Working with aluminium rivets on outdoor projects

Why aluminium rivets earn their place outdoors

If you have ever tried to bolt a gutter bracket back onto a fascia in the rain, you already know why rivets are so useful. Aluminium blind rivets are light, quick to fit from one side of the work, and they resist the weather far better than bare steel fixings. That last point matters in the UK, where a fixing can spend nine months of the year damp and the other three being rained on.

Aluminium also forms its own protective oxide layer, so a rivet doesn't flare up with rust the way a mild steel screw does. You can leave an aluminium rivet in a shed panel, a downpipe joint or a car's inner wing and forget about it. The trade-off is strength: aluminium rivets are not as strong as steel or stainless, so treat them as a fixing for sheet metal, trim and light brackets rather than anything structural.

One thing to watch is dissimilar metals. Putting an aluminium rivet into a galvanised or stainless steel frame creates a small electrical couple, and in wet conditions the aluminium becomes the sacrificial part. A dab of anti-corrosion jointing compound or a thin plastic isolating washer between the two metals will keep the joint sound for years.

Choosing the right rivet and tool

Most DIY and workshop jobs use standard blind (pop) rivets in three diameters: 3.2mm, 4.0mm and 4.8mm. As a rough guide, 3.2mm suits thin sheet and trim, 4.0mm is the general-purpose size, and 4.8mm handles brackets and heavier overlaps.

• Grip range is the thickness of material the rivet can clamp. Every rivet has a minimum and maximum, and if you are outside it the rivet either won't set or will sit loose. Measure your total thickness and pick accordingly.
• Mandrel material matters. Aluminium rivets are often supplied with a steel mandrel for extra setting strength, but the snapped stem stays inside the rivet body. For marine or constantly wet locations, choose a sealed or all-aluminium rivet.
• Large-flange rivets spread the load over a wider area and are excellent for soft or thin aluminium sheet that would otherwise pull through.
• The gun should match the rivet size. A cheap lever gun handles 3.2mm and 4.0mm fine; 4.8mm and above are much easier with a lazy-tong or long-arm tool.

Drilling and preparing the joint

Good riveting is mostly good preparation. Clamp the parts together first, then drill through both layers in one pass so the holes line up exactly. Use a sharp bit at the correct size — for a 4.8mm rivet, a 4.8mm or 4.9mm bit is right. An oversized hole is the most common cause of a rivet that spins or fails to grip.

Deburr both sides of the hole with a larger bit twisted by hand or a deburring tool. Swarf left between the sheets stops them closing up tight, and on outdoor work that gap becomes a water trap.

Spacing follows a simple rule of thumb: keep rivets at least two diameters from any edge and about four diameters apart along the seam. So for 4.0mm rivets, stay 8mm in from the edge and set them roughly 16mm apart. Closer than that and you risk tearing the sheet between holes.

If the joint needs to be watertight, run a bead of sealant or butyl tape between the layers before you close them up. The rivet holds the parts together; the sealant does the weatherproofing.

Setting rivets cleanly

Push the rivet into the hole until the flange sits flat against the work, then squeeze the tool steadily. You will feel the mandrel draw the parts together, then a firm snap as the stem breaks at its designed load. Don't pump the handles in short jabs; one smooth compression gives a much neater set.

• Hold the gun square to the surface so the flange seats evenly.
• Support the back of thin sheet with a block or your hand, or the panel will distort as the rivet pulls.
• Catch the spent mandrels — they fly off with surprising speed and are a nuisance in grass or gravel.
• Check the set rivet: the flange should be tight against the surface and the body firm in the hole with no wobble.

Typical outdoor repairs

Gutters and downpipes: rivet replacement brackets to the gutter, and join downpipe sections with two or three 4.0mm rivets, sealed with silicone. Drill from the outside so the flange faces the weather.

Sheds and outbuildings: overlap joints in aluminium or coated steel cladding hold well with 4.8mm rivets. On a steel frame, isolate as described above and use a rivet with a sealing washer.

Automotive trim: wheel arch liners, number plates, heat shield edges and interior panels are classic rivet jobs. For plastic panels, use a wide-flange rivet or a dedicated plastic rivet so the head doesn't crack the material.

Garden and workshop kit: repairing a wheelbarrow tray, reattaching a mower deck guard or patching a metal toolbox are all quick fixes with a handful of 4.0mm rivets.

Faults to look out for

A rivet that spins usually means the hole is too big or the sheets have not closed up. Drill it out with a bit the same size as the rivet head and start again one size up. If the mandrel pulls straight through, your grip range is wrong — the rivet is too long for the material. And if the rivet sits proud, the joint was too thick for that rivet, so step up to a longer one. When you need to remove a rivet, drill the head off carefully with a bit slightly larger than the mandrel hole, then punch the body through.