The Finish Line: All About Rust
August 27, 2008
Rust streaks: It’s surprising how one teeny tiny granule of iron-the size of a pin head-can ruin an entire EIFS façade.
Large rust stain streaks can be created by an almost invisibly small piece of iron, located in the EIFS finish. They can become amazingly big and very noticeable. In the midst of a huge blank EIFS wall, such streaks can really standout, which can result in irate building owners who want you to redo the whole façade. That level of repair is hardly necessary and the following information on rust streaks on EIFS can help you fix the problem and keep the owner calm.
First, you are probably thinking, “Rust is no big deal.” In a sense, this is true, as rust has no effect on the integrity of the wall-it just looks lousy. But rust was once a major issue in the EIFS industry and it occasionally rears its head on jobs nowadays. At one point, many years ago, rust was showing up all over the place. Hundreds of projects were affected. No one knew why-there didn’t seem to be a pattern as to why this was occurring. It took some detective work and cooperation between EIFS producers to find out why this was suddenly occurring. Now, things have calmed down and although rust is hardly common anymore, it does show up on occasion and for various reasons.
What is Iron?
Iron is one of the raw materials of nature, such as oxygen or hydrogen. Steel is made of iron (and carbon and other materials). Both iron and steel can rust. Stainless steel has chromium in it and doesn’t rust anywhere near as easily. Neither does aluminum rust-it has no iron in it at all. Why? Stainless steel and aluminum naturally produce a minute coating on the surface that prevents air and water from getting to the base metal, hence “rusting” never gets a chance to start. This is not to say that these materials are totally unaffected by the environment but it’s more in the form of less detrimental corrosion, than “rust” in the normal sense. Steel and iron do not behave in this manner of corroding in a slow, non-benign way-they rust like mad. Worse yet, the surface that is created by rust on steel or iron sloughs off, re-exposing the base metal to the elements. This re-exposure effect is sometimes referred-to as “scale.”
Once this process starts, the rusting continues until there’s no iron-bearing material left-like a car fender rusting-through. On a building wall, this “rust” is sloughed-off iron-bearing material that flows downward over the surface of the EIFS finish under the force of gravity in rainwater. When the water dries up, the reddish iron that was suspended in the water appears on the surface as a rust stain. Rust stains are usually red but as they age, they can also turn gray or somewhat white. Thus, they can be obvious on both light and dark colored EIFS walls.
Once the rusting starts, it will continue until all the iron bearing source material is used up. This can take months, even for a tiny speck of iron. Eventually, most rust stains turn white-ish and then usually wash away, leaving a clean wall. The problem is that this takes longer than the patience of the building owner (this washing-away process can take years).
Keep in mind that this “rusting” process can occur in stucco or cement or any other wall surface cladding that has iron bearing materials in it.
The Plot Thickens
It’s easy to find the iron source. All you’ve got to do is “get up on the wall”, and follow the rust streak upward, until it stops. The offending iron particle is at the top of the streak. Often the iron particle is smaller than a pin head, yet can produce a rust stain several feet long.
Sometimes, people make the mistake of trying to paint over the streak and the iron particle. This doesn’t work. The types of paints-usually acrylics-that are used with EIFS finishes, are water vapor permeable and the rusting will re-start due to the presence of moisture nearby, despite being covered with paint. When painted-over, moisture can still get to the iron, and it expands (“blooms”) through the paint, and the rusting process begins again.
The key is to dig out the rust particle, and then use a rust stain remover to get rid of the rust streak. Then the affected area is painted over with matching EIFS finish-paint. (A helpful hint: the paint can be EIFS finish-paint, made by taking the matching EIFS finish and pouring it through cheesecloth to produce a brushable “finish” with no aggregate in it.)
Keep in mind that EIFS finishes and even smooth paints at a microscope level have tiny hills and valleys in what appears to the naked eye to be a smooth surface. Water that is carrying microscopic particles of iron can get into these valleys. The EIFS finish, when wet, softens slightly. The iron can thus get embedded into the softened surface, not just sitting on the surface. Again, this can make removing the stain difficult, as the stain is in the finish coating, not on it. This makes removing the rust stain very difficult or impossible at times.
Various commercial products are available that are compatible with EIFS coatings to remove rust stains. Be careful not to use super heavy duty, not-for-EIFS, rust stain removers, as they can bleach the EIFS finish. After cleaning off the stain, flush the wall with a lot of water to get the cleaning materials off the finish.
So How Does The Iron Get There?
Now you’re probably asking, “How did the iron get there in the first place?” There are a couple of ways. Clearly, if someone is welding nearby and an open pail of EIFS finish is present, iron-bearing weld spatter might get into the finish, causing rust streaks. Similarly, filings from metal grinding operations can do the same thing. It’s even possible for the trowel used to apply or texture the finish to cause rust. If the trowel or float is plated plain carbon steel (not stainless steel or plastic or wood), it can contaminate the finish with iron-bearing materials.
