General sandblasting notes

[BTAZ]

Just finished sandblasting and priming the fuselage and other steel parts.

Some notes:

Use high flow air connectors. I used Milton "V style". Without them, when sandblasting starts, the 80 PSI at the regulator dropped to below 60 at the tank. With them there was hardly any pressure drop. As a side benefit, when I put them on "high air use" tools(like air drills, cutoff tools, sanders, etc.) it made them work much better as well. The female side accepts the Milton V male as well as the typical I/M male(and most other) connectors.

80 PSI at the Harbor Freight "tank type" sandblaster worked fine. My 5 hp compressor was able to keep up but I "T'd in" a second one to take some of the load.

To sandblast small parts in my cabinet, I put them in a couple of the Harbor Freight "Freebie" magnetic parts tray. Worked great for parts smaller then a finger.

I used the "fine/extra fine" coal slag available from Tractor Supply. Used 10 bags, recycling about two thirds off the ground each fill. Filtered the reclaimed material through a window screen back into the tank and worked just fine.

Sandblasting in Phoenix in the Summertime is unpleasant, but the good news is it is so dry that parts don't "flash rust". For a test, I sandblasted some spare tubing before I left for Oshkish and it still had the "freshly sandblasted" silver sheen when I came back a week later.

However, it is tough to not sweat on the project while blasting.

I started out wearing heavy vinyl gloves to avoid leaving finger prints/oils but they would fill with sweat and then spring a leak. Changed over to some well used Tig gloves and all was fine. Used sweatbands on wrists/forehead.

Used one complete 1qt kit of the Stits primer. Decided to use Stits as I still haven't decided on the fabric system and their primer should work fine for any of them whereas the Stewart's might be lifted with the MEK used for Stits. I was surprised at how well it covered and was glad I didn't purchase a full gallon.

Acetone worked fine for cleaning. The primer, even when not set, laughs at mineral spirits.

Used an airbrush (search for a "Critter air-powered spray gun") but mine was a bit smaller(though still not a true airbrush is closer to a "Badger Model 250MT touch-up mini spray gun") and of unknown origins. Used an airbrush compressor and had minimal over spray.

No matter how many times you go over things looking for missed spots, hand the spray gun to someone else and let them go over the fuselage as well. Also a good idea for the blasting process as well.

On to covering.

[Bdflies]

A few years ago, I got a good deal on a really nice blast cabinet. Said cabinet is in my shop (air conditioned shop). Because of the climate controlled environment, blasting small stuff is pretty much at will, anytime. I get the feeling that you're talking about a bigger, outdoor project, huh? I won't do that till November. My hat's off to you, if you're blasting outside in August!

Bill

[whee]

Great post! I've been reading about media blasting in preparation for blasting and painting my fuselage.

I'm curious what everyone's thoughts are on blasting with sand. I didn't know it till I started reading but sounds like blasting with sand it pretty hazardous. OHSA requires the use of a supplied air respirator when blasting with sand. Silicosis is the condition you risk when blasting without the proper PPE. According to the CDC Silicosis and Blacklung are the two primary lung diseases found in coal miners. Also, according to the dose rates I could find it appears that the time required to blast a fuselage is long enough to make you pretty sick unless you are properly protected.

I'm thinking I'll try something else that doesn't have free silicates so I won't have to use supplied air. Maybe walnut shells?

[LukeS]

Whee,
I spent years using a giant 2" hose sand blaster and have no silicosis concerns because I used an over-pressure helmet. An over-pressure helmet is really simple to fabricate with a second regulator off of your paint compressor or other existing compressor and a couple of NIOSH mask filters to clean the compressor airflow entering the helmet. The airflow keeps you cool while you're blasting and, keeps the dust out. Regardless of what media you choose, an over-pressure system beats sucking air through a HEPA mask. Remember to put the helmet on before filling the blaster, as this also is a prime source of dust exposure. Walnut dust will also be super not good for you. Not just for your lungs, but also your eyes and skin. Walnut hulls will also not give the surface prep that sand will. The walnuts will leave a really smooth surface that paint is less apt to stick to than a rougher sand blasted surface. I plan to build an over-pressure helmet system that copies the one I used to use as a metal fabricator using an old full face motorcycle helmet. The relatively small gap around the neck should require fairly little airflow to keep the bad stuff out. You can also use the same system while painting to keep from breathing harmful vapors. A sniff test is the best way to test the system. With the helmet on, open a can of something really stinky. If you can smell it (or anything for that matter), you need more airflow. If you can't smell it, you know the over-pressure system is working. I should also mention that I'm a board certified medical-surgical nurse, and respiratory disease is my bread and butter.

[BTAZ]

When I was younger I used sand and a dust mask and now know that was incredibly stupid.

