Do I have to use decking screws, or will ordinary screws do?
What a decking screw is actually designed to do that a general screw is not, and the two features that genuinely matter outdoors.
- Difficulty
- beginner
- Time
- 10 min
- Read
- 2 min
Short answer
A decking screw's real advantages are its corrosion coating and its head, which is shaped to pull itself flush into softwood without a countersink. If the screw you have is rated for exterior use and for treated timber, and you countersink it, it will do the job. If it is a bright zinc indoor screw, it will not, whatever it is called.
Decking screws are sold as a distinct product, and much of what separates them is genuine engineering rather than packaging. But the important half of that engineering is corrosion resistance, which is a property you can check on any screw, rather than anything magical about the shape.
Step by step
- Check the coating first, because it is the part that decides the lifespan.Decking sits wet, and modern preservative-treated timber is chemically aggressive to zinc. The screw needs to be stainless or carry a coating specifically rated for treated timber and exterior use.
- Look at the head shape.Most decking screws have a countersunk head with small ribs or nibs under it that cut their own recess as the head arrives, so it finishes flush without a separate countersink operation. On a deck with hundreds of screws that saves real time.
- Look at the thread arrangement.Many have a coarse lower thread and a small reverse or serrated section below the head, which cuts the top board cleanly and stops the fibres bulging up around the head.
- Check whether the type is partially threaded.A deck board has to be pulled down onto the joist. A plain shank near the head does that; a fully threaded screw can hold a slightly bowed board off the joist.
- Use the right drive.Torx is close to universal on decking screws for good reason: you are driving several hundred long screws, often at an angle, into wet timber, and Pozidriv will cam out and round heads long before you finish.
- Substitute honestly if you are using something else.An exterior-rated stainless or coated screw of the right length, partially threaded, countersunk properly, is a perfectly good deck fixing. A bright zinc general-purpose screw is not, and will stain and fail within a couple of seasons.
Tips
- Pilot the ends of boards. Decking is fixed close to board ends more than almost any other job, and that is exactly where softwood splits.
- If the deck is near the sea or a pool, use A4 stainless rather than A2 or a coated steel screw.
- Two screws per joist per board is the normal pattern. One screw lets the board cup and rock.
Common mistakes
- Using galvanised screws in modern treated timber — Current copper-based preservatives corrode zinc coatings, so the fixing loses section, the board loosens and dark staining bleeds out around every head.
- Driving screws hard enough to bury the head — A head crushed below the surface creates a dish that holds water at every fixing point, which is where a deck board starts to rot.