Proper caulking is vital to window installation success. Even if you
carefully follow every other aspect of proper installation, a poor
caulk job or the wrong choice in caulking product could yield disastrous
results. Caulking is also important for effective window insulation
–for both warm and cold months of the year.
To avoid mistakes
that could prove costly, note the following important tips:
- When gaps between the window frame and wall surface exceed 7/8
of an inch, use solid fill strips to make gaps narrower before
caulking. Likewise, when the depth of gap is deep, use foam backer
rod or another type backup material to partially fill the cavity
- When caulking, install the product to the proper depth using
a continuous bead, free from voids. Beads should be about as half
as deep as they are wide, and bead depth should never exceed bead
- Before caulking, carefully rid the area of any old caulk, dirt,
oily substances, moisture, and any other debris which would prevent
the caulk from properly adhering.
- Follow the window manufacturer’s recommendations when
selecting caulk; a waterproof product made specifically for exterior
- Caulk formulas made using polysulfide, polyurethane, and silicone
provide the best seal for window installation and will adhere
well to most materials while still remaining flexible. This is
especially important for the top of the retrofit unit to prevent
damage to the frame should the header flex or sag.
- The wrong type caulk on vinyl window frames could not only
compromise the seal and stain frame fins, but cause severe damage
to the frame, as well. In some instances, dissolving the vinyl.
Use only caulk formulas recommended by the window manufacturer.
- If you plan on painting the exterior of the new window frame,
make sure the caulk you use can also be painted, or that the color
caulk will be compatible with surrounding materials.
- Pick a day to install the new window when temperature is mild,
and within the range required by the caulk used for a successful
seal. Note: changing temperatures cause joints to expand and contract.
Applied on too-hot surfaces can cause caulk to tear once substrates
contract in the winter. Applied in too-cold weather can cause
caulk to become over compressed by substrate expansion during
Next, be sure and caulk in all the right places, otherwise the window
- Finned windows should be caulked around the entire fin perimeter.
- Caulk corners of mechanically joined frames and other joints
where leakage could occur.
- Caulk any wood strips installed to fill gaps left where siding
was removed – except when finishing trim has been installed
over shim strips. In such instances a neat bead around the edges
suffices and will look more professional.
- Caulk the gap between the window frame and the opening of boxframe
windows using one continuous bead, free of bubbles.
- Caulk gaps between the edge of the siding and rough opening.
However, never caulk weep holes in the sill jamb; these are important
for condensate drainage.
Remember, improper caulking procedures compromise the entire window
installation process and leave your home vulnerable to unnecessary
energy loss. A seal that does not adhere properly will not be weather
tight, and can result in moisture penetration and water damage.
The area around the window frame will not be well insulated, resulting
in less effective internal heating/cooling efforts.
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