Akhnaten reached out with concerns about cracking and telegraphic rust spots appearing on a stucco wall. Let’s explore potential causes, solutions, and whether a complete redo is necessary.
Question from Akhnaten:
Greetings. This stucco wall is experiencing cracking and also telegraphic rusting spots. While the rust spots are appearing randomly, they do somewhat appear to be uniform in spacing.
At first, we thought it was a rusty fastener coming through; however, it wasn't. It is something called lignite. This is the south-facing wall with a lot of sun exposure. The other walls around the building don't have this issue. I suspect the sun exposure is accelerating a chemical reaction with the chemicals in the stucco mix.
One installer mentioned if a trowel was used on this application that was not stainless steel, it can present these spots periodically over time. What is your experience with this, and what solutions do you have to address this phenomenon? Must the whole wall be demo'd and redone? Is a topical solution available? Pics and detail attached. Thx.
Answer:
Hi Akhnaten, thank you for the detailed question and photos. This issue is definitely unusual, but let’s break it down to better understand the problem and potential solutions.
Identifying the Cause of the Rust Spots
The rust-like spots you’re seeing could indeed be caused by lignite or other impurities in the sand or materials used in the stucco mix. It’s also important to determine whether the staining is isolated to the finish coat or if it extends down to the base coat.
This investigation will help identify the depth of the issue and the extent of the repairs needed. Here are a few thoughts off the top of my head:
- Lignite in the Sand: Lignite is a naturally occurring material often found in some sands. When exposed to moisture and heat, it can oxidize and create rust-colored stains.
- Non-Stainless Trowel Use: If a non-stainless steel trowel was used during the stucco application, small amounts of steel could have been embedded in the surface. Over time, these particles oxidize and create rust spots. However, this is unlikely in this case, as a rusty trowel would typically leave smaller, more evenly distributed stain spots across the surface, which doesn’t match the pattern seen in your image.
- Sun and Water Exposure: Heavy sun exposure, combined with moisture from rain or humidity, may accelerate chemical reactions within the stucco materials, leading to discoloration and rust-like stains. This combination of factors makes walls more prone to such issues.
Addressing the Cracking
The cracks on the wall, as shown in your photos, are extensive and more than what I would deem normal. Sealing these cracks, which has been done, is a good first step and is what I would recommend at this point.
If the cracks are unsightly and you want them gone, the next best option would be to embed a mesh into the surface, apply a base coat over the cracks, and then finish it off with a new finish coat of stucco. This approach avoids removing the stucco entirely, while still addressing the visible cracking and providing a fresh, renewed surface.
The cracking you mentioned could be due to thermal expansion and contraction, a base coat that had too much water in it, a base coat that was not properly mixed with the correct ratio of ingredients or lot of movement in the area, it's hard to say.
They are there now and an embedded mesh, base coat and finish coat would be strongly recommended if I were looking at the job myself to protect the wall from future moisture intrusion. This would be after checking for any existing moisture intrusion first, of course.
Solutions to the Rust Spots and Cracking
Here are some possible ways to address the issues:
Topical Solutions (Surface-Level Fix):
- Neutralize the Areas: Remove the finish and base coat in the stained areas and then patch those areas. This would be a good remedy to try to remove specific staining without extensive repairs. There is no guarantee that the stains would not reapper though.
More Extensive Repairs:
- Skim Coat: If the rust spots and cracks are widespread but not deep, a new skim coat of stucco can be applied. Ensure the new coat is properly mixed and applied using stainless steel tools to avoid introducing new issues.
- Full Wall Redo: If the rust spots are deeply embedded and pervasive, or if the cracking indicates structural issues, the entire wall may need to be redone. This would involve removing the existing stucco and reapplying a completely new system.
Prevention for Future Applications
To prevent this issue from occurring again:
- Use high-quality, clean sand and materials that are free of impurities like lignite. Washed masonry sand is the best option and widely available.
- Ensure tools used during application are stainless steel.
Based on your description and the photos, a topical solution like a rust neutralizer and a stain-blocking paint could work as a temporary fix. However, if the rusty spots and cracks are extensive or worsening, a skim coat or full wall redo may be necessary.
Let me know if you have additional questions, Akhnaten. Good luck!
