A.John Leeke, a preservation consultant from
Portland, Maine, responds: To join straight gutter
sections, I usually use a miter joint, fastened with screws and
adhered with epoxy adhesive formulated especially for wood.
The most effective way to seal butt and miter joints is to
form a groove along the joint, inside the gutter, and to fill
the groove with a sealant. The groove provides a space for
enough sealant to make the joint flexible, allowing for
expansion and contraction.
One way to create the groove is to rasp a 1/4- to 3/8-inch
bevel at the edge of the joint. For better performance, make a
"designed joint" by routing a rabbet at one side of the joint
(see illustration). Apply release tape to the bottom of the
rabbet, or insert backer rod, and then install the sealant.
This type of joint will let the sealant flex more that the
plain bevel joint. Since no sealed joint will last forever, I
drill a weep hole at the bottom of the rabbet to let water out
of the joint. Once the joint begins to leak, the weep hole
helps prevent decay, and acts as a tell-tale sign, indicating
it is time to re-seal the joint, as part of ongoing
The traditional way to flash these joints is with lead
flashing installed in the gutter trough. Thin sheet lead
flashing is better than thicker flashing, because it is more
flexible in service. I start by forming a 4-inch-wide lead
strip to the contour of the gutter trough, so it laps over the
joint 2 inches on each side. Then I scribe the wood surface
along the edge of the lead and chisel out a depression so the
lead sits flush with the trough surface. I seal the lead down
with flexible sealant along the edges and fasten it in place
with galvanized steel or lead-coated copper nails, which I coat
myself. If plain copper nails are used, the lead is subject to
corrosion due to electrolysis.
A leak-proof outlet can easily be formed with lead pipe. I
can usually find thick-walled lead waste pipes right on
renovation projects, whenever an old sink is being ripped out.
New lead outlets with a flange already formed are available at
some building suppliers.
A flush lip on the outlet will allow all the water to drain
quickly. First, I drill a hole in the gutter about 1/8 inch
larger than the pipe. With a ball peen hammer I gently form a
1/2-inch lip on one end of the pipe. I shape the lip so it lays
flat on the trough bottom all around. I scribe the trough to
show the outline of the lip. Then I chisel a depression for the
lip, so it sits flush with the surface of the trough. Finally,
I seal the lip in place with sealant and fasten with 1-inch
galvanized steel or lead-coated copper nails.
At the high end of a gutter, I make end caps out of
3/4-inch-thick wood. A simple sheet-metal flashing is not
likely to hold up to years of gutter cleaning. At the lower
end, I usually install a complex sloping piece of lead
flashing, to make sure the short length of gutter from the
outlet to the low end drains back into the outlet.
Wherever end-grain has been exposed — at the various
cuts, rabbets, and holes — I seal the end-grain with
epoxy consolidant before priming, painting, assembling,
sealing, and flashing. This prevents one of the leading causes
of wood gutter decay, which is end-grain water penetration. I
usually use a one-part polyurethane high-performance sealant,
like Sonneborn NP 1.