How to Repair an Aluminum Boat Hull & Transom

Start by cleaning the area with a wire brush and solvent to remove algae, oxidation, and grease. Inspect the crack length and depth. A hairline surface crack on the exterior may run deeper on the back side — check both inside and outside the hull.

For transom cracks, look for delamination around wood or composite cores. If water has seeped into a wood-cored transom, the damage is structural and welding alone will not fix it — the core must be replaced.

For a short-term patch on the water or at the ramp, marine-grade epoxy putty or an aluminum repair patch kit can slow a leak. These are stop-gap measures only — they do not restore hull strength and will fail under vibration and heat cycles.

Proper prep is what separates a repair that holds from one that cracks again in six months. Aluminum oxidizes almost instantly, so cleanliness is critical.

1. Grind away paint and anodizing around the damage with a flap disc — extend at least 1 inch past the visible crack on all sides.
2. Chase the crack with a carbide burr or grinding bit to create a V-groove. This gives the weld something to bite into and removes contaminated base metal.
3. Clean with acetone or lacquer thinner immediately before welding. Do not touch the bare metal with bare hands after cleaning — skin oils will cause porosity.
4. Clamp or brace the hull to prevent warping from heat. A backing bar of copper or aluminum on the back side helps control heat and supports the weld pool.

Aluminum TIG welding requires an AC-capable machine with high-frequency start. Use 100% argon shielding gas and 5356 or 4043 filler rod (5356 is stronger and more corrosion-resistant for marine use).

For cracks: Tack each end first to prevent the crack from spreading. Weld in short 1-inch bursts, allowing the metal to cool between passes. Overheating will warp thin hull material (typically 0.080–0.125 inch).

For holes: Cut a matching aluminum patch from the same alloy and thickness. Bevel the edges of both the patch and the hole, then TIG weld in overlapping stitch passes. A copper backing block is essential to prevent the weld from dropping through.

After welding, let the area cool naturally — do not quench aluminum with water. Rapid cooling can introduce stress cracking.

1. Grind the weld flush with a flap disc if the repair is cosmetic. For structural joints, leave a slight crown for strength.
2. Wire-brush the heat-affected zone to remove oxidation. A stainless steel brush dedicated to aluminum prevents contamination.
3. Apply marine-grade sealant or epoxy primer to protect the bare metal. Anodized aluminum does not need paint, but raw welds will oxidize quickly in lake water if left unprotected.

DIY aluminum TIG welding is possible with the right equipment and practice, but most boat owners do not have an AC TIG setup, the correct filler, or the experience to avoid common mistakes like porosity, lack of fusion, or warping.