Wive's tales about
stucco and plaster


Galvanized lath on copper or aluminum flashing
causes a transfer of metal that is (somehow)
harmful to the flashing or the stucco.

This is true- in plumbing. When a galvanized pipe is coupled with a
copper pipe, a slow transfer of metal occurs that leads to the pipe
leaking. This can be remedied by attaching a diode connected to
both pipes to control the metal transfer. This diode ( or device)
needs to be replaced every so many years to assure reliability.

There is no need for a pressure tight or water proof seal between
the lath and the flashing. Galvanized lath doesn't accelerate oxidation
on copper or other dissimilar metal.

PROOF: I examined several houses built in the 1920's and
1930's that had copper flashing and galvanized lath and stucco
and the original flashing was still in good shape.
I hear this all the time. I think it was started by the EIFS people.

Lime in plaster etches glass

The plaster finish coat is lime and gauging plaster, or mostly lime.
Lime does not etch or affect glass in any way. What scratches
glass is a careless person scraping windows.

Romex (plastic insulated electrical wire) cannot be plastered

over because the plaster has lime that eats the plastic.

Lime does not eat plastic. Plaster base coat (brown mortar)
has no lime at all, contrary to popular belief, but is made from
gypsum and sand. Electrical channels, where grooves are cut
into the old wall are generally patched with lime and gauging
plaster (white mortar).

There are some dangers to doing this. With no conduit to protect
the wire, someone may try to drive a nail in the wire, damaging
the wire and creating a short. Also, with no conduit the wiring
can't be changed in the future,

Lime is caustic, but it is alkaline, the opposite end of the ph scale from
acid. Acid is sold in plastic jugs.

Lime doesn't eat plastic insulation on wiring. It says it does in the
National electric code.