Water blasting for paint removal. I've heard it mentioned here on more than one occasion but never heard the pro's or con's or who does it. How do you keep the metal from rusting after the blasting is one question we have. The other is there any one around the Ohio area that does it?

irss@eriecoast.com

I have seen water blasting used for paint removal on U.S. Navy ships, and in all cases where some type of primer wasn't applied almost immediately, the result was a thin layer of rust that had to be sanded off before it could be properly preserved.

Boyd


bowens@rypn.org

Some years ago, the RR I worked for leased two Alcos to a lumber importer to run his own special intermodal train, in what had to be one of the most ridiculous and stupid piggyback schemes you could imagine. Aside from that, however, the engines were sandblasted by an outside contractor (which we union workers had a less euphonious term for) who used a wet-blast technique with Black Beauty abrasive and a pressure washer. While the paint came off, the result, as you can imagine, was an instant coating of rust. After the blasting, he applied an acid of some sort (perhaps phosphoric) which took most of the brown rust off. The units were then primed with self-etching primer and painted with Centauri. The paint seemed to hold pretty well when I last saw them, and may still be if they are still extant. However, the idea of causing rust while you're removing it doesn't make much sense to me. Given a choice, I'd blast with air.

> I have seen water blasting used for paint
> removal on U.S. Navy ships, and in all cases
> where some type of primer wasn't applied
> almost immediately, the result was a thin
> layer of rust that had to be sanded off
> before it could be properly preserved.

> Boyd


ryarger@rypn.org

> Some years ago, the RR I worked for leased
> two Alcos to a lumber importer to run his
> own special intermodal train, in what had to
> be one of the most ridiculous and stupid
> piggyback schemes you could imagine. Aside
> from that, however, the engines were
> sandblasted by an outside contractor (which
> we union workers had a less euphonious term
> for) who used a wet-blast technique with
> Black Beauty abrasive and a pressure washer.
> While the paint came off, the result, as you
> can imagine, was an instant coating of rust.
> After the blasting, he applied an acid of
> some sort (perhaps phosphoric) which took
> most of the brown rust off. The units were
> then primed with self-etching primer and
> painted with Centauri. The paint seemed to
> hold pretty well when I last saw them, and
> may still be if they are still extant.
> However, the idea of causing rust while
> you're removing it doesn't make much sense
> to me. Given a choice, I'd blast with air.

During WW2 a paint foreman on the UP told a group
of us that they had solved the problem of getting
paint to hold on tank cars. He said they sand blasted them and then sprayed them with a fine mist of water. When they got a fine thin coat of red rust on they they painted right over the rust.
Apparently the rust gave the paint something to hold to and the coatings held.

The late lamented Mt. Vernon Car Manufacturing Co, shot blasted their finished cars then immediately painted them. The RR I worked for had bought some of their box cars and several years
later when we ran a repair program on them we
found that even after sand blasting the cars, red
originally, still had a red cast to them.


rrfanjim@mvn.net

We water blasted the E-8's and the Warrior Ridge. It is quicker, less expensive than sand, infintely cleaner and not as distructive and finally so easy to clean-up afer.

The paint and finish on the equipment we use is just as good as the day it was applied!

Check out the process on the PRRTHS WEB site, under Philadelphia Chapter, Restorations.



v-scarpitti@att.net

You might find a contractor through the Water Jet Technology Association. They have a web site at www.wjta.org (link below) and can also be reached at:

917 Locust, Suite 1100
St. Louis, MO 63101-1419
Telephone: (314) 241-1445

A Google search for "water jet" will also reveal various contractors offering this technology.

I think earlier responses in this thread have already addressed your other questions. I would only add that you'd also better apply primer very soon after sandblasting or any technique that leaves bare metal exposed to our damp midwestern air.


Water Jet Technology Association
pnichol6@prodigy.net

Take a look at this link. We have used this method before and it works. Not this company though

http://www.polarblast.com/

> Some years ago, the RR I worked for leased
> two Alcos to a lumber importer to run his
> own special intermodal train, in what had to
> be one of the most ridiculous and stupid
> piggyback schemes you could imagine. Aside
> from that, however, the engines were
> sandblasted by an outside contractor (which
> we union workers had a less euphonious term
> for) who used a wet-blast technique with
> Black Beauty abrasive and a pressure washer.
> While the paint came off, the result, as you
> can imagine, was an instant coating of rust.
> After the blasting, he applied an acid of
> some sort (perhaps phosphoric) which took
> most of the brown rust off. The units were
> then primed with self-etching primer and
> painted with Centauri. The paint seemed to
> hold pretty well when I last saw them, and
> may still be if they are still extant.
> However, the idea of causing rust while
> you're removing it doesn't make much sense
> to me. Given a choice, I'd blast with air.

