First,
measure the needed cutout size in square form. Say, 1’
by1’. Using a utility knife, cut out this 1’ given
square section on your spare piece of drywall. Then, overlay
the shaped section directly on top of the area to be cleared
for affixing the patch. Hold it there, trace its border with
a pencil, always taking special care as to wall cavity wiring
and other potentially dangerous obstructions - cut the marking
out with your knife, only as deep as necessary.
Proceed
then by cutting (4) strips of fiberglass tape that will extend
either way off the drywall edge at least a couple inches beyond
your cutout size, from behind, about 18 inches total each
piece for our example.
With your
compound, liberally back-butter the wall board. Place your
(4) cut fiberglass strips in sets of parallel two, each in
ways of direction that cross each other at ninety degrees,
while atop the compound on this backside and press the strips
down firmly in order to embed them.
Tilt your
cut-out up in place, and pull the fiberglass strips outward
to fairly taut, leveling the board surface with the wall as
you go. Once a level is achieved [slightly sunken better than
risen] firm the strips to the wall. A screw in a convenient
stud will usually help but that is the beauty of this patch.
It can work without nails or screws. Float a layer of your
bedding compound then smooth with topping mixture.
Final
top coat the patch at least once, sand to a smooth plane and
finish to desired color and texture. Check on your hvac
filter after competion.