Why your deck boards keep popping up

← Back to the journal

You walk across your deck, hear the familiar creak, and there it is again. The same nail that was flush with the board two months ago is now sitting proud, waiting to catch the sole of someone's bare foot. You grab the hammer, give it a couple of taps, and it sinks back down. Problem solved.

Except it isn't. That nail will be back. Maybe not next week, but give it a month or two and it'll be up again, along with a few of its mates. I see this on almost every timber deck I look at in Auckland, and the conversation is always the same: "I keep hammering them down, but they just keep coming back up. What's going on?"

The short answer is that nails were never the right fastener for deck boards in the first place. The longer answer is about how timber moves, why that movement makes nails fail, and what you should be using instead.

What's happening under your feet

Timber isn't static. It swells when it absorbs moisture and shrinks when it dries out. In Auckland, where you get decent rain followed by hot, dry stretches, that cycle happens all year round. Your deck boards are expanding and contracting with every weather change, and every time they do, they're working against the fasteners holding them down.

Nails hold through friction. The shank of the nail grips the wood fibres around it, and as long as those fibres stay tight, the nail stays put. But when the board swells, it pushes the nail up slightly. When it shrinks again, the nail doesn't come back down with it. The fibres around the nail have been compressed and they don't spring back into the same position. Over a few cycles, the nail loses its grip entirely.

This is worse on hardwoods like kwila, which move more than treated pine and are denser to start with. A nailgun-driven steel nail in kwila is on borrowed time from the day it goes in. Give it a year or two of Auckland weather and it'll start popping. Give it five and you'll be hammering them down every couple of months.

Why hammering them back down doesn't work

Every time you hammer a popped nail back into the board, you're making the problem worse. The hole the nail came out of is now slightly larger than it was. The wood fibres around it have been crushed and won't grip as well. You've bought yourself a few weeks at best before that same nail is back up again.

And if you keep doing it, you'll eventually hammer the nail right through the underside of the joist. I've seen decks where half the nails have punched clean through and are just sitting in the board with no purchase at all. At that point, the board is being held down by the nails that haven't failed yet, and you're one strong gust of wind away from having a loose board that could trip someone.

Screws are the answer

Screws hold through thread engagement, not friction. The thread cuts into the timber and locks the fastener in place, and because the screw is actively pulling the board down onto the joist, it doesn't rely on the wood staying exactly the same size. When the board swells and shrinks, the screw moves with it. It doesn't pop.

The job is straightforward. Pull the nail out, drive a decking screw into the same hole. If the hole is so worn out that the screw won't bite, plug it with a wooden toothpick or a small sliver of timber, add a dab of wood glue, let it set for a few minutes, then drive the screw in. The screw will cut its own thread and lock down tight.

You want trim-head decking screws if you're bothered about the look. The head is smaller than a standard screw and sits closer in size to the old nail, so it's less obvious you've made a swap. If you're replacing all the fasteners on a section of deck, you can use standard decking screws and nobody will notice once the deck weathers a bit.

How long does it take?

If you've got an impact driver and a bag of screws, you can replace ten to fifteen popped nails in an hour. Pull the nail with a claw hammer or pry bar, drive the screw in with the driver, move on to the next one. It's not complicated work, but it does need doing properly. If you're replacing fasteners across the whole deck, budget a morning or an afternoon depending on the size.

The screws themselves are cheap. A box of 500 trim-head decking screws is around fifteen dollars at Bunnings or Mitre 10. You'll get through maybe fifty screws on a typical small deck with a dozen popped nails. If you're doing the whole deck, you might use two or three hundred, but you're still looking at under fifty dollars in materials.

When to call someone

If you've got a few popped nails and you're comfortable with a drill, this is a job you can do yourself in an afternoon. If you've got dozens of them, or if you're looking at the deck and realising that half the boards are loose, or if you're just not keen on spending your weekend pulling nails, that's when you call someone.

I charge by the hour for this kind of work. Most small decks with a handful of popped fasteners take an hour or two to sort out properly. I'll check the whole deck while I'm there, replace anything that needs replacing, and make sure the boards are secure. You'll know it's done right and you won't be hammering nails down again in three months.

Stop hammering, start screwing

Popped nails are a symptom of using the wrong fastener for the job. Hammering them back down is a temporary fix that gets less effective every time you do it. Screws hold better, last longer, and don't pop when the timber moves.

If you've got a couple of popped nails, pull them out and replace them with screws. If you've got dozens, either set aside an afternoon to work through them or get someone in to do it properly. Either way, stop hammering. You're wasting your time.