However, the real culprit is often the aggregate in the EIFS finish. Here’s why. The term “inclusion” refers to a spot on a mineral particle that has some other material in it. An example might be a garnet (a reddish, semiprecious stone), which is sometimes found as a small jewelry-like crystal on the surface of a big piece of granite. Iron can also be an inclusion on small pieces of stone (like silica sand), and since iron rusts, therein lies the rust problem.
Many mainstream brands of EIFS finishes use silica sand (quartz) as the aggregate. Sand is a natural material and is found in deposits, such as riverbeds. Being a natural material, sand is subject to variations in its composition. One undesirable bit of contamination of the sand is tiny chunks of raw iron that are either loose or are small nodules attached to the side of a sand grain as an inclusion. These iron particles are microscopic and very difficult to remove.
Some EIFS producers use magnets to try to pull these offending particles out of the sand during production of the finish coating. To say the least, this is like looking for a needle in a haystack and the specification for the sand in a proper EIFS finish is measured in parts-per-million of iron. Some EIFS producers rely on high-grade (uncontaminated) sources of sand to help lessen the possibility of getting iron into the products.
Some EIFS producers use materials other than quartz sand as their aggregate. For example, marble can be used, and it can be crushed from large chunks and is relatively less likely to have iron in it. Going one step further, it is possible to use man-made materials as aggregate. This includes industrial byproducts, such as various types of grits that result in combustion processes. These man-made materials can have a constant, iron-free composition and thus are essentially rustproof.
Lots of Rust Spots
If a wall is heavily contaminated with rust streaks, digging out the many culprits-usually many single rust particles-can be a real hassle. You can spend hours moving equipment around just to get to a single rust streak.
A nut picker works well for digging out the iron particle. Some people have tried grinding, using a cordless Dremel tool and carbide burl tip. A big wheel-type grinder makes too much of a mark on the surface of the finish.
After the rust source particle has been removed, the stain can be removed with a rust cleaner, and the affected area painted over.
To remove rust stains, check the offerings of Wind-Lock and Demand Products, both of whom sell cleaners for rust on EIFS, stucco and so on.
If there are a lot of rust streaks, this rust removal process can involve a lot of scaffolding moving, which can be time consuming and expensive. To get around this, I’ve seen brave workers using boatswain’s chairs to get to rust-infested areas. They remove the iron particle, clean the streak, and paint-over the affected area, all in one “drop.”
Other Sources of Rust
There are other sources of rust stains than iron granules in the EIFS aggregates. These include rust-able non-EIFS wall components, such as fasteners and downspout attachment straps.
If not-made-for-EIFS plated carbon steel washers (instead of plastic) are used in EIFS mechanical fasteners, they will tend to rust right at the fastener location-and cause visible discoloration of the wall in that area. The same is true for indoor grade (with minimal protective corrosion plating) drywall screws that are sometimes used with EIFS mechanical fasteners.
Rusting can also occur with non-corrosion-resistant fasteners, especially if they are close to the surface. Bolts and brackets that go through the EIFS to attach surface mounted objects, such as handrails, signage and flag pole holders, also tend to create rust stains.
Some types of climates are more conducive to rust than others. Dry, warm climates are the least rust prone. Hot, humid, salty areas, such as the southeast coast, are the worst. Areas with industrial air pollution can also provoke rust. Rust stains generally do not show up right when the finish is applied, but rear their heads weeks later, after the humidity and rain has had a chance to work on the iron.
A Big Deal-A Bit of History
A decade or so ago the rust issue became a big deal for the EIFS industry almost overnight. The EIFS industry was plagued by reports of buildings suddenly sprouting major rust problems. For a while, no one was sure of the cause.
It turned out that many EIFS producers were obtaining their sand from the same source, and that source had reached an area in the sand deposit (that they were mining) that had a lot of iron in it. Previously, the sand source was iron-free, but no longer.
Once the rust source was identified, the task began of either getting the rust out of the sand-a difficult task-or finding an iron free sand source. With a little intuition, you can now see why many EIFS producers have their plants in the same geographic areas. For instance, “good” sand is found in the southeast and parts of the west, while marble is common in New England and Georgia.
YOU AND RUST AND THE FUTURE
These days, rust rarely shows up, but when it does, it can be a real hassle. Usually rust occurs as individual, isolated streaks, and can be taken care of with little sweat. If the whole wall is peppered with rust stains, the rust may be coming from within the finish.
Will you run into a rust problem on any of your projects? Probably not, but once in a while a single pail of EIFS finish gets contaminated by iron filings or some other one-time source, and a small wall area that is using that pail of finish sprouts “iron measles”, while the rest of the building is fine. Most of the rust you are likely to see is not in the middle of an EIFS wall, but due to some other rusting wall material nearby, such as steel fasteners, steel mounting brackets, railings, or painted steel flashings. Such non-EIFS-based stains on the EIFS surface can be cleaned-off as described above. W&C