To blast or not .. and then what. Professional advice sought

[jaws4518]

I saw this discussion pop-up again in my inbox this week. Anyway, this reminds me of everyone's opinion of how to get rid of prickly pear cactus out here in west Texas. You hear a bunch of wise tales and untruths about how you get the job done. It's easy, rake and pile it. It's like raking underbrush. There are different ways of piling and raking to be efficient at it. It all depends of the coverage and how much you have per acre. Anyway, Cactus does not like to be piled. It rots very fast and turns to mulch. Okay, so how does this apply to the art of prepping a new surface? Well, it all depends on how good you want the result to be... The answer to the method is pretty simple. Blast and scale clean! Use the HF blasting cabinet for small parts & bolts. Cut out bad metal and mig weld new structure in its place. Forget bondo gel or other fillers for metal rot. Let your scaled and sand blasted surfaces rust naturally with some good old nitrogen rich rain. A week or so before painting, soak spray the parts and body parts down with OSPHO which will oxidize the natural rust. Use Loctite "Extend" on certain things but not every thing. Extend has "body" to the liquid, and dries like a plastic coating. Too expensive for large areas or things. OSPHO or GEM is putting on muratic acid. It's thin, and it prepares the metal for priming. They say you can use it as a primer, but I put down primer over it.

Blasting does not always work, especially on thick paint. You must scale!!!! Forget the paint removers. Those are a mess and more expensive to use than any other method. I have never seen panels warp from sand blasting. If you try to drill a hole then it will probably warp after a full tank of sand. You must scale the hard stuff. Have your bench grinder near by to keep a flat cutting edge on the end of those needles. When the edge rounds off it is time to resurface. I have never ruined anything with the needle scalier. I'm not going to use a needle scalier on something that I'm worried about being perfect. The scaling dings "if any" are a better bonding surface for primer to begin with. More on paint next....

 

[frank8003]

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[Karl kostman]

If I were in your shoes and you dont want this truck to be the new most beautiful Deuce in the country is replace the doors, I would talk to Deuceman51 on this site. I would pull the fenders off the truck and get them fixed, dents, rust etc if you can do this yourself all the better.

I would get all the body work done on the truck that you feel is needed then I would pressure wash everything off very good and run over the truck with a good Dual action sander (DA) there is no need to remove the paint because it makes an extremely good base to put your new paint onto and removing all that paint is going to be a needless pain in the butt!
If the bed needs work I would pull the bed off the truck then attend to the frame touch up and work on the bed I would then paint the truck and the bed separately you will get a much better job done to the truck with the bed off it and this will allow the painter to do a much better job on the frame! Good luck its a bit of work and time but nothing complicated.
Karl

 

[jaws4518]

Yeah, I concur on that. If the existing paint is solid then feather it out and paint over it. My situation with this 1970 Kaiser Jeep XM818 was a extreme case of layers of paint. All of the panel gasket rubber is rotten. The paint has caused binding on hood, doors, and anything that adjusts or moves.
Since the tractor was in great shape I decided to take it apart and do things right. There was no midway entry point. The old layers of paint were causing all kinds of clearance and rust problems. I was faced with keeping it as a junker, or restore it like new.

I'm still working on it and I hope to have it completed this fall. No hurry, just whenever... Anyway, get a needle scalier if you do not have one. It will take the paint off where blasting becomes impossible. I power wash also, but that has its limitations too! So, the answer to the "method" is everything which has been discussed. There is no single method.

 

[tennmogger]

I saw this discussion pop-up again in my inbox this week. Anyway, this reminds me of everyone's opinion of how to get rid of prickly pear cactus out here in west Texas. You hear a bunch of wise tales and untruths about how you get the job done. It's easy, rake and pile it. It's like raking underbrush. There are different ways of piling and raking to be efficient at it. It all depends of the coverage and how much you have per acre. Anyway, Cactus does not like to be piled. It rots very fast and turns to mulch. Okay, so how does this apply to the art of prepping a new surface? Well, it all depends on how good you want the result to be... The answer to the method is pretty simple. Blast and scale clean! Use the HF blasting cabinet for small parts & bolts. Cut out bad metal and mig weld new structure in its place. Forget bondo gel or other fillers for metal rot. Let your scaled and sand blasted surfaces rust naturally with some good old nitrogen rich rain. A week or so before painting, soak spray the parts and body parts down with OSPHO which will oxidize the natural rust. Use Loctite "Extend" on certain things but not every thing. Extend has "body" to the liquid, and dries like a plastic coating. Too expensive for large areas or things. OSPHO or GEM is putting on muratic acid. It's thin, and it prepares the metal for priming. They say you can use it as a primer, but I put down primer over it.

Blasting does not always work, especially on thick paint. You must scale!!!! Forget the paint removers. Those are a mess and more expensive to use than any other method. I have never seen panels warp from sand blasting. If you try to drill a hole then it will probably warp after a full tank of sand. You must scale the hard stuff. Have your bench grinder near by to keep a flat cutting edge on the end of those needles. When the edge rounds off it is time to resurface. I have never ruined anything with the needle scalier. I'm not going to use a needle scalier on something that I'm worried about being perfect. The scaling dings "if any" are a better bonding surface for primer to begin with. More on paint next....

So, search really works! This post by Jaws4518 really answered my question. Yesterday was a big sand blasting day here on the farm. I had a mobile media blaster come in and completely strip a 1984 Radio box off a 404 Unimog. We also blasted the roof and rust trouble spots on a second radio box. Big job but imagine doing that by hand.

Then it rained. Unpredicted of course, and it is going to rain more today. Then I read on here "let it rust in the rain", Ospho it, prime, top coat (summarized). So all was not lost when it rained!!! I have time to work now.

