Composite metal deck is about as forgiving a building product as you’ll find on a site — right up until it isn’t. Most of the problems we hear about after the fact don’t come from a bad batch of steel. They come from a handful of habits that are easy to let slide when everyone’s trying to keep to schedule. Here’s what actually goes wrong, roughly in the order we tend to hear about it.

1. Losing the Chalk Line

Deck sheets are laid rib to rib, and the alignment only stays straight if someone is regularly re-checking it against a chalk line — not eyeballing it against the sheet before. Skip that step for a run of twenty or thirty sheets and the ribs drift out of line just enough to leave gaps at the laps. On a roof, that’s untidy. On a floor deck, before the concrete goes in, those gaps are exactly where wet concrete finds its way through.

2. Not Enough Bearing on the Support

Deck sheets need a minimum bearing length on the beam or wall they’re resting on — as a rule of thumb, at least 38mm (1½”), though the exact figure should come from your structural drawings. Trim a sheet short to make it “fit” and you’ve quietly created a spot with less bearing than the design assumed, which usually means it needs extra fastening — and an inspection — before anyone pours concrete over it.

3. Skipping Temporary Propping When the Deck Actually Needs It

Metal deck is often strong enough to act as its own working platform during construction, carrying the crew and the wet concrete without anything extra underneath. “Often” is the key word — on longer spans, or with certain profiles, the deck needs temporary propping until the concrete has cured enough to help carry its own weight. Whether propping is required isn’t a site decision; it’s on the design drawings, and skipping it because “the last job didn’t need it” is how decks end up permanently deflected.

4. Swapping the Fastener Without Asking

The side-lap screws, or the button-punching pattern, holding sheets together aren’t just there to stop rattling — they’re part of how the deck braces the structure and resists wind uplift. If the specified fastener runs out on site and someone reaches for “something similar” from another box, that substitution should go through the designer first, not get decided on the spot. It’s a five-minute phone call against a structural question nobody wants to answer later.

5. Pouring Concrete the Wrong Way

How concrete goes onto the deck matters almost as much as how much of it there is. Dropping it from height, or dumping it all in one spot before spreading, can dent the sheet or force the side laps open before the concrete has any strength to resist it. The safer habit is pouring low and steady, working across the bay so the load builds up evenly rather than in one heavy patch.

None of these five are complicated to avoid. They just take someone on site treating the deck as a structural element under construction, not as a finished platform waiting for concrete. A quick walk-through before the pour — checking the laps, the bearing, the propping, and the fasteners — catches almost all of it.