I seen a few rust bubbles starting over the rear fender well on a 96 Ford F-250 that I wanted to address before they got any worse. I pulled the box off and removed the inner bulkhead so I could get to the rust better and it turns out it was only a few small rust holes. I ended up grinding the few rust holes back to solid metal then welded the holes shut which was more of a pain than I anticipated but I got them welded finally after a million burn throughs. Now I'm ready for Primer and Body filler and plan on using Spray Max 2k Epoxy Primer and light weight filler. Is anyone familiar with the Spray Max rattle can primer and will it seal out moisture ? Should I Spray the primer first or apply the body filler first? Also I got new inner bulkheads and was debating about using only 3M Panel Bonding adhesive using clamps to install them and want to avoid welding if at all possible. From what I gather it can be done without welds and the adhesive is a much stronger bond than spot welds when cured. I'm sure I read that in some 3M tech sheet a few months ago but haven't found that source to confirm it. Anyone?
Auto Body Epoxy Primer / Bondo Questions
- Thread starter i4ni
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CraigStu
Well-known member
From their website, "Excellent adhesion and corrosion protection properties" so looks pretty good. Primer never used to be suitable for sealing but epoxy primer is much better. I would still put several coats of paint on it. I haven't used it myself but have seen many videos using the 3M Panel Bonding Adhesive and I would use it for what you need in a heartbeat. There used to be a TV show that showed how various cars are built. It is amazing how much of some exotic cars are put together w/ aluminum and carbon fiber pieces being attached w/ epoxy including structural areas.
Bill Bowman
Well-known member
Epoxy primer before body filler. You should sand the epoxy to "rough it up" prior to applying filler. The 3m 8115 Panel Bonding Adhesive does work well when the directions are followed. Personally, I would want a few tack welds on the panel that you're replacing. I use 8115 on a regular basis, and have had very good results.
ScottsGT
Well-known member
Clean, dry bare metal and apply the epoxy. Let cure 24 hours before applying any bodywork. And yes, the "new" panel adhesion systems work great. I say "new" because when I did this for a living these bonding systems were just coming out for SMC panels and not metal at the time.
nadogail
Well-known member
In High School auto shop, late 50's we removed all the rust and welded or brazed patches in place before applying lead. Copper pennies were often used to patch holes where moldings had been removed. Lead was the method of choice at the time, we were just starting to hear about Bondo.
ScottsGT
Well-known member
Read the directions of the epoxy primer first. When I did my '66 GT Fastback I had a long conversation with the owner of Southern Polyurethanes Inc. As he told me, Epoxy primer is exactly what the name implies. It's like an epoxy adhesive. The surface will not cure for ** days and you are good not sanding up until that time. If you apply too soon the primer and epoxy will react with each other (this is what I experienced and why I called him). With his products, it was a 24 hour window before applying anything on top. And I think up to a week before having to sand the surface.
Even applying fillers, same as primer on top. he told me in areas I knew I needed to apply filler but didn't have time to work them out to go ahead and apply the body filler after 24 hours if I was not going to be able to return to the work within the 7 day window. That way I would not have to sand the surface before applying the filler.
He actually had me do an experiment at home to see how epoxy cures. He had me spray a clean piece of metal. Let it sit until it was dry to the touch and then take my fingernail and scratch off the epoxy. It came right off. 12 hours later, do it beside that spot. A little more difficult. Another 12 hours later, do it again and keep doing it. It kept getting harder and harder. I think after 24 hours I could not scratch with my fingernail. You could actually see how the primer was curing and biting into the metal.
ScottsGT
Well-known member
I can gladly say I never had to do lead work. My instructor in Auto Body back in 1981 was an old school guy that was 75 yo at the time. He had us do some lead work in class so we could appreciate the ease of using polyester body fillers.
Metal-Marc
Well-known member
On raw steel, I treat with phosphoric acid, then seal it up with two part epoxy primer.
Then 2K primer or skim coat of bondo to make it look nice.
Sanding in between coats. Lots of sanding, then some more sanding. Once you're done sanding, you sand some more.
Eventually you apply your base coats and clear coats.
Then 2K primer or skim coat of bondo to make it look nice.
Sanding in between coats. Lots of sanding, then some more sanding. Once you're done sanding, you sand some more.
Eventually you apply your base