Thanks for the guidance.

 

[NDT]

That has to be the worst advice I have ever heard, to purposely let a freshly blasted white metal surface get rained on. In my world, rained on blasted surfaces get re-blasted so the expensive paint is adhering to the anchor profile, not crappy ospho.

 

[tennmogger]

Maybe you missed the point or I failed to pass the idea that It Already Got Rained On. Not purposely left out in the rain. Rain is not a treatment! That would be dumb.

What advice would you give, other than calling the blaster back (which isn't going to happen).

 

[NDT]

My comment is directed to post # 21. I have no advice for you since you say reblasting is not an option.

 

[tennmogger]

I stand corrected, I missed that in the early post. I see wire brushing in my future.

 

[87cr250r]

No need to wire brush. Wipe it down with phosphoric acid.

Some paints will tolerate some flash rusting. Hydroblasting is gaining popularity for industrial applications for a variety of reasons. There are corrosion inhibitors that can be added to the water to prevent flash rusting but most paint manufacturers prefer the flash rust for adhesion over inhibitors.

The issue is adhesion failure due to hydration. Paint adheres to materials by an exchange of electrons. The exchange is very strong between bare metal and paint. Oxides of metals hold on to their own electrons and don't share so well. The initial adhesion may be acceptable but as the paint is exposed to water, the water has a stronger affinity for the electrons in the oxides and forms hydrates. As this happens the the bond with the paint is lost and it blisters or peels off.

Hydration is a likely cause of failure of that Titan submarine that imploded. They didn't etch the surface of the titanium end caps before bonding. Titanium and aluminum form surface oxides readily in air without water. Steel is more forgiving.

Make sure to use a zinc rich primer anywhere you go bare metal.

 

[98G]

I stand corrected, I missed that in the early post. I see wire brushing in my future.

I've got a bare steel welding table that sits outside in the weather in KS. It's rusty of course.

About 3 years ago I spent about a minute with a powered wire brush knocking the worst of the rust off a small patch of it and then shot it with that rustoleum rust converter with no further prep.

It remains flat black.

I've been using that rust converter as part of my prep for refinishing rusty steel ever since.

 

[biscuitwhistler37]

I've got a bare steel welding table that sits outside in the weather in KS. It's rusty of course.

About 3 years ago I spent about a minute with a powered wire brush knocking the worst of the rust off a small patch of it and then shot it with that rustoleum rust converter with no further prep.

It remains flat black.

I've been using that rust converter as part of my prep for refinishing rusty steel ever since.

I wondered about that stuff forever, just waaay to skeptical to try it . Definitely going to pick some up now knowing it works.

 

[jaws4518]

That has to be the worst advice I have ever heard, to purposely let a freshly blasted white metal surface get rained on. In my world, rained on blasted surfaces get re-blasted so the expensive paint is adhering to the anchor profile, not crappy ospho.

Ospho/Phospho prep is still the best solution for preping metal and killing rust. Loctite Extend is too! I have been using both for years. If they were so crappy they wouldn't be so popular. They are designed to chemically react to rust. They react nicely to fresh rust residue. The product directions explain ideal surface conditions. Shiny or clean steel is not recommended. I prime clean steel with a metal primer. I will be posting some restoration projects where they were used. So my original point was let it rust in the rain, spray or brush on Phospho, high pressure wash, then prime.

 

[G744]

Most of the 50's vintage tacticals were primed with red oxide primer at the factories. The real red stuff, not the modern brownish color. You can see it occasionally under the green (or blue or grey) topcoat on a rig that hasn't been apart for a long time.

It binds like crazy to clean steel, and will tolerate a bit of very light surface rust if you get short on time or something like that.

I've had an M37 frame done in just that, sitting around for 30 some-odd years and it still looks fine. I use it on all my tacticals when it is time for a paint job.

Not that modern tech hasn't given us some great coatings now, but that old school stuff was formulated to do the job right, and easier to deal with by far.

BTW, the OP is in Eastern Europe, don't think old Harbor Freight sells there...

 

[87cr250r]

It is best practice to paint IMMEDIATELY after blasting. Metal in air oxidizes, the layer can be microscopically thin so you don't see it. When you apply paint it adheres to either the metal or the oxides. On an atomic level, adhesion is a sharing of electrons. Paint sticks to metal and paint sticks to rust, the problem occurs when you expose everything to water. Water has a higher affinity for the electrons in the oxides than the paint does. Over time, the water hogs all of the electrons and turns the oxide into a hydrate. This causes the bond between the paint and the oxide to fail. This is especially problematic for aluminum or titanium but is also an issue for steel. Modern paint systems use silanes to prevent hydration.

No paint manufacturer recommends allowing the surface to bloom. Some paint manufacturers will advertise their paint as tolerant.

 

[98G]

Most of the 50's vintage tacticals were primed with red oxide primer at the factories. The real red stuff, not the modern brownish color. You can see it occasionally under the green (or blue or grey) topcoat on a rig that hasn't been apart for a long time.

It binds like crazy to clean steel, and will tolerate a bit of very light surface rust if you get short on time or something like that.

I've had an M37 frame done in just that, sitting around for 30 some-odd years and it still looks fine. I use it on all my tacticals when it is time for a paint job.

Not that modern tech hasn't given us some great coatings now, but that old school stuff was formulated to do the job right, and easier to deal with by far.

BTW, the OP is in Eastern Europe, don't think old Harbor Freight sells there...

Climate makes a huge difference. I'd trade your climate with bare steel against KS or GA + any coating you'd care to use.

I've experienced both.

 

[87cr250r]

Most paint manufacturers have a "red" primer available. This refers to an alkyd based primer. They work but they don't work well. There is nothing about an alkyd that makes it superior to an epoxy.