- THE MAGAZINE
A few years ago, when you mentioned media blasting to a restoration contractor, the usual response was, "What?" Today, the question most commonly asked is not "What is media blasting?" but "What is the right media blasting method for me?"
The answer is not always black and white. My answer has always been, "Let's discuss the two most popular options, and you choose." To truly answer this question, you must look at the advantages and disadvantages of baking soda and dry ice blasting, paying particular attention to how they fit with the intended application.
First, let's discuss the issue of capital - equipment - costs. Both dry ice and baking soda blasting are based on using large volumes of compressed air to propel particles, or media, at high velocity onto an affected surface, e.g. structural wood with mold growth. This typically means securing a tow-behind diesel compressor capable of at least 185 CFM or 70 horsepower. While the compressors are large indeed, they are readily available at most tool rental centers and, because of the competition in that market, are usually inexpensive compared to their purchase price ($200 to $250 per week to rent vs. $14,000 to purchase).
Most contractors tend to rent the compressor and buy the blaster. So how much does a blaster cost? Prices, for baking soda blasting, range from $3,000 to $18,000. The proper set-up, as we recommend it, will cost around $6,000 to $8,000. For dry ice blasting, prices range from $13,000 to $30,000. The proper set-up, as we recommend it, for dry ice blasting will cost around $14,000 to $16,000.
Now let's consider safety. Some detractors of blasting as a whole may argue that mold spores are "broken" into small particles when blasted, and dispersed into the air. This generally doesn't stop most contractors or certified industrial hygienists from recommending blasting because proper personal protective equipment (e.g. respirator masks with HEPA-level cartridges) and worksite containment allow safe working conditions to be maintained.
The largest safety consideration associated with dry ice blasting is oxygen depletion. Dry ice is simply solid carbon dioxide. When blasted, several pounds of solid carbon dioxide per minute becomes hundreds of cubic feet of gaseous carbon dioxide. If proper precautions are not taken, under certain circumstances - think crawlspaces and attics - the carbon dioxide can displace needed oxygen
While this can be overcome with ventilation equipment and/or oxygen monitors, it must be taken into consideration. OSHA lists oxygen deficiency as the No.1 killer in industrial accidents in the United States. Baking soda blasting, on the other hand, may be dusty, but it does not pose this risk.
Although they have different "finishes," both dry ice and baking soda blasting are effective at removing mold from structural surfaces, and at approximately the same strip rate of five to 10 square feet per minute. So how do operating costs per minute compare? Dry ice blasting typically consumes between 1.5 to 3 pounds of media per minute. Given a market average of $0.30 per pound for dry ice, this equals about $0.45 to $0.90 per minute. Baking soda blasting typically consumes about 1 to 1.5 pounds of media per minute. Given a market average of $0.45 per pound for quality baking soda, this equals about $0.45 to $0.60 per minute.
So far the costs appear pretty similar, but let's consider the entire picture. Dry ice is a "just-in-time" product, with little (two to three days) shelf life. It must be ordered for each job as needed, and only when it is needed. Most contractors order 25 percent to 30 percent more media than is needed to do a job in order to not run short before the job is done. Leftover dry ice, as it cannot be stored, is then disposed of. If a job is postponed for more than a day or two, any dry ice on hand is typically too degraded to be used, and new supplies must be ordered.
Baking soda is typically purchased by the pallet and, with proper packaging and flow agents, should have a shelf life of a year or more. When ordering baking soda, if you order a reasonable quantity and keep it dry, it should last for several jobs.
Another cost that must be considered is the logistics, or transportation and storage, of the two media. Dry ice must be ordered for each and every job, and cannot be stored. Dry ice is typically packaged in large insulated totes weighing from 200 to 800 pounds each. A forklift comes in very handy at the receiving site, and a truck or van with a lift-gate is usually required at the jobsite if you want the media within reach of the blast machine. Furthermore, the dry-ice totes are the property of the media manufacturer, so the contractor is responsible for loss or damage to the totes (as well as the return freight charges).
Baking soda is typically packaged in 50-pound bags, with around 2,500 pounds per pallet. Again a forklift, or lift-gate delivery service, is handy for receiving this material; however, the 50-pound bags can be loaded individually onto the trucks or vans for handling at the jobsite. The issues associated with large returnable totes do not apply here.
But what about the end results? Dry ice blasting particles (unless the contractor is using a more sophisticated and expensive ice "shaver" model) are larger than baking soda particles. This difference has several implications: first, the dry ice particles - commonly referred to as "rice pellets" - hit the surface and typically leave "dents," or a dimpled look, on softer surfaces like structural wood. Baking soda's smaller particles - commonly compared to table salt in appearance - leave a smoother, like-new appearance on soft surfaces. Granted, this is structural wood we're talking about here, and appearances are not the overriding concern, but many people (including hygienists, home inspectors and homeowners) object to a "roughened" or "damaged" appearance. This can also be an indicator that some type of dramatic restoration has occurred in a structure, as with the sometimes-objectionable application of pigmented encapsulants.
The number of particles striking the surface is dramatically different when comparing the two media. Dry-ice pellets may contain several thousand particles per pound, whereas baking soda contains several million. Why is this important? It has to do with coverage, and the ability of a small particle to get into nooks and crevices. The smaller particle simply gives better coverage with less damage.
To fully evaluate the "results" of the applications, this discussion would not be complete without recognizing the main advantage of dry ice as a blast medium. Many contractors get the impression that dry ice disappears and that there is no clean up required. But is this really the case? Some projects, such as outdoor blasting, and a few indoor applications such as a partially constructed building (e.g. no windows, doors, and basically open to the outdoors), simply require no cleaning up. When you blast mold growth, or soot and charring off the surface, they are not really gone: the mold spores, soot and charred material, as well as wood fiber and other debris, are still in the area and on the surfaces. Mold remediation requires more in-depth cleanup to eliminate future re-growth and achieve true removal of the offensive material and liability. Smoke and fire damage with dry ice requires the removal of all of the soot and debris for odor removal. Here, baking soda offers something that dry ice does not: baking soda neutralizes odors, both acidic and alkaline.
Just removing the mold growth or soot from the surface is simply not enough. I strongly recommend the same cleaning procedure for any blasting technique. This procedure is best described as a "HEPA sandwich": High Efficiency Particulate Air (HEPA) vacuuming, followed by damp wiping, followed by more HEPA vacuuming, followed again by damp wiping. The only real difference in cleaning procedures between the two media is the amount of material to be swept up before the HEPA sandwich is applied.
Now let's consider the blast equipment. Dry-ice blasting hoses are typically limited to between 40 and 50 feet in length. Going longer usually results in degraded ice at the nozzle, and possible freeze-up in the hose.
Most baking-soda blasters are supplied with a minimum of 50 feet of blast hose, and most units will support up to 100 feet with little effect on the performance. This may not be a factor in many jobs, but remember, the blaster may have to be brought inside containment. If your containment area is an attic or crawlspace, this may be easier said than done. And if your media is still in the truck due to the inability to lift it down, you may be stuck running back and forth with buckets to keep the machine fed (this may not be a big issue with dry ice, because many jobs where dry ice is being used require an additional person outside of containment anyway to monitor oxygen levels on the inside).
I know that this is a lot of analyzing for a topic that, on the surface, appears very simple and something of a fringe process. But almost every contractor that has contacted me in the last two years has asked, "Which media blasting method is right for me?" Analysis of the facts will lead you to the correct process. Consider the options and the applications, and then relax: your job just got a lot easier and more effective.