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DIAGRAM #1
Floating joint compound over pre-taped cracks, feathered
out about six inches on each side of the crack
DIAGRAM #2
Plaster washers can be used to secure the loose or high side of cracks to the lath
in areas where keys have failed
DIAGRAM #3
It is sometimes necessary to open a bulge with a wire
and vacuum any debris from behind the plaster in order for it to set flush against the
framing again. |
CRACK REPAIR:
Hair-line cracks that have been around for years are easiest to repair. Remove
any loose particles from the crack, apply a coat or two of joint compound or spackle,
allow to dry, and sand the area smooth with sandpaper and a sanding block.
If this fails or the cracks are larger, taping and floating the crack
with a thin layer of plaster is required. Before you perform this operation, certain
things should be checked first. Check to see if one side of the crack is higher than the
other or if the plaster is also loose. If the edges are even and there is no loose plaster
simply tape the crack with self-sticking fiberglass tape following the crack where it
leads. Do not worry about overlapping tape ends. Once the tape is in place float two or
three layers of thin joint compound or Durabond, allowing it to dry between each
application. The joint compound should be feathered out about six inches to each side of
the crack. After the last coat has dried, sand smooth.
If the edges are not even or there is loose plaster, dig out the crack
down to sound plaster. Plaster washers may be needed to secure the plaster to the lath or
studs if loose plaster extends too far beyond the crack. (see diagram 1) After loose
material is removed, apply a plaster bonding agent around the edges. Fill in the excavated
crack with Durabond, allow to dry and then follow the above directions for taping and
floating.
For extensive cracks or map cracking, calling a professional may be the
best option for most homeowners. However, if you feel you would like to do the work
yourself, cover a large area with sheets of adhesive-backed fiberglass mesh or embedded
sheets of fiberglass window screening in Durabond. When this is dry apply another coat and
finish with bucket mud or Easy Sand.
DELAMINATION:
If the
finish coat has delaminated, remove all loose debris down to the brown or scratch coat if
necessary. Following manufacturing directions, apply a plaster bonding agent to the
damaged surface. Trowel on the finish coat with veneer plaster or multiple coats of
Durabond. As the plaster begins to dry, brush it with water and quickly smooth it out.
After it dries, apply a final coat of drywall mud over the plaster and sand smooth when
dry.
KEY FAILURE:
When key
failure has occurred, all loose plaster must be removed down to the lath. It is usually
easy to find a stopping point where the plaster is in sound condition. Sometimes, however,
you must take care not to use too much force and damage sound plaster. Screw in plaster
washers around the damaged area about two inches from the edge and four inches apart. If
there is damaged lath it must be repaired by bridging over it with metal lath mesh secured
to the wall framing.
Once the area is clean apply a plaster bonding agent to the edges and
lath. After the bonding agent is dry, apply a scratch coat of Structo-lite plaster with a
trowel, pressing it into the lath to create new keys (See diagrams 4). Scratch the surface
with a nail, as this will help the brown coat bond properly to the scratch coat. The next
day, the brown coat can be applied, also using the Structo-lite. You can use veneer
plaster or Durabond for the finish. If you use veneer plaster leave the brown coat about
1/8 inch from the surface. If you use Durabon, bring the brown coat almost flush with the
surface. Prepare the surface by dampening with water before applying the finish coat. When
the finish coat has been trowled on and dried, any small imperfections can be patched over
with drywall mud. Remember to make sure that all surfaces are cleaned of dust and debris
before each application of any of the three coats or touch ups.
ROCKING A PATCH:
An
alternative to a three coat patch is "rocking a patch". If the thought of going
through the three layers of patching seems a little too difficult, use rock lath or
drywall (see diagram 5).
 Rock lath is similar to drywall, however it is chemically treated
to bond to veneer plaster. Cut a piece of rock lath to fit the hole as snugly as possible
and secure it to the lath with screws. Apply a plaster bonding agent to the edges of the
old plaster and the rock lath. Fill in the open gaps with Durabond or
Structo-lite. Tape
the seams with mesh tape overlapping the gap between the old plaster and the rock lath.
Then you are ready to float out the area with veneer plaster until it is even with the
surrounding surfaces. Make final patches as need and sand smooth.
DIAGRAM #5
For
larger patches it may be easier to use rock lath or dry wall to fill in the larger portion
of the void and then applying a finish coat.
Dry wall comes in 1/4, 3/8, 1/2, and 5/8 inch thicknesses. If one of these sizes is not
appropriate you can use a combination of more than one layer to fill in the patch.
With drywall, finish with multiple coats of Durabond and a final coat
of bucket mud or Easy Sand.
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