Blasting vs. sanding (rust repair)

[jkelly]

Sounds like you guys have done a lot of what I'm planning to do. I have a good bit of rust in my cowl too, mainly around the vent tube near the passenger side. The vent tube has some rot around it so I'm going to drill the spot welds on the piece of sheet metal covering it and remove that, then cut out the bad vent tube metal and replace it. I'll probably spot blast and Ospho what I can't get to with a grinder. Those little siphon feed spot blasters are surprisingly effective. I'm using mine with a 5HP 60gal Quincy.

I feel you on the paying someone else to do it. After doing my own floor pans, frame rails, battery box, and about to be dog legs and cowl vent I'm ready to focus on restoring the interior. Anything but grinding grinding grinding, spot weld drilling, etc. Although, I do enjoy the welding.

Those purple 3M wheels look interesting, I might have to pick some up and test themout.

I'm testing the Ospho on some rusty parts at the moment. I'm on two coats already and tonight will be 48 hours of it sitting there "converting". We'll see. I'm planning to shoot some PPG DPLV (Yay for compliant California paint ) on there and see how it adheres. I've read that epoxy primers are okay to shoot over Ospho, but a self etch primer containing acid will not bond properly. I've read everywhere that at the very least you have to rinse Ospho off with water to neautralize it. Your process sounds better, except you can't always wipe some areas down with W&G remover. It's nuts how the Ospho instructions don't mention anything about rinsing -- just dust off the white powder and paint. I've read about a lot of paint failure using that method.

Initial Ospho application:

After 24 hours:

It looks darker but no white powder like the Ospho folks mention.

After 48 hours:

Not much difference.

Edited October 25, 2017 by jkelly

[Greeko]

From my brief tenure as hobby car restorer I have learned a couple things....

Home DIY Blasting, dipping, rust removal BLOW FAT CHUNKS!!! Messy, dirty, painful and a WASTE of your time...

I enjoying doing it myself.. (pause for horrible joke to set in) but certain things I will send off and happily pay a little more or most likely the SAME up front and have a professional do the blasting/rust removal... Once that is done heck yes I will have fun welding new patches in, skimming etc....

And on that note...I have also learned to SPEND MORE MONEY and get a better vehicle to start on (unless there is a sentimental attachment to the original vehicle).. People have this idea that if they buy the cheapest Vehicle out there it will cost them the least amount of money...IT WONT!!!.Ask me how I know...lol..

Just my rant after finding more awesome rust in a spot I had already gone over ...sigh..Never ends lol

 

 

Edited October 25, 2017 by Greeko

[tamo3]

I totally agree of your opinion. That's the reason I sold my 240z and move onto current 280z.

[seattlejester]

With the right setup you can do decently at home, the problem is it is hard to really invest in something you might do for a very limited time. I gave away my whole setup once I was done with it, probably broke even for the amount of blasting I did. If I sold it probably could have come out on top a bit. So there is indeed some merit in having a professional tackle it.

It really is a matter of how much you value your time, with the factor of reliability of the shop doing the work. If you can find a place that has a proven track record with a set time frame that would be great, but the unfortunate thing you run into is that those time frames can be moved or changed, and sometimes you will find 90-95% completion, something you don't notice until you get home, then have to spend a ridiculous amount of time fixing  or trying to get the last 5-10%.

The last item I had blasted still had caked on grease/dirt. I think the guy just missed it as the piece filled up with blasting media an stuck to it. Innocent mistake on his part, but I had to spend 2-3 hours with a pick taking all that stuff out.

If you aren't a stranger to welding and such, sand blasted material is really nice to work with as a base. A bit of acetone or ethanol to get rid of the small grits and it welds nicely.

Some samples, that is with a harbor frieght blaster, dual air compressor setup. You really can't beat a sandblaster for the odd curvatures and such. 

The ospho stuff you really want to tackle with a wire brush or something before you coat it. The things like the brake booster with the possibility of the reaction disc having fallen out over the last 40 years was easy to just drop off and exchange for a reman. 

[grannyknot]

jkelly, as far as Ospho  (Phosphoric Acid)  goes, you have to eliminate as much of the rust as you can, if you apply it to well established rust like on your brake booster it will never get down to bottom of the corrosion. A bench mounted wire wheel or even some 60grit paper will break that crust on the rust and allow the Ospho to get down to the bottom. The white powder won't show up for a couple of days until it has dried completely and your right, paint will never stick to that, it must be washed off.

Getting rid of as much rust as possible is always the best method, Ospho is better than nothing but it won't penetrate heavy rust.

