I need to attach what would look like a small shelf (2"a x 3"b x 4"hyp): to
a plaster wall. It is to support a magnifying lamp with a clamp-on pivot
arm. The lamps weight is a bit of a beast. The shelf itself is not a
problem, I can make it out of 3/4" plywood, but I do not have experience
with this type of wall. It is not drywall, its the kind of very hard to
knock on stuff, from 70 yrs ago. The small shelf is a <||>, turned 90
degrees, for a beast of a clamp-on pivot arm to the || shelf. A small
horizontal shelf dadoed into vertical pieces bolted into an inside corner
wall will withstand the torque stresses. I have a 1/2" hammer drill and I
will need to drill into the normal wall (inside corner) both above and below
the shelf at right angles so the clamp-on pivot arm torque forces on the
shelf will be pushing on the shear of the four fasteners. The distance from
the adjacent wall will have to be the width of the 1/2 profile of the hammer
drill (maybe 2" from the inside corners, about 27" up a 8' high wall). I
have a feeling I will need to build a jig for the holes, probably with
plywood with washers hammered in spaced spade drill holes, so the masonry
bit doesn't jump all over the place. So I will be using masonry bits, but
since I have never attempted such a hold, not drilling in this type of wall,
I don't know what type of fasteners to use, or if I need to worry about
drilling out with HSS-type regular-drill for lath or whatever might be in
there from before I was born.
So the question is:
What's in there & how do I drill it out (several drills, drill holes in wood
What kind of fasteners do I use through 3/4" plywood & into wall (lag bolts,
I don't understand much of what you wrote but plaster walls will have wood
lathing behind it. (strips of wood that the plaster was applied to) You won't
need a hammer drill. If you're going to use a mansonry bit it will also go
through the lathing. You won't need a jig. Lag bolts will not work. I like to
use the type that spring open (can't think of what they're called right now)
after you push them through the wall. If the plaster wall is in good condition
it will withstand a lot of stress/torque. Also, you might want to hunt up a
stud to screw directly into.
I am assuming that he thinks he needs a hammer drill with masonry bits to get
through the "very hard" plaster and then possibly switch to an HSS bit to get
through the lathing strips or "whatever might be in there."
Drilling into a plaster wall isn't difficult. Just use a normal drill and a
regular steel drill bit. Plaster is harder than drywall, but it's still
quite soft compared to steel or stone.
Mark your holes, and start with a small drill bit. Then switch to the full
size bit, or work your way up to the full size with intermediate sized
If this is a normal plaster over wood lath wall, I would attempt to find a
stud and use screws long enough to go through the shelf, the plaster, the
lath, and into the stud (a 2-1/2" to 3" screw should be fine).
An electronic stud finder works OK with plaster walls too, just double and
triple check in multiple places because the varying thickness of the
plaster can sometimes give false positives.
If there isn't a stud where you need to insert a fastener, use the spring
loaded moly type bolts. Drill a small hole through the shelf and wall, then
take down the shelf and widen the hole in the wall so it's big enough to
pass the moly through. Assemble the bolts on the shelf, then holding the
shelf to the wall, carefully push the moly's through the holes. They'll
spring out on the back side, and you can pull them tight against the wall
while you tighten the screw. If it's a heavy shelf, you might need to get
some help with that.
If the plaster is over a masonry wall (concrete or brick), you'll probably
need to drill the holes with a masonry bit (start small, work your way to
the needed size), then use expanding masonry bolts.
Hope this helps,
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