Blasting advice

robking

New Member
Hi folks, I would really appreciate some advice on how to best get this fender ready for SPI epoxy. A quick history, the fender is sound however had a ton of surface rust. After going over it with 80 grit on a D/A, any where the surface rust had been looked "stained", which I believe is rust down in small pits. I decided to invest in a small HF pot blaster and 40/80 crushed glass from Northern Tool, and practiced on an old door to make sure I avoided warping anything. Ended up using about 60 psi and making sure to keep tip at an angle and not linger too long in one place.

I've been very happy with the blaster and the crushed glass media, but there are still places that have a "shadow". I realize there's pitting there so it will look slightly different, but my fear is these rust pits are so small that my media isn't getting in there very well. There's a place about 2 hours away that sells quality blast media for $9.00 a bag (www.blast-it-all.com) and they have a 70/200 crushed glass.

Would it be worth the drive to pick up this finer media and try going over some of these spots again? Or am I over thinking this (tend to do that).

Any and all advice is greatly appreciated. Any thoughts on what to put over the epoxy to fill the pitting would also be much appreciated.

Thanks,
Robbie

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Chris_Hamilton

Trying to be the best me, I can be
You don't need smaller or finer grit media, just need to go over it with what you have again. The crushed glass media you have now is perfect for what you are doing. The fender just needs probably one more pass with the blaster.

Once it's clean, be careful in how you handle it. Ideally only with latex or nitrile gloves. Once clean, blow it off with compressed air and epoxy it. No need to use W&G remover on it. Ideally you want to epoxy it ASAP.
 

robking

New Member
Just looked it over again with a good bright light, and I think that one more pass in a few spots may be all it needs.

Pretty sure I know the answer (no), but would ospho be useful against these small pits?
 

Chris_Hamilton

Trying to be the best me, I can be
Just looked it over again with a good bright light, and I think that one more pass in a few spots may be all it needs.

Pretty sure I know the answer (no), but would ospho be useful against these small pits?

You could but blasting it would be faster and easier. Plus no worries about neutralizing the Ospho.
 

robking

New Member
You could but blasting it would be faster and easier. Plus no worries about neutralizing the Ospho.
That's my feeling as well, I really don't want to risk adhesion issues. Thanks for the help!

Now I just need to get my little blaster dialed in better, I've gone through two 50lb bags already.
 

Chris_Hamilton

Trying to be the best me, I can be
Dial back the amount of media coming through the nozzle if you can. Not familiar with that particular one you are using, but ideally you want a very light stream of media, less is actually much more effective than more media. Especially at lower pressures. If you have too much coming out it just hits the metal and falls to the ground without doing much. So trying turning it back quite a bit and see what happens. Should see a marked increase in performance and a drastic reduction in material used. Don't worry overly about warpage if you are using a very light stream of media and pressure around 60 pounds.
 

theastronaut

Promoted Users
I keep a block of wood with the blaster and use it to dial in the sand flow valve on the bottom of the blast tank. I start with it closed, let the tank pressure normalize with air flowing out the nozzle, then slowly open the sand valve while pointing the nozzle at the block of wood. The best mix ratio is when the wood is just starting to deteriorate plus a hair more so it's not as likely to clog. Any more and you're wasting sand, any less and the valve is closed so far that it can clog easily from inconsistencies in grit size.

I just did these drip rails and had to spend extra time to get all the rust out of the pitted areas.

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robking

New Member
Thanks guys this is very valuable advice! I think that's more or less where I eventually ended up (accidentally really), was opening the media just far enough to get flow. Then it would clog so I cracked it just a bit more. I really like the block of wood suggestion, will definitely do that.

Also thanks for the vote of confidence on the pressure setting Chris. These Coronet fenders are hard to come by and I've read so many horror stories about warping panels. However you usually just get "the guy warped it" with no detail about media, pressure, etc. Sort of like "you'll shoot your eye out" in Christmas Story. :)
 
you can try stepping up to aluminum oxide or even black beauty at those low pressures. My mentality is start at 12/20 and in a half hour you are using 40/80.

People like glass because it explodes like baking soda when it hits the surface and give you the extra kick.

I would be more concerned with the back of the fender, how much is there that will end up getting back thru, but there is the mentality is you get the epoxy to bite and seal, that light stuff is going to do no damage.
 

robking

New Member
Odd thing about this particular fender, the back is actually in better shape than the front (sanded front and back to metal) due to undercoating (go figure). For whatever reason, when I got it the outside had a coat of etch primer (I'm pretty sure), but looked like it had been driven back and forth through a barb wire fence. For the life of me I can't figure out how somebody managed to do that. But I got it for $25 at the auto fair in Charlotte, so I was thrilled till I actually started working on trying to get it ready for paint.
 