[jkelly]

1 hour ago, seattlejester said:

The ospho stuff you really want to tackle with a wire brush or something before you coat it. The things like the brake booster with the possibility of the reaction disc having fallen out over the last 40 years was easy to just drop off and exchange for a reman. 

 

4 minutes ago, grannyknot said:

jkelly, as far as Ospho  (Phosphoric Acid)  goes, you have to eliminate as much of the rust as you can, if you apply it to well established rust like on your brake booster it will never get down to bottom of the corrosion. A bench mounted wire wheel or even some 60grit paper will break that crust on the rust and allow the Ospho to get down to the bottom. The white powder won't show up for a couple of days until it has dried completely and your right, paint will never stick to that, it must be washed off.

Getting rid of as much rust as possible is always the best method, Ospho is better than nothing but it won't penetrate heavy rust.

Yeah, that's what I'm learning now. The brake booster was intended to be a test piece that represents the level of rust inside the car's enclosed spaces which I can't access with a rust removal tool.  I was going to see if the Ospho would convert the rust and see how epoxy primer would bond to it with only a water rinse and drying, since that is all I can really do in some areas without cutting access panels or acid dipping. Based on this scrap booster it seems like that isn't going to work -- I'm not even going to bother testing the epoxy on it. I'm probably going to end up cutting access holes to get a grinder in those areas before applying the ospho.

[LLave]

I am going to work on my cowl this weekend. I am going to look around with a borescope and see how it looks in there. Then make an effort to not get too crazy.... Most Z's have a little rust, if it's no big deal I will treat and encapsulate. Last time I said that, I ended up cutting out half the wheel well under the battery tray. 

[jkelly]

23 hours ago, LLave said:

I am going to work on my cowl this weekend. I am going to look around with a borescope and see how it looks in there. Then make an effort to not get too crazy.... Most Z's have a little rust, if it's no big deal I will treat and encapsulate. Last time I said that, I ended up cutting out half the wheel well under the battery tray. 

Good luck! I get the crazy bug. I have to always tell myself not to get to crazy or go too far with it. I feel ya.

[jkelly]

Removed a dog leg this evening. It doesn't look good. Pretty nasty in there. Most of the rust is down low, though, and around the fender lip. Decisions Decisions. I'm not sure if I want to just blast what I can and only replace the dog leg or replace dog legs, rocker, and the fender (inner and outer?)  The more I work on this thing the more shit I find!!! Ahhhh!

 

Edited October 27, 2017 by jkelly

[seattlejester]

Honestly it seems like really only the lower panel is really troublesome. The area near the hinges has some slight surface rust which you can probably get away with a neutralizer and some sealing primer. You can order a patch panel for the outside, for the inside really it is just a matter of connecting pieces and sealing it against rust. You can cut out the bad metal and put in a flat piece like the guy did on project hugo, might add a bit of weight, but no one will see it. Back part of the wheel well can be done similarly as well cut out the piece, then get a flat sheet, bend it to fit the curvature, then tack it in, weld beads for strength, then seam seal for water tightness so water does not get kicked back up in that area.

I guess the question is what the purpose of this car is. Is it a forever car, is it a driver, is it something you think you will sell down the road? What kind of repair could you live with? Will even the smallest bit of surface rust eat away at your conscience? If you don't repair it exactly like how it is will you never trust the strength of it? 

[jkelly]

2 hours ago, seattlejester said:

Honestly it seems like really only the lower panel is really troublesome. The area near the hinges has some slight surface rust which you can probably get away with a neutralizer and some sealing primer. You can order a patch panel for the outside, for the inside really it is just a matter of connecting pieces and sealing it against rust. You can cut out the bad metal and put in a flat piece like the guy did on project hugo, might add a bit of weight, but no one will see it. Back part of the wheel well can be done similarly as well cut out the piece, then get a flat sheet, bend it to fit the curvature, then tack it in, weld beads for strength, then seam seal for water tightness so water does not get kicked back up in that area.

I guess the question is what the purpose of this car is. Is it a forever car, is it a driver, is it something you think you will sell down the road? What kind of repair could you live with? Will even the smallest bit of surface rust eat away at your conscience? If you don't repair it exactly like how it is will you never trust the strength of it? 

Interesting ideas. Are you talking about this section as the back part of the wheel well?

