrosion rate (or rust quickly). Selecting the correct type of screws is a major consideration, as it impacts the strength and integrity of the connection, safety, appearance and durability of the connection.
Stainless steel screws provide excellent corrosion resistance and durability for outdoor wooden structures like decks, fences, docks, pergolas, garden beds, and outdoor stairways, among others. Keep in mind that not all stainless steel screws are made the same; when you are building an outdoor wooden structure you must choose the right grade of stainless steel based on the lumber’s chemical treatments, the environmental conditions in which they will be used (e.g., exposure to salt or chemicals), the structure they are used to create, and the cost of the materials.
Why Pressure Treated Wood Needs the Right Screws?
Chemical means are used to apply Wood Pressure Treatments to wood to give it protection against insect infestation and moisture, by penetrating chemicals into the wood fibres. Examples of current treated wood are treated with copper-based preservatives (ACQ, CA, MCA) that are preservative for wood against moisture, but the chemicals will wire other metals with which they come into contact. This creates a corrosion process on these metals.
Using standard carbon steel or drywall screws (or even poor quality plated) into treated timber can cause rusting and discoloration to the timber, as well as increase the potential of failure structurally over time. The risk of failure is even greater with regard to using screws in load-bearing applications (decks, stairs, railings, and elevated surfaces).
Because a stainless screw has a protective passive layer (chromium oxide) on its surface, it is considered to have excellent performance attributes. The passive layer exhibits considerable resistance to rust and corrosion when exposed to freshwater, wood treatment chemicals and harsh conditions in the outdoors.
Are Stainless Steel Screws Good for Pressure Treated Lumber?
Overall, stainless-steel fasteners are good for use with pressure-treated lumber; however, they are often regarded as being the optimal choice for fasteners that will be continually subjected to significant corrosion.
Stainless steel wood screws are common in many forms of exterior woodwork, including decks, marine construction, outdoor furniture, landscaping jobs, and high-end architectural work. Generally speaking, stainless steel fasteners have a longer life expectancy than standard zinc-plated screws and will reduce the likelihood of rust stains around the screw heads.
All users of preserved lumber, contractors, DIY builders, and end-users, want to know if they can use stainless steel screws in preserved lumber; however, their primary concern is determining the appropriate grade and design of screw to suit their application.
304 vs 316 Stainless Steel Screws: Which Is Better for Treated Wood?
S305 and S306 Type Stainless Steel – These types of bolts and screws made from stainless steel can be used with pressure treated wood, however they are both durable but can not be interchanged.
304 Stainless Steel Screws
304 stainless steel screws are often used in general applications of outdoor connections to wood due to their almost complete corrosion resistance, from background use through use to create fences, canopies, planters, etc and for use with trimming at homes’ outer edges.
304 stainless steel fasteners are typically a good value choice when your project doesn’t face exposure to saltwater, heavy industrial pollution, pool chemicals, or extended periods of water. You will generally find these types of fasteners available for sale in most stores and their lifespan will exceed that of regular steel screws & basic plated fastener.
316 Stainless Steel Screws
316 stainless steel screws have a higher resistance to corrosion by chlorides because of the addition of molybdenum to the alloy. Therefore, 316 stainless steel screws are more suitable than 304 stainless steel screws for use in coastal areas, sea related applications, marine structures, walkways, piers, swimming pool decks and all other places that are treated with de-icing salts and/or washed down with chemicals.
In this example project of PT lumber located close to oceans, lakes, swimming pools or moisture-laden areas moisture will break down regular metal fasteners (i.e., nails and screws) due to the high humidity and the water being present in these areas. Therefore, using 316 stainless steel screws would be the preferred method rather than using 304 stainless steel screws. Although purchasing 316 stainless steel screws will cost more than 304 stainless steel screws (because 316 are of a higher grade and price), this cost difference can save you money over many years due to long-lasting constructions of your fastened assemblies with these screws.
When Should You Choose Stainless Steel Screws Over Galvanized Screws?
Many builders will fasten pressure treated wood with galvanized screws (hot dipped), which can be suitable if their specification meets the demands of the project, but with a better looking product and more resistance to corrosion over time, as well as much better long-term performance in extreme exposure conditions, stainless steel screws are usually preferable.
