Stucco News

Questions and answers on Stucco and Plastering-- May, 2014




     Metal lath and mechanical keys

for stucco and interior plaster.

A gap was left in
                          between the lath strips allowing mortar to be
                          forced through to form keys.

An old wood lath and plaster application
shows how plaster was supported.

A gap was left in between the lath strips
allowing mortar to be forced through to form
keys.


Wood lath stucco base
A closer view of the
                          bevel cuts.
Wood lath stucco base had the edges chamfered back for mortar keys when the lath was put on a substrate like sheathing or tarpaper.
A closer view of the bevel cuts.
Angle cuts allowed
                          mortar to key
An old house in the
                          Brookland area of Washington, DC shows stucco
                          base in action.
Angle cuts allowed mortar to key, even when
even when the lath was put on tight against a flat substrate.
An old house in the Brookland area of Washington, DC shows stucco base in action. The tarpaper was removed during major repairs from flood damge.


                    About Metal lath and cement floors (mud base).


Floor joists where
                          chiseled off at an angle for a metal lath and
                          cement floor.
The joists were chopped
                          down forming a point.
Floor joists where chiseled off at an angle
for a metal lath and cement floor.
The joists were chopped down forming a point.
splitting the joists at
                          an angle allowing mortar to form full keys.
flat areas form weak
                          spots in the floor, leading to cracking and
                          failure.


An illustration showing how splitting the joists at

an angle allowing mortar to form full keys.
Without cutting off the joists at an angle, the flat
areas form weak spots in the floor, leading to cracking and failure.
It really gives me a pain to see someone put
in a mud floor using flat lath and stiff mortar on plywood.
The metal lath offers no reinforcement this way.
You may as well just pour mortar on the plywood with no lath.
Chipping was used many years ago to
                          plaster over old walls.

       You may have seen our chipping method before.

Chipping was used many years ago to plaster over old walls.
      
In old buildings, I have found this plaster easy to knock off. Chipping alone isn't enough to bond mortar permanently to an old wall.
     
A chemical bond is used along with chipping to ensure a permanent bond.
    
The point is that holes are made allowing some mechanical key for the plaster.