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Drain Holes and Sealed Tubing in Gate Frames

By leander metal gates hub

A hollow gate frame will hold water unless the builder gives that water a way out or keeps it from getting in. Rectangular and round tubing is the backbone of most modern gates, and a tube that looks sound from the outside can rust from the inside for years before anything shows. A small drain hole at the right spot, or a properly sealed end, makes the difference between a frame that lasts decades and one that fails quietly from within.

The problem is easy to overlook because it cannot be seen. Paint covers the outside of a tube, but the inside surface is bare or lightly coated, and any water that enters it stays. This article explains how water gets in, why it matters and the details that deal with it.

How water enters a hollow frame

Water finds its way into tubing through more openings than most owners realize.

• Open tube ends left uncapped after cutting.
• Gaps at weld joints where the weld does not fully seal the seam.
• Holes drilled for hardware, hinges, latches or decorative fittings.
• Pinholes caused by incomplete welds or corrosion that started on the outside.
• Condensation, where warm humid air enters a tube and cools at night, depositing droplets on the inner wall.

Condensation deserves special mention. A sealed tube is not necessarily dry inside. Temperature swings between hot afternoons and cooler nights cause the air within a tube to expand and contract, pulling in moist air through tiny gaps and leaving moisture behind as it cools. Over thousands of cycles, a tube with even a small leak accumulates water.

Why it matters

Water sitting at the low point of a tube corrodes the wall from the inside. Because the tube is hollow, the damage is hidden. The wall thins gradually, and the first visible sign may be a rust stain weeping from a joint, a bulge in the paint or a rail that suddenly bends under normal load. By that time, much of the wall at the lowest point may be gone.

The lowest sections are most at risk. Vertical pickets collect water at their bottoms, the bottom rail gathers water along its length wherever it sags, and the lower ends of posts, where they meet concrete, may stand in water inside as well as outside. Freezing, though uncommon in Leander, adds a second danger, as ice expands and can split a water-filled tube.

The two strategies: seal or drain

There are two sound approaches, and a good gate uses one of them consistently.

The first is to seal each section completely. Welded end caps, fully welded seams and no unplugged holes keep water out. Sealing works best when it is thorough, because a single pinhole lets in moisture that can never escape. For this reason, some fabricators go further and fill sealed sections with a rust-inhibiting material or purge them with dry air before sealing.

The second is to drain each section. A small hole, often one quarter to three eighths of an inch, drilled at the lowest point of the tube lets water run out. Vertical members get a hole just above the bottom cap or at the very end. Horizontal members get a hole on the underside, placed at the lowest point of the span when the gate is hung. The hole must be on the gate's actual low side, taking account of how the leaf sits, and not just where it lay on the shop bench.

A mixed approach causes trouble. A tube that is mostly sealed but has one unnoticed leak and no drain fills slowly with water. A tube with a drain but also an open top lets rain run straight through, which is acceptable only if the drain can handle it and the interior is protected.

Details that help

Careful builders add several small features.

Drain holes should be burr-free and located so they do not leave a stain on visible surfaces. On a bottom rail, a hole on the underside near each end and at low points lets water leave without running down the face.

Internal coating adds a second layer of protection. Some shops use tube that has been galvanized inside and out, or spray a rust-inhibiting primer inside before assembly. Zinc-coated tubing resists internal corrosion well, even if some water enters.

Weld seams should be continuous where sealing is the goal, and ground smooth so coating covers them. Intermittent tack welds along a seam leave gaps that act as channels.

Ends should be capped or plugged with a material that will not shrink and loosen. Plastic plugs are common on pickets and may work well, though they can fall out over time or crack in strong sun. Welded steel caps stay put.

Checking an existing gate

Owners cannot see inside a tube, but they can look for evidence of trapped water. Rust-colored streaks below joints, at the bottom of pickets or under the rail are warning signs. Bubbling paint near welds and at the lower ends of vertical members suggests moisture trouble. Tapping along a tube with a screwdriver handle helps: sound metal rings, while a section with water or thinned walls sounds dull.

On a gate that has weeping rust at its lower joints, the cause is often an undrained section. A small drain hole drilled by a qualified fabricator at the low point can release the water and prevent further damage, though the interior may already be corroded.

Any drilling should be followed by touching up the cut edges with primer and paint, since bare metal at the hole would otherwise rust. A fabricator will also check that the hole is placed to drain and not on a surface where water would run back in.

When to ask the fabricator

For a new gate, a few direct questions reveal the builder's care.

• Are the tubes sealed or drained, and how?
• Is the tubing galvanized or coated inside?
• Where will drain holes be, and how are they kept from marring the finish?
• How are tube ends closed?

A shop that answers confidently, and can show a cut-away sample or photograph, usually builds with long life in mind. A shop that has no answer, or says it has never thought about it, has probably not planned for the problem.

Small detail, long life

Attention to drainage and sealing costs little at the time of fabrication and saves a great deal later. A few tiny holes drilled in the right places can add many years to a frame. For anyone buying or maintaining a metal gate, this is one of the quietest and most valuable details to look into, and it applies to every hollow member, from the largest post to the smallest picket.