This time I used a harbor freight hood with positive fed air from a remotely located shop vac.

I wore a dust mask under the hood for some protection when the hood was momentarily lifted as needed during pauses and such.

The research I did recommended the coal slag and it worked great. Much less dust as it doesn't seem to break down. Perhaps using the lower pressure helped as well.

You want an abrasive that leaves a sharp edged finish behind for the primer to grab. That rules out glass beads and the like.

Another recommendation is to remove all labels and tape and clean off the adhesives before starting. I made my fuselage from a fish mouthed tubing kit and the tubes were labeled and had clear packing tape on it. Blasting those off took excessive abrasive and time so I stopped and cleaned as described.

[jaredyates]

When it was time for the fuselage, I rented a 120cfm tow-behind compressor and pressure pot from the local tool place. It worked spectacularly and the cost was worth the time it saved in the suit. I also used about a quart of paint on the fuselage, parts that I painted, though much of it probably ended up in overspray. To put that in perspective, I think I also used a quart to prime both wings.

[nichzimmerman]

This discussion has been extremely helpful! I sandblasted and primed my 4 place fuselage yesterday and just wanted to add another data point.

The job was way more than I bargained for, but was worthwhile as all of the quotes I got from local shops were north of $1000. I started sand blasting at 1pm, finished at 10:30pm, and finished through 3 coats of EP-420 by 6:30am (I had to go to work!). Those three coats used up a 1 qt kit of primer, but I had lots of overspray from my HF gun. I will do a fourth coat when time permits. Admittedly I was very slow, but there were other unforeseen tasks like reconfiguring air compressors and finishing some questionable welds revealed by sandblasting. Murphy’s law and all…

Compressors: I used three, with the largest being an old 5 HP craftsman oil-free unit. I thought two might work, but I wanted a contingency in case one failed, and one did. The two compressors within earshot were running the whole day except when I stopped to fill up with sand. I joined them in a home made manifold, and from there used 3/8” air hose and connections to the sand blaster and didn’t have any air supply problems.

Sandblaster: It wasn’t the harbor freight brand, but I swear in came from the same Chinese factory with different paint. It gave me plenty of problems, and probably added two hours to the job. I tried 3/32” tips, but they clogged too easily so I switched to 1/8” and went through four of them. If the hole got too big, the compressors had a harder time keeping up. I occasionally got spurts of liquid coming out of the nozzle, which baffled me until I realized my water trap was full and one of my compressors was probably leaking oil into the system.

Sand: I went through 15 bags of fine/extra fine sand from Tractor supply. I ended up shoveling about 100 lbs off the ground and filtering it back into the tank, which worked well. I wasted a lot because I had to remove the malfunctioning off valve from the sandblaster handle after sand started coming through the side of it.

Safety: I used a charcoal respirator, cheap goggles, and leather welding gloves from HF. I also wrapped an old shirt around my head for comfort. I had 3 pairs of goggles, and I used them all because the sand would scratch the lenses after a couple of hours. They kept some of the sand out of my eyes.

A rep from PolyFiber recommended that I just blow off the fuselage with compressed air instead of wiping it. I tried wiping a spot before and after blowing it and it was very clean. The fuselage was in a well-balanced free-spinning rotisserie, which I highly recommend. The most important lesson I learned through the process is to have a systematic approach to both the blasting and painting. There are so many tubes and fittings, all of which need to be attacked from three or four sides. After spraying in a disorganized pattern for a while, I went back to the tail post and started going through the fuselage one tube at a time, spraying a coat on each one from four angles before moving to the next.

Overall, I’m glad for the experience and the money I saved, though I may buy a blast cabinet for doing all the smaller parts. And this means I'm almost done with my project....right?

[Mark Moyle]

Garnet 60-80 mesh works well......and is reusable. The fun is in separating the dust from the sand.... Kitchen strainer and a fan works well.....kind of like separating Alaskan tundra black berries in the wind.


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[patrickh99]

If you build an over-pressure hood, make sure you use an oil-free source to supply it. Piston air compressors will add an oil mist to the air which you do not want to breathe, and most respirators will not remove. A vacuum cleaner output would work well: plenty of volume, low pressure, no oil.

[fairchild]

just thought of this---- How about cannibalizing a used CPAP machine (the compressor part)
Have to find a LONG hose---- they make those hoses for the painting mask systems- there must be a source for that hose from a roll.....
not sure what mask- maybe a 3-m full face job ?

[Mark Moyle]

Before I bought the hobby air system....I used a porter cable 2 hp oil less piston compressor and a non-rebreather oxygen mask..... and a rivet gun air valve to throttle the air to the mask... the oxygen mask is similar to the mask an airline stewardess demonstrates before each departure. They can be had at a medical supply store for a few bucks.


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