Bonding agent failure

Ask the pros-December, 2003
By Reggie Bullard

Bonding agent failure.

 I am an attorney in Miami, Florida dealing with a stucco delamination issue on a hotel in Miami Beach.  I need a stucco guru who can communicate to ordinary people.  Are you aware of any delamination problems caused by exterior use of Larson Plasterweld, Lambert Bondrite Liquid or Florida Laboratories Chemweld.

Chemical bonding agents (paint on type), painted on over painted stucco and sometimes porous unpainted stucco will fail over time. Work we did this way years ago is all loose and popping off. 
Stucco bonding agent failure
By the time I got back with my camera,
 this wall was already torn off.

Plaster weld was painted on the old painted stucco and
 the new layer
of stucco was loose and popping off.

It is real embarrasing to think we used these bonding agents years ago,
and all the work we did is loose and popping off. I stopped using these
bonding agents when I discover work we had done 10 years before
was already failing. I felt we were doing the customer a service by 
saving money. All I can say is I'm sorry, I just didn't know, even though
it is a frequent practice to use them.

The practice of using these bonding agents still goes on here in the 
Washington area and I'm sure other places. If you are a plasterer
using this method, I suggest you stop immediately. I have seen 
buildings around Washington that are pink(or blue) with bonding agent
and the stucco has popped off, or was scraped off. Pretty sad for
what should be a permanent application. If you want evidence, write 
and I'll send you addresses you can ride by and see.

My solution to recoating painted surfaces or old stucco is to use an
Acrylic bonding admixture, but first removing the old paint, at least 90
per cent. Then a bonding coat applyed by mixing acrylic like Flex-con
50-50 with water, portland cement and sand. A thin coat is then applyed
leaving the surface rough by using a float, combing with a trowel or
even a brush. After the bonding coat sets at least overnight, a finish coat
can be applyed.
bonding coat with bonding admixture for stucco
Here a bonding coat is applyed after the failed stucco
and coat of the paint is scraped off.

There are other methods of appying a bonding coat, such as mixing 
pure acrylic with portland cement( no sand) and applying with a stiff
brush or a broom. The important thing is that the surface is left rough
with open pores for a good bond with the finish coat.

These bonding agents are excellent for indoor plastering, they eventually
fail on the exterior because rain will eventually soak into the stucco
and dissolve them.


Stucco news home    monthly column: No 9 in my 12 point crack attack   next question