A large variety of items are made out of cast aluminium, including cars, motorcycles, boats, porch furniture, pipes and gutters. The reason aluminium is so widely used is because it does not corrode easily and therefore is a choice metal for objects used outdoors. Unfortunately it is also a relatively soft metal so it is easily dented, cracked and broken. You can repair cast aluminium by melting an aluminium razing rod to patch any imperfections.
Clean the area thoroughly. Use a wire scouring sponge and a heavy-duty metal cleaner to remove any dirt and grime from the aluminium you are patching. If you are reattaching two pieces of aluminium that have broken apart, such as a furniture leg, clean both pieces. Wash off the cleanser with water and dry the aluminium. Any foreign substance on your object will keep it from binding with the new aluminium.
Light your torch and hold it to the area that needs to be repaired. The area must reach 391 degrees Celsius in order to melt the aluminium brazing rod. Do this outside or in a well ventilated area. Melting aluminium gives off a harmful fumes.
Hold the aluminium brazing rod in steel tongs to protect your hands from the heat. Rub the brazing rod on the heated part so it begins to melt. If you are filling in a dent or hole, allow enough aluminium to melt so it fills the area. If you are connecting two pieces of aluminium back together, melt enough of the brazing rod just to cover the area of one broken end. Stick the other broken end to it and clamp into place. Allow the aluminium to cool.
Smooth down the repaired area, starting with a coarse sandpaper and moving to finer sheets to polish. You can also use a metal buffing tool. Hide the repair with a coat of paint or polish.
Wear the necessary safety gear while using your torch.