Not Our First Rodeo
Setting up to clean the Alfatross was not our first experience with soda blasting. Many years ago we figured out how to clean pewter plates recovered from a ship that sank in 1686 using abrasive blasting. Pewter is a very soft metal composed mainly of zinc. There were fine patterns etched on the plates that had to be preserved, so we approached the task with caution. We tried using fine pumice, then cornstarch, and even corn meal before we settled on wheat flour as the best medium to use. Bread flour would not be the first thing that pops into your mind when you are looking for an abrasive substance, but in this case it was perfect.
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| Cleaning pewter plates that had been underwater for more than 400 years using wheat flour. |
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| After cleaning the plates even fine details such as this design etched into the surface were preserved. |
Not for Sissies
Like getting old, soda blasting is not for sissies! It looks so easy, so simple in the Eastwood catalog: "Soda removes paint without damaging or warping metal, is environmentally friendly and strips without chemicals." Fact is, soda blasting is a great tool, it's just that there is a lot more to it than meets the eye. And we all know how men love to buy and try new tools . . . .
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| Tool envy: Look guys! New tools you can't live without! |
So why all the hype about blasting with sodium bicarbonate (NaHCO3)? In the first place, it is very gentle. Soda crystals have a hardness of about 2.4 on the Mohs Hardness Scale. That's the same as the average human fingernail: hard enough to remove paint, but not hard enough to damage the underlying metal--or even rust! Soda crystals "explode" upon impact, turning into even finer particles that just seem to disappear. It dissolves in water and is safe--even beneficial--to wash into sewer systems (once contaminants have been removed).
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| The Alfatross gets blasted. |
The descriptions you read in the soda blastng sales brochures make it seem pretty simple. OK, it isn't rocket science, but there is a lot more to it than you might think. In addition to the blaster, soda, and rotisserie, you're going to need a few other things:
- High volume, low pressure compressor
- 1/2" diameter supply hose from compressor to blaster
- 3/8" diameter air gun hose to blow off dust
- Large funnel to recharge blaster reservoir
- Ground tarps to catch debris for faster cleanup
- Weights to hold tarps down
- Wrenches for various parts of the blaster
- Many 5-gal buckets
- Sifter with 1/16" mesh
- Scoop for transferring soda
- Dust pan and brush
- Push broom
- Sun shade tarp
- Vacuum cleaner
- Goggles
- Respirator
- Head protection
- Ear plugs
- Jump suit
- Keffiyeh
- Heavy rubber gauntlets
- Sacrificial boots
- Cooperative weather
- Thirst quenchers
- Advil
- Long, hot shower
The actual experience of soda blasting is a lot like working on a shipwreck excavation under water. By the time you're suited up, masked, and ear-plugged the sensory deprivation is much like being in a wetsuit underwater. All you can hear is yourself breathing. You've even got an umbilical hose connecting you to a compressor! Open the valve on the soda blaster hose and visibility goes to zero for a few seconds until the water--I mean air--clears enough to see what you're doing. After an hour or two of this you're more than ready for a "surface interval" so you can peel out of all that equipment and hear, see, and breathe again!
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| Shipwreck excavation underwater is surprisingly similar to soda blasting, |
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| As soon as the work starts, visibility drops to zero. |
To complete the analogy, in both cases you're uncovering something important albeit with slightly different arrangements of compressors, hoses, and life-support systems.
But There's a Catch . . . .
Unlike sand, which can damage lung tissue, sodium bicarbonate is as harmless as a useful substance can be. Also unlike sand, soda doesn't recycle well, so you need a lot of it! About the only down side is the cost. The initial cost of about one dollar per pound almost doubles when you factor in shipping. Cleanup is easy, but even though the soda is harmless the paint and debris removed from the car might not be, so it has to be disposed of properly. Soda is good at removing grease, too, through the process of saponification (grease + NaHCO3 = soap). Its chemical composition makes it amphoteric (a good pH buffer), meaning that it has the characteristics of both an acid and a base. As such, it inhibits flash rust on newly exposed surfaces. Finally, because it is water soluble there is little danger of abrasive entrapment in moving parts.All this is good news for the Alfatross, but what's the catch? Stripping the Alfatross naked of its paint and other coatings leaves it vulnerable to oxidation (corrosion). Fortunately, Northern New Mexico is in a protracted drought and relative humidity this time of year is in the single digits. Still, even though soda leaves a film that inhibits rust, it won't last forever. Before the Alfatross is ready for paint we will have to pressure-wash it to remove all traces of the soda used to clean it. One company recommends adding a product called Hold Tight 102 to the pressure-wash mixture for optimum results. It seems to be some type of surfactant (a chemical that makes water "wetter"). So we can add "pressure washer" and "Hold Tight 102" to the list of equipment and supplies needed to do a proper job of soda blasting.
But before we get to the paint stage we still have to make repairs to the Alfatross' steel frame and aluminum body. As the soda blasting chapter comes to a close, the more expensive, time consuming, and expertise-intensive body work and paint chapters lie ahead . . . .
