Jim from London, Ontario writes: "I have a 30 year old home and the metal gutters have never been replaced. Certain sections seem to have rusted through and have developed pin to dime size holes that leak. I have tried to patch them but nothing seems to stop these small holes from re-occurring. Do you have any suggestions, short of replacing the gutter?"
Just patching small holes often still lets the water get to the edge of the patch and continue corroding from there.
The best way to patch those holes is to thoroughly clean off the holes and even the area around them inside the rain gutter, going at least an inch beyond any sign of corrosion.
Use steel wool for this cleaning to be sure you have removed all the accumulated grim that usually sits in the rain gutter.
Then obtain a piece of aluminium flashing (you can get this at all renovation centres, although you may have to buy a roll), or cut off a piece of thick aluminium sheet metal from something else (not the thin cooking trays).
Use PL Polyurethane caulking to completely coat the bottom of the rain gutter in the area of the patch, making sure that it is worked into the surface as sometimes it can just ride on the surface. Put a thin layer on the patch as well just like if you were using contact cement. This will assure that there are no adhesive voids.
Force the two together and let it set.
One convenient thing about PL Polyurethane caulking is that you do not have to do this in dry weather. The surface must be clean, but not necessarily dry -- just no standing water.
The water will actually accelerate the cure of the Polyurethane.
I recommend using PL Polyurethane Sealant, not PL Premium Adhesive, as the sealant will remain flexible and the adhesive becomes rigid. You need the flexibility to be able to move with the expansion and contraction of the rain gutter.