Its why I would step up in media if you want to continue blasting. Those fenders started out so much thicker than the stuff we are worried about warping today. To me there is a fine line in waking up the sleeping rust monster and making it mad that I would agree with the Ospho at this point. Keep mixing a little in water as you are neutralizing it and you will get a beautiful blue treatment on that metal. I wont tell you all the rust disappeared, but you wont see it anymore.
 

Chris_Hamilton

Trying to be the best me, I can be
Its why I would step up in media if you want to continue blasting. Those fenders started out so much thicker than the stuff we are worried about warping today. To me there is a fine line in waking up the sleeping rust monster and making it mad that I would agree with the Ospho at this point. Keep mixing a little in water as you are neutralizing it and you will get a beautiful blue treatment on that metal. I wont tell you all the rust disappeared, but you wont see it anymore.

Ospho removes good metal too. ;) Especially soaking it in the stuff. Messier, time consuming, and you have the risk of not neutralizing it properly especially for someone inexperienced.
It looks like typical rusty old sheet metal. Nothing special or difficult there. What you have (glass media) will work fine. Get your blaster dialed in correctly, it's one more thorough pass with it and you will be good IMO. If you have a few randoms here and there it's ok, if you prime it with (SPI) epoxy.

BTW warpage in sheet metal is a result of both pressure and volume (media). You need both to warp sheetmetal.

Example, 150 psi of pressure can shoot a much heavier stream of media properly than you can at say at 60 psi, your media stream is going to be much less volume. Which is much safer. That's why it's important to tune the amount of media to the amount of pressure you are using.

I think you mentioned in one of your posts shooting it sideways, FYI if you do blast it again, as long as you are using low pressure and volume, angle the gun head on. Don't offset it much. That will make what you are doing more effective. Coming at it sideways like you hear people advise is a crutch for when the media blaster is using higher pressure and volume. You are using lower pressure and volume so you need to hit it head on. You'll notice the difference.
 

robking

New Member
Ospho removes good metal too. ;) Especially soaking it in the stuff. Messier, time consuming, and you have the risk of not neutralizing it properly especially for someone inexperienced.
It looks like typical rusty old sheet metal. Nothing special or difficult there. What you have (glass media) will work fine. Get your blaster dialed in correctly, it's one more thorough pass with it and you will be good IMO. If you have a few randoms here and there it's ok, if you prime it with (SPI) epoxy.

BTW warpage in sheet metal is a result of both pressure and volume (media). You need both to warp sheetmetal.

Example, 150 psi of pressure can shoot a much heavier stream of media properly than you can at say at 60 psi, your media stream is going to be much less volume. Which is much safer. That's why it's important to tune the amount of media to the amount of pressure you are using.

I think you mentioned in one of your posts shooting it sideways, FYI if you do blast it again, as long as you are using low pressure and volume, angle the gun head on. Don't offset it much. That will make what you are doing more effective. Coming at it sideways like you hear people advise is a crutch for when the media blaster is using higher pressure and volume. You are using lower pressure and volume so you need to hit it head on. You'll notice the difference.

Thanks Chris, I did notice a difference coming at it straight on for sure. I'm looking forward to the next decent day I can put all this good advice in to practice.

Add far as stepping up the media, I do have some black beauty from tractor supply. However I've been trying to err on the side of caution. I'll see how dialing in the blaster with the crushed glass goes first.
 

JGR

Promoted Users
Just looked it over again with a good bright light, and I think that one more pass in a few spots may be all it needs.

Pretty sure I know the answer (no), but would ospho be useful against these small pits?
no!!!
 

jelco

Promoted Users
Where did you blast the fenders? I’ve seen people on YouTube do it outside but then you’re unable to reuse the media.
 

dhutton01

Promoted Users
I don’t reuse media. The juice isn’t worth the squeeze imho. I think I pay $7 for a 50 pound bag at Northern Tool. How much time to scoop and screen the media? Then the inevitable clogs that need to be cleared.

Don
 

JimKueneman

Mopar Nut
in my blasting business we use star blast. it is a fine media . great for getting the pits . i keep the nozzle at 45 degrees stand off 2ft and run about 45 lbs with media turned down .

Agree with Shine. I use coal slag in the first pass if it is very rusty then a few go overs with Starblast. I reuse it so every time I sweep it up and sift it it gets finer and finer so it automatically sizes down to get the smaller deep pits clean.

Also Coronet? I NEED PICTURES!!!!!!
 
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