I remember seeing Project Hugo a while back. I'm going to have to do some searching to find the exact pictures -- there's a thread of that build on numerous websites.  It's going to be a daily driver but not when the weather is shitty. It will also see some track days as well. And I may enter it in some car shows, but it's not 100% original and not everything is perfect. I'm doing an L28 swap, aftermarket suspension, aftermarket bits and pieces, etc. I plan to keep this car for a while -- I'm not building it with the intention to sell. I may end up doing another zcar or other restoration that is more of a primary track/race car.

I'm okay treating surface rust with a converter and encapsulating, just not heavy rust like in the picture. I gotta do something about that! On the fender/inner fender overlap circled in red in the picture I would think there's rust all the way around the length of that overlap.

Edited October 27, 2017 by jkelly

[seattlejester]

Yup, mine was similar.

Cut it out to a shape that is easily replicable.

Then spend some time making a piece to replace it. Given its location you can definitely have it be a bit bigger to overlap inwards.

Notice a ton of overlap in my case.

Then weld it in.

My dog legs were bad as well, so I just trimmed off the square portion under it and replaced it with 18 gauge if I recall. You can see the lack of the rear wheel well flange as proof of that panel being replaced as well.

Edited October 27, 2017 by seattlejester

[grannyknot]

Hey your doglegs aren't too bad, at least the shape is still there so if you can't save the metal itself you will have a template for the patch.

[Home Built by Jeff]

I have also torn my hair out trying to paint strip my car. My garage is too nice to fill up with sand, so I first tried paint stripper. It was mostly a waste of time with the 10 layers of paint on my car. I ended up just using the strip discs on the grinder, and even then my back yard was full of dust. Every method is messy, but I think I will have my next project car dipped. It may cost more and I do love doing everything myself, but I think it is the best method for a car with a lot of rust. 

I really enjoy making patch repair panels, although I don't like overlapping, as it makes a pocket for rust in the future. 

 

 

[seattlejester]

Off topic a bit, but real aircraft paint stripper will eat through paint like crazy. It really doesn't care how many layers you have there it will eat through all of it if you apply it on in gobs. Now the stuff is really really really bad for you, the legitimate stuff has a crazy long warning label that will paint a gruesome demise if you do not follow precautions. The cheaper spray on stuff I found doesn't do much other then remove a light coat of spray paint.

Honestly roloc discs are pretty awesome if paint removal is your game. I am not sure how they do on rust, but they will eat everything else away except metal. They are pricey and you have oto have an adjustable speed grinder or else yo will blow the bristles off.

[Home Built by Jeff]

42 minutes ago, seattlejester said:

Off topic a bit, but real aircraft paint stripper will eat through paint like crazy. It really doesn't care how many layers you have there it will eat through all of it if you apply it on in gobs. Now the stuff is really really really bad for you, the legitimate stuff has a crazy long warning label that will paint a gruesome demise if you do not follow precautions. The cheaper spray on stuff I found doesn't do much other then remove a light coat of spray paint.

Honestly roloc discs are pretty awesome if paint removal is your game. I am not sure how they do on rust, but they will eat everything else away except metal. They are pricey and you have oto have an adjustable speed grinder or else yo will blow the bristles off.

I have heard that aircraft paint stripper is the go, but I have not been able to find it here in Aus. The Roloc discs are basically what I have been using and they are great for surface rust.

[331CI 280z]

Be careful using any acid product under certain epoxy primers.    Many epoxy primers are not compatible with acid rust convertors or etch primers.    In the House of Kolor tech manual, it states over and over not to use any acid product under their epoxy primers including etch primers.    Check the tech data sheets on the paint system you plan on using to make sure you dont end up causing more headaches down the road.

[Home Built by Jeff]

26 minutes ago, 331CI 280z said:

Be careful using any acid product under certain epoxy primers.    Many epoxy primers are not compatible with acid rust convertors or etch primers.    In the House of Kolor tech manual, it states over and over not to use any acid product under their epoxy primers including etch primers.    Check the tech data sheets on the paint system you plan on using to make sure you dont end up causing more headaches down the road.

When ever you use an acid based rust converter, wether it is off the shelf, or white vinegar, you need to ensure it is thoroughly cleaned away, no matter what you are topping it with. If the tiniest bit remains, it can cause headaches later. 

[jkelly]

When you guys mention Roloc discs are you talking about the bristle ones or the flat ones? I've used the flat Rolocs. They do work well on flat panel surface rust. Never used the bristle ones.

OR

[seattlejester]

Of course, neutralizing acid products is a must. 

I've only used the bristle ones for getting gasket material off an engine. With a vertical/not angled die grinder you basically have a big eraser. DIdn't know they had flat ones. Depending on the use a wire wheel or cup may last longer for that application.