A squeaky outdoor bench is usually caused by loose hardware or two surfaces rubbing together under weight. The fix is almost always simple: tighten everything, lubricate the right spots, and create a little separation where wood and metal meet.
Start by finding exactly where the squeak is coming from. If you can, ask someone to sit on the bench and slowly shift their weight while you listen near the armrests, backrest, legs, and seat slats. If you are on your own, sit down and rock side to side. The noise will usually point you to one or two joints.
Step 1: Tighten all fasteners. Over time, bolts, nuts, and screws work themselves loose as the bench flexes. Grab a wrench, socket set, and screwdriver, then go over the entire bench. Snug up every fastener you can see. Do not crank them down hard enough to split the wood, but remove any obvious play. If a screw spins in place and will not tighten, the hole may be stripped. Pull the screw out, fill the hole with a wooden toothpick or matchstick dipped in exterior wood glue, let it dry, then drive the screw back in. For larger stripped holes, switch to a slightly thicker stainless steel screw.
Step 2: Lubricate the joints. Squeaks happen when metal rubs on metal or wood rubs on metal. A dry lubricant or silicone spray works best for outdoor benches because it does not leave a sticky film that collects dust. Spray the contact points where the seat slats meet the frame, where the backrest attaches, and where the legs connect to the supports. Wipe away any excess. For metal-to-metal pivots, white lithium grease is a longer-lasting option. For wood-on-wood friction, rub the joint with paraffin wax, a plain candle, or powdered graphite. Avoid cooking oil and WD-40 as a long-term fix because they can become gummy or wash away after a few rains.
Step 3: Add rubber or nylon washers. If the bench still creaks after tightening and lubricating, separate the rubbing surfaces with a thin barrier. Place rubber or nylon washers between metal brackets and wood slats, or between metal parts that touch. These are easy to find at any hardware store. This works especially well on benches where a wooden seat sits directly on a metal frame. The washer absorbs the tiny movements that cause the noise.
Step 4: Repair loose or cracked wood. Small cracks in a wooden joint can open and close when someone sits down, and that produces a creaking sound. Force exterior wood glue into the crack with a toothpick or small brush, clamp the joint until the glue dries, and wipe off any squeeze-out. If a mortise-and-tenon joint has become loose, tap a thin wooden shim or wedge into the gap before re-securing the joint.
Step 5: Protect the bench from moisture. Wood swells when it gets wet and shrinks as it dries. That cycle loosens joints and creates the conditions for squeaks to return. Once your bench is quiet, keep it that way by touching up any worn paint, stain, or weatherproofing sealer. Check the hardware at the start of each season and tighten anything that has worked itself loose.
That usually solves it. In most cases, the first two steps, tightening and lubricating, will stop an outdoor bench from squeaking before you even need to reach for washers or glue.