Concealed or hidden deck fasteners can give a great look to deck surfaces. People love them. But concealed fasteners have limitations. Here’s 6 key things you should know before deciding how to fasten your decking.

Hidden Fasteners Make a Beautiful Looking Deck, but…

Hidden fasteners are not as strong as face screws. Screwing deck boards directly through the face of the decking, into your deck joists, is the strongest way to fasten decking. Period.

Face Screws are the Strongest Deck Fasteners

If a strong, long-lasting deck fastener is your goal, stainless steel deck screws work best. If you don’t like the look of screw heads on your decking, there are ‘trim-head’ deck screws. The heads of trim head deck screws are not as visible, and the fastening is quite strong. Especially with hardwood decking boards.

Ceramic-coated screws offer decent rust resistance thanks to a strong exterior coating, but they lack the fully stainless steel composition that produces the best results. While ceramic-coated zinc screws are less rust-resistant, they come at a lower price than stainless steel.

Concealed Fasteners are More Vulnerable to Natural Decking Movement Than Deck Screws

Exterior deck boards are exposed to all sorts of weather extremes. Heat. Rain. Snow. Exposure to direct sunlight. Natural wood decking expands and contracts with moisture content. All the time. Yes, even kiln dried hardwood decking.

Concealed fasteners typically only attach through one edge of a deck board. The other edge of the deck board is free to ‘float’. As wood deck boards dry, they shrink. When wood decking picks up moisture they expand.

Concealed Fasteners Work Best with Narrower, Thicker Deck Boards

Why? When you use a concealed or hidden fastener for your decking, the side with the screw will ‘stay put’. The other side will ‘move” (expand and contract with moisture gain or loss). This changes the width of the gap between your deck boards. Narrower deck boards expand and contract less than wider deck boards. So, the change in the gap between your deck boards is smaller and less noticeable.

Narrower deck boards provide more fastening power per square foot. When you do the math, you’ll notice that you gain about 50% more fastening over your deck. This makes for a stronger deck.

Thicker deck board are stronger than thinner deck boards. They’re tougher. They help stabilize your deck frame and make a better performing overall deck. So, a thicker, narrower deck board is ideal with hidden fasteners. When using concealed deck fasteners, 5/4 x 4 nominal decking and 21 mm x 4 nominal decking sizes perform best.

Where NOT To Use Concealed Fasteners?

There are certain places and conditions where you really shouldn’t even consider using a concealed fastener. Here’s a short list of places to not use concealed or hidden deck fasteners:

• Decks that are closer than 30” above the ground – use face screws.
• Decks with little under-deck ventilation. If your deck is not ventilated on three sides, use face screws
• 1 x 6 decking (nominal) performs best with face screws.
• If the area below your deck does not pitch away from your structure – fix it, then use deck screws
• If the area below deck does not drain properly – fix it, and use deck screws

Choose the Right Fastener That Works Best with Your Decking

We have tested nearly every deck screw, concealed and hidden deck fastener on the market. Some work better than others. Some concealed deck fasteners only work with a specific decking material. For example, many of the composite decking options require a particular fastener.

Some of the ‘bang-in’ style concealed fasteners will split the wood decking, especially hardwood decking. Concealed fasteners for hardwood decking work best with pre-grooved decking. Thermally modified decking is often brittle and should be screwed down for best performance. Softwood decking may be screwed down or attached with a hidden fastener.