Point 10 of my 12 point list of methods for reducing cracking in

 portland cement stucco




Point 10 of my 12 point list of methods for reducing cracking in portland cement stucco.

Point ten - Good lathing

                furring lath
                     Self furring lath
Deep cracks and loose areas caused by bad lathing are  impossible to repair, without the repair coming back to haunt. 

The reasons for metal lath are: 
1. Support (to hold the mortar up) 
2. Reinforcement -increased tension strength 

 Self furring lath has punches 1/4" deep, or "furs" to hold the lath away  from the wall. This allows mortar to penetrate well behind the lath for good support and good embedding of the lath for reinforcement. 

I see flat lath used sometimes for stucco. Although the mortar 
will hang on enough to hold it on, it is still an inadequate method. 

Out west they use self-furring stucco mesh. Some brands have the punches painted with a dot of yellow or red paint, for easier alignment to the studs. In California they call the diamond mesh lath we use here, "K-lath". 
                  nails for metal lath
An old lath nail was made for "hanging" welded wire lath. The nails were never driven tight, allowing mortar to key behind the wire.

Doing restuccos, we find different techniques used by our forefathers for furring lath. 

One method was driving U shaped nails in the wall about 12" apart. When the lath was put on it was the nails were placed directly over  the first nails, allowing the first nails to hold the lath away from the wall.
Another method was nailing small wood blocks, such as wood lath strips cut into 2 inch pieces to the wall and nailing the lath to the blocks. 

Furring strips don't work

Furring strips don't work
This wall was furred with furring strips,
 and failed over the years.

Mortar doesn't key behind the strips, forming a long weak area that is liable to crack. These strips here weren't strong enough to permanently support the stucco.This wall had failed and had  been patched several times over the years. 
Furring strips do work with self-furring lath.
                  "laps" in metal lath
           Tying "laps"
Where no sheathing is used, such as this interior plaster installation,  the "laps", or where the lath overlaps in between the studs, should  be tied with tie wire at least two ties  between the studs. Failure to do this will lead to nasty cracks. Mortar must key into both pieces of lath to prevent separation. 
                  metal lath
      3 inch over laps.
The standard for the minimum overlap for metal lath is one inch, but I say, why be cheap? Go 3 inches. Note how the inside and outside corners are reinforced with strips. There is a pre-made material for this called cornerite, which is pre-bent strips of lath. 
Crack resistant work begins with good lathing.