Re: Water blasting and rust
After removing the paint and making needed repairs to the metal you will have some surface rust. you will need to give it a bath of "Rust-mort" this will kill all fine rust and after 24 hrs. is washed off with water. you need to start painting within 24hrs. This product can be found at auto paint stores. Also keep in mind that primer will not seal out water from getting to the metal, you need to add the color coat in a timely fashion
P.S. Self- etching primer is great! however it can be a killer! you must work with a fresh-air breathing system.
Dave Wolven O.E.R.M.

davewolven@msn.com

Like all good things, CO2 blasting has advantages and disadvantages. It isnÂ’t very good at removing rust. It works at very high pressures, which can damage softer surfaces, and may cause OSHA problems. The media, most commonly dry ice "rice" is not readily available, doesnÂ’t keep well, and can be expensive. The system is especially good for cleaning elastic surfaces (think bubble gum off of rubber flooring.) It not only removes the material by abrasion, but also can freeze, and inbrittle the coating. Its greatest advantage comes when removing hazardous coatings like lead, since the media sublimates as you blast, you are only left with the removed material, not a ton of contaminated sand.

Since dry ice is cold, (-210 f) I would be concerned with the effect of the cold on the metal of a pressure vessel.

Randy Hees


http://spcrr.org
hees@ix.netcom.com

Remember, it's CO2, so don't use in a confined space. People go to sleep and never wake up from a gradual asphyxiation.

I'm sure most here understand this, but just wanted to say it.

Don't you mean CO or carbon monoxide? C02 is generally considered a non-toxic gas.

> Don't you mean CO or carbon monoxide? C02 is
> generally considered a non-toxic gas.

While CO2 is considered non-toxic, it does not support life.


lamontdc@adelphia.net

> While CO2 is considered non-toxic, it does
> not support life.

That is correct, it displaces the oxygen. Human beings do not thrive in an inert atmosphere.


nwstaybolt@reachone.com

My two cents....

There are a lot of misunderstandings concerning terminology. One of those terms is "toxic". Most people think that "toxic" means means it will kill you now like cyanide and antifreeze. While this is true, "toxic" is a very general term in that toxicity is a function of dosage and concentration over a given period of time. Believe it or not, water can become toxic. In normal everyday amounts (dosage) it is beneficial to life and health. When a few gallons are forced down at one time, (if possible) the story changes, your blood chemistry is adversely affected and illnes and even death can result. Same thing holds true for asprin, two pills are good, a whole bottle is not. In the same way concentration also plays a roll in toxicity. It is the "strenght" component of the material such as the CO2 being discussed. Carbon Dioxide is a trace substance in the air we breath everyday (we exhale it) as it is what plants and trees consume to make their food. However, sit in a small sealed room with ten of your closest friends or a bucket of sublimating dry ice and it is no longer a trace amount.

The same concept is true for oxygen. Generally it occupies 19-21% of the air we breath. Once that concentration is elevated in an environment such as a pit or an area of a building, the ignition temperatures of the materials in that environment start to drop. That is why you should never blow yourself off with oxygen in the shop. Your clothes are now saturated with oxygen and there is likely oil on them as well which is not a good thing. Any spark or other ignition source and you are on fire until the clothes and/or the oxygen are gone. This is why oxygen regulators say "use no oil" as it make oil burn a lot easier (I have no idea why a regulator would need oil anyway). Most people don't give oxygen a second thought as it is all around us. This also makes it dangerous as it is not respected as being potetially very dangerous. I worked on a project last year involving high pressure hydrogen and oxygen at 3,100 and 3,000 respectively in the same test rig. There are only a few materials that don't burn in pure oxygen. Stanless steel was the chief component of that system and it can ignite from a 100 micron particle flying through the system and striking a surface just right as well as residues. Needless to say system cleanliness was of paramount importance.

Another misunderstood term is "hazardous". While this is different, a subtance can be readily hazardous at ambient conditions or can become hazarous through heating, for example. One of the factors that contributes to a fluid being labeled as such is its flash point. This is the temperature at which the vapors above it ignite, but do not continue to burn. The flashpoint temperature, if memory serves, is around 115-120 F to make some thing hazardous such as a cleaning solvent. This is important to know for handling and using. If you have a low flash point solvent in your RR shop you may want to keep the sparks away and the cover shut for the reasons above.

The auto-ignition temperature of a material is just that, the temperature at which it will ignite on its own and support combution. Kerosene has a relatively low auto-ignition temperature. This is why it helps your Diesel engines to start in the winter when mixed in with the Diesel fuel along with lowering the fuel's pour point.

> Human beings do not thrive in an inert
> atmosphere.

Ever work in a public sector bureaucracy, Nathan?

dave

irondave@bellsouth.net