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Painted stucco San Miguel de Allende Mexico (C) Daniel FriedmanStucco Finish Bonding Agents
Use of stucco & cement bonding coats & admixtures

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Instructions for using bonding agents on stucco or concrete surfaces:

This article series describes common building exterior & interior painting mistakes when painting on modern stucco building exteriors, describes how to diagnose paint failures on buildings, and outlines a procedure for diagnostic field inspection & lab testing of failed painted surfaces.



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Use of Bonding Agents in Stucco Applications

Stucco wall stains after painting (C) Daniel FriedmanThe use of bonding agents can improve the adhesion, life, and performance of stucco and concrete surfaces and their coatings. But choosing the wrong bonding agent or failing to follow the manufacturer's instructions when applying a bonding agent can lead to ugly stucco and concrete coated surface failures or to paint failures.

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Question: is it ok to apply stucco, bonding agent & top coat all in the same day?

2017/09/27 Mike Bell said:

I have a question. I recently hired a stucco contractor to patch a couple of fairly large areas on the exterior of our home where windows were removed and "walled in".

They applied a single layer of traditional stucco, about 3/4" thick, followed a short time later the same day by a blue-colored bonding agent and then, after about an hour, a finish layer of acrylic stucco.

Is this approach ok? Will the traditional stucco cure properly behind the acrylic layer and, if so, how long should I wait before priming and painting with an elastomeric paint? Thank you.

This question and our reply were posted originally at PAINT on STUCCO, FAILURE

Reply: probably not

Mike,

Thanks for a good question. The use of a bonding agent in the stucco system being used to repair your home might be perfectly correct - or not - depending on the specific stucco product being used.

It is also important to select the right bonding agent for the application: outdoor agents for outdoor use, for example.

The manufacturer will almost certainly have an opinion about whether or not they want a bonding agent to be used. Bonding agents used with portland-cement based stucco and that are painted onto a surface or onto an intermediate coat are specified by ASTM C932.

Some of the stucco instructions I reviewed to address your question recommend use of a bonding agent but specify that a minimum cure time of 24 hours is needed between coats.

Here is an excerpt from an industry expert:

On two-coat work, only the base coat is bonded to the substrate. It should be at least three-eighths of an inch thick and permitted to dry a minimum of 24 hours.

This is extremely important. If the second coat is applied too soon, the moisture may penetrate the scratch coat and flood the still wet bonding agent and cause a delamination. - (Larsen 1995)

Bull-Bond™ for example warns that the base concrete layer needs to be "cured to industry standards" (perhaps 24 hours) before applying the bonding agent; the top coat is then applied over the bonding agent as soon as the bonding agent itself has "cured" - typically meaning when it feels dry to the touch.

If you can find out the product name that was used on your home we can perhaps find an answer that fits your specific case.

A different type of product, integral bonding agents that are mixed in with the stucco itself should not be used unless the manufacturer of the stucco system agrees with that application.

Past the question of proper application of the stucco repair patch, bonding agent, and top coat layer on your home, before you paint the new stucco area, wait at least 10 days to permit the stucco to cure, and also review our curing, sun and wind warnings, and other painting advice and caveats in the article above.

Research on Use of Bonding Agents for Cement / Stucco Applications

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