If you need durable materials, refer to these guidelines to select the appropriate stainless steel screw for your project: visible fasteners that have minimal staining, severe weather (rain/humidity), wood treated with copper, etc., and locations with heavy use of coastal/harmful chemical products.
Galvanized screws can be used in more affordable outdoor jobs, but it is necessary to know the quality of the galvanizing. Electro-galvanized screws, which are made using a process that involves electrolysis, are usually too thin to be used with treated lumber because they can wear off or rust quickly.
Best Applications for Stainless Steel Wood Screws in Treated Lumber
Wood screws constructed from stainless steel may be appropriate for various applications where treated lumber is used. Because they are strong enough to hold up against the impacts of changing moisture levels, as well as having a long lifespan, these types of wood screws can serve well in many different types of applications. Examples of where you would typically use wood screws made of stainless steel include constructing decks and fences, building outdoor stairways and railings, creating retaining structures (such as retaining walls), creating planter boxes, building boardwalks, constructing docks, creating patio furniture, and making any other type of landscape lumber.
When visible screws are needed, stainless steel should be used as fasteners because of their durability and corrosion resistance. The appearance of a well-built and finished building may be diminished by rust staining from water sitting around the head of the screw, giving it the appearance of being old and/or poorly maintained. The use of stainless steel fasteners will also help maintain a professional-looking project longer.
How to Choose the Right Stainless Steel Screws for Pressure Treated Wood
Think about all the factors involved when purchasing screws – material, thread form/design, type/style of head, type/style of drive, length and diameter. The way in which the screw is made will also play a part in how well the screw performs.
Using large screw threads when fastening treated wood gives the screw much better holding power as compared to a small screw because they can bite into the timber fibres much better than smaller screws can. A finely sharpened point helps get the screw into the wood or other material quickly, whereas a properly shaped head helps to keep the fibre from splitting out as the screw is being installed, as well as providing additional clamping force on the materials being joined together. Both trim-head and bugle-head screws can be used as decking screws based on what type of finish you want and how you plan to install them.
When fastening down the screw, choose a long enough screw so that it will hold securely, but do not let the screw exceed its specified tolerance of 1” from the opposite face of the screw for normal usage with deck boards, 4” to 5” depending on the thickness of the wood and framing conditions. For structural heavier connection installations always refer to the local building code, engineering and/or manufacturer specifications.
Installation Tips to Improve Performance
Even the finest quality Stainless Steel fasteners do not function properly when installed incorrectly. Stainless Steel fasteners may have better corrosion resistance than many materials, but they are much softer than most high strength [hardened] carbon steel fasteners of similar size and shape. To prevent stripping of the head (screws) and breaking the screw, use the correct screwdriver, drill bit, or driver bit with a fastener at the correct installation speed.
Before you install your new hardwood furniture use larger diameter wood screws.Pre-drilling holes near the end of boards may help reduce the chance of splitting wood when screwing through them, and this will also ensure that screw installation looks nicer than if no pre-drilling were done. Avoid driving fasteners into a wood substrate more than once. If you overdrive fasteners into wood, you will damage the fibre structure of the wood and create voids where moisture can accumulate.
Incompatible metals should not be combined. If stainless steel screws are used in brackets or connectors made from non-stainless steel, there is a chance for galvanic corrosion to occur in wet conditions. When constructing joist hangers, brackets and bolts with treated lumber, use wood-compatible products.
Common Mistakes to Avoid
The most common mistakes made when using screws (screws for use within a building), drywall screws (screws used to install drywall) and cheap galvanized fasteners on pressure-treated wood is that fasteners were not designed to be used with exterior structural timber products. The use of internal screws on wooden products that were designed for the outdoors will result in the fasteners corroding before their expected lifespan.
Another potential issue of the manufacture of the screws in question is the fact that some screws deemed “corrosion-resistant” may not perform adequately when used with treated lumber. Screws which are coated via a process that was designed only for mild exposure will suffer corrosion from the copper-based wood treatment preservatives that most types of wood are treated with. Always verify prior to using any corrosion-resistant screws that the screws you wish to use are specifically rated to be used with treated lumber.
Choosing 304 SS in an area where 316 would be appropriate is 1/3 of the wrong decision; you will have a lower initial cost on 304 SS, but run the risk of premature corrosion. However; this is not an acceptable risk due to exposure to salty, coastal, or chloride – laden environments.
Do Stainless Steel Screws React With Pressure Treated Wood?
Stainless steel has been shown to interact chemically with copper based preservatives at a significantly slower rate than non-stainless steel products, providing a safe combination of stainless steel with treated lumber. As such, many builders, architects, and fastener suppliers support the use of stainless steel for creating wood structures or buildings that require superior quality and durability in the outdoors.
Conversely, compatibility will vary based on the entire assembly. If you use a stainless steel screw (or fastener) with any other dissimilar material (such as a steel washer, bracket or connection point) will also have durability issues unless all other parts of the system are either treated for compatibility with treated lumber or protected from the elements. The ability of any fastener system to perform properly is only as strong as its weakest component(s).
Are Stainless Steel Screws Worth the Extra Cost?
When it comes to outdoor construction projects, usually, stainless steel screws are best suited to use – typically more expensive than their coated or galvanized counterparts, but far less time and effort will be needed towards continual upkeep (such as eliminating rust stains) of the finished product; and also add to its longevity. If your project is either large, visible, difficult to repair, or exposed to moisture; it would make sense financially to consider adding stainless steel screws.
The environment and performance requirements of a project will dictate the proper fasteners for larger applications, but in general, you should choose stainless steel fasteners when there would be a large cost associated with failure (i.e. safety, inconvenience). For example, backyard fences don’t need the same quality fasteners as coastal decks or boat docks.
FAQs
Are stainless steel screws ok for treated lumber?
Stainless steel screws can safely be used in conjunction with treated timber because they are resistant to corrosion caused by both the water and chemicals used to preserve the wood. For most outdoor uses 304 stainless steel will work perfectly; however, when the screws will be exposed to a coastal environment, ocean water, or highly chlorinated (swimming pool) environments, you should use 316 stainless steel screws.
What type of screws should I use in pressure treated wood?
Your choice of fastening system for the installation of pressure treated wood should depend on the type of fastener utilized. It is recommended that you use a stainless steel fastener as your first choice for fastening the wood. Other options include ‘hot-dipped galvanized’ screws intended for use with either application type, although they should not be confused with zinc-plated fasteners, which are generally used for indoor applications only.
Can I use 304 stainless steel screws in pressure treated wood?
Of course, you can use 304 stainless steel screws for pressure-treated wood in many outdoor applications. Outdoor applications utilizing 304 stainless steel screws can include decks, fencing, porch coverings, garden structures, and general exterior timber (in areas not adjacent to an ocean). However, if your project will experience contact with saltwater or pool chemicals, you should consider using 316 stainless steel screws instead of 304 stainless steel screws.
When should I use 316 stainless steel screws?
316 stainless steel screws are the best choice for projects near saltwater exposure, during shower installations, in areas of high moisture, and where chemical exposure may occur. Because 316 stainless steel offers superior resistance to chloride-related corrosion than 304 stainless steel, using it on your project is an excellent idea.
Will stainless steel screws rust outdoors?
Although stainless steel does not rust very easily, it can corrode when placed under certain conditions. Because of this, use high-quality stainless steel screws as much as possible when doing typical outdoor work. Nonetheless, when using screws in a marine environment (or for chemicals), you may want to consider using 316 stainless instead of 304 because the extra corrosion resistance would give you more confidence for a long-lasting result.
Can stainless steel screws be used for decking?
If you’re choosing a decking material made of pressure treated wood, cedar, red cedar or any other type of hardwood, there really isn’t a better alternative than a stainless steel screw as a fastener to complete the look of your deck. Stainless steel screws help prevent the rust and stain on your deck as well as give a very clean finish. If you are planning on building a deck along the coastline or near water like the ocean, we suggest that you utilize 316 grade stainless steel deck screws.
Whenever you are using pressure treated wood for an outdoor project or a project that needs to last for a long time, you will want to use stainless steel screws. For use on most outdoor wood projects, you should use 304 stainless steel screws. For coastal or marine environments, poolside, or chemical exposure, you will want to use 316 stainless steel screws. Avoid using drywall, ordinary steel, and low-quality plated screws as they will corrode quickly in these circumstances and failure of the structure will result.
