How do I check my deck's screws, hangers and hardware for rust, and when is it a problem?
Short answer
Once a year, get under the deck with a flashlight and look at every joist hanger, post base, bolt and screw head. Light, even surface rust on galvanized hardware is cosmetic. Flaking, pitting, rust streaks running down the wood, white powdery corrosion or a hanger that has lost its coating is a problem, and so is any screw head that has rusted through or snapped. Near the coast, hardware often fails before the wood does, so this check matters as much as probing for rot.
Where to look
Start on top. Walk the deck and look at the screw heads. Any that stand above the surface, have black rust rings around them or have lost their heads need attention. Then look at the railing: the bolts through the posts, the brackets at the rail, and the screws in the balusters.
Underneath is where the structure is. With a flashlight, look at each joist hanger and its nails, the hangers at the ledger, the post bases where posts meet concrete, the bolts through the beam and posts, and the lag screws or through-bolts that hold the ledger to the house. On stairs, check the stringer hangers and the bolts at the landing.
- Deck screw heads and hidden fastener clips.
- Railing post bolts and rail brackets.
- Joist hangers and hanger nails, especially at the ledger.
- Post bases and anchor bolts at concrete.
- Beam-to-post connectors and bolts.
- Ledger bolts and the flashing above them.
Reading the rust
Galvanized hardware is steel with a zinc coating that sacrifices itself to protect the steel. A dull gray or lightly rusted surface means the zinc is doing its job. Orange rust that is flaking, pitting that you can feel with a fingernail, or a hanger that has gone uniformly brown means the zinc is gone and the steel itself is corroding. White, powdery deposits are the zinc corroding fast, which is common near the ocean and on treated lumber.
Rust streaks running down the wood below a connector are a sign the hardware has been actively corroding for a while. A screw head that snaps when you try to tighten it, or a hanger nail that has rusted to a thread, is past cosmetic. Structural connectors in that condition should be replaced before the deck is used heavily.
Why coastal hardware fails faster
Salt air is half the story. The other half is the lumber itself. Modern pressure-treated wood uses copper-based preservatives that are more corrosive to steel than the older treatments were. A bright zinc-plated screw or a light-gauge hanger that would last decades inland in untreated wood can fail in a few years in treated lumber a mile from the beach.
Mixing metals makes it worse. A stainless bolt in a galvanized hanger, or an aluminum rail bracket screwed to a steel post, sets up a small battery that eats the less noble metal. Keep each connection all one metal.
Deck screws and boards
On wood decks, a screw head that has lifted is usually the board moving, not the screw failing, and driving it back down is fine. A screw that spins without biting has lost its wood, and the fix is a slightly longer or thicker screw, or filling the hole. Black streaks spreading from screw heads on cedar or redwood are tannin reacting with a non-stainless screw and are a cosmetic warning that the screws are not rated for that wood.
On composite decks with hidden fasteners, lift a board at the edge if you can and look at the clips. Corroded clips let boards lift and squeak. Stainless clips are the norm on coastal work for exactly this reason.
What to do about what you find
Cosmetic rust: note it, rinse the hardware with fresh water a few times a season, and check it again next year. Flaking or pitting on a connector: replace it, matching or upgrading the rating, which near the coast means stainless or heavy hot-dip galvanized hardware made for treated lumber. Replacing a hanger or a post base means temporarily supporting that part of the deck, so it is a job for a builder.
If several connectors have failed, or the deck has started to sag, bounce or pull away from the house, stop using it until it has been looked at. A ledger connection is a structural question, and where there is any doubt, a licensed structural engineer should weigh in.
What the code expects
As consumer information: the model building codes used in California require fasteners and connectors in contact with preservative-treated lumber to be hot-dip galvanized, stainless steel, or otherwise rated for that use, because of the corrosion issue described above. If your deck was built with the wrong hardware, that is worth knowing before a small repair turns into a larger one. The current adopted codes are published by the ICC and the California Building Standards Commission.
Related questions
Can I just spray rusted hangers with rust-inhibiting paint?
Paint over light surface rust slows it down and is fine for cosmetic cases. It does nothing for a hanger that is flaking or pitted; the steel has already lost thickness, and paint will not restore its strength. Replace those.
How do I know if my hardware is stainless or galvanized?
A magnet is a quick test: most stainless deck hardware is weakly or not at all magnetic, while galvanized steel grabs the magnet hard. Stainless stays bright or picks up light tea-colored staining; galvanized goes dull gray and then rusts orange when the coating is gone.
Sources and further reading
- ICC International Residential Code (Fasteners, Section R317.3) (codes.iccsafe.org)
- California Building Standards Commission (www.dgs.ca.gov)