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Painted stucco San Miguel de Allende Mexico (C) Daniel FriedmanStucco Finish Bonding Agents

Use of stucco & cement bonding coats & admixtures

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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Comments

Juergen · Nov 7, 2023

I have a concrete turret covered with stucco.Because of cracks in the upper part of the stucco,rain got behind the stucco and now the stucco looks like a loose wallpaper. Can I push some bonding agent between the stucco and the block wall? Then press the loose stucco and the block wall together?

InspectApedia Publisher (mod) · Nov 8, 2023

@Juergen,

Well you could try that by drilling injection holes and squeezing in construction adhesive, but I'm very doubtful that that will be a durable repair.

More likely the turret will need to be re-stripped and re-stuccoed.

But first, let's diagnose just why the stucco failed: where were the leak points? Bad flashing?

Post some photos so that we can take a look - one image per comment.

Dorothy - re-posted without link (mod) · June 28, 2023

Dorothy · 1 hours ago

Hi.

I have a 1980's house that is part traditional (not synthetic) stucco, part faux-Tudor wood trim, and part brick. The wood is in bad shape, and the stucco is full of patches and was painted at one point with acrylic paint.

Some of the patches are just a close color to the acrylic paint but are not painted. The acrylic paint is in good shape.

Since the wood trim is in bad shape, and I live in a "red zone" at risk for wildfires, I would like to it all removed. I had a couple of the horizontal pieces of wood trim removed, patched and re-textured. They are ok. Then I had some vertical wood trim removed and those patches are not great in texture match and some cracked. There are some additional small cracks here and there.

On that work, stucco was mixed on site (not a pre-mixed patching product) More recently, the process on removing vertical corner wood trim (just had one done and I watched how it was done) involved the use of a pre-mixed product with fibers in the mix. The base/brown coat / patch material was applied over Pro-Wrap and wire. Then the cement mix (with color added into that) was mixed on site, applied and textured.

Was that the best way of doing that? The textured top layer was feathered out onto the acrylic-painted stucco, and I worry that without a bonding agent, the feathered parts will just interfere with the re-dash. I've come to the conclusion that the only way forward is to continue replacing the wood in the same way as that first corner. But then having it followed up with a bonding agent then a complete exterior resurfacing (re-dash) as shown in this video: [deleted]

I really don't like the heavily-textured, lacy texture currently there. I'd rather have a plainer texture, so a re-dash would give me the opportunity to change the texture and get the whole exterior uniform and refreshed with a cement color coat that won't need painting in the future.

My biggest concern is applying a bonding agent to a heavily textured finish. I know it has to be thin to avoid issues with the final finish (per the video linked to above). But a thin layer of bonding might not work with a highly-textured finish? Please let me know your opinion on all of this. Also, what would be the easiest texture to match in the future without it sticking out like a sore thumb? Not everything that needs to be done on the house exterior is going to line up to avoid future patching. The 1/8 inch top coat will be Lahabra if that makes a difference in your view of the matter.

Thank you for any advice you could share on this.

InspectApedia Publisher (mod) · June 28, 2023

@Dorothy -

I watched the video whose link you included - it's principally focused on re-coating a stucco walled home at which various repairs and work done over the years resulted in textures that vary from one wall section to another. The author, Kirk Giordano of Kirk Giordano Plastering Inc., calls it "bad stucco patches" posts lots of videos on plastering methods. To be clear, Kirk knows a lot more about plastering than I do - probably having done many more jobs than I did.

That said, where your concern is for the successful use of bonding agents, my solution is to read the instructions on the product label.

I've used paint-on bonding agents on rough surfaces and found that they worked very well.

I've also used add-in bonding agents mixed with my cement or plaster - depending on the job - that in my OPINION may give a more-durable reply where patching or re-coating.

For other readers: an exterior plaster wall "re-dash" job refers to re-coating the entire wall surface with a new layer of stucco using portland cement to which the desired coloring agent has been added.

In my OPINION the success of any re-dash job begins not with the choice of additive - I figure that the thickness of the re-dash stucco layer will be adequate to cover irregularities and inconsistent patterns in the existing stucco wall.

Rather success begins with a careful inspection of the condition of the stucco on the building exterior.

In particular, Kirk's video shows a home where the stucco exterior looked to be in sound condition - I didn't see cracks, bulges, loose or missing stucco. That means that the re-dash job has a sound base over which the new stucco layer will be applied.

Of course you're not going to stucco over loose dirt, rain splash-up debris etc.

On the other hand, most of the stucco homes I worked on had a wide range of conditions of the exterior stucco including cracks, bulges, fall-offs, and areas of soft stucco that was perhaps a poor mix in the first place. We made a point of correcting all of the underlying causes: roof drainage mistakes, settlement, loose lath, etc. before even starting to repair or re-dash a stucco exterior wall.

Perhaps you can post some photos of wall areas that are of concern on your own home.

tMtFQiRt · Nov 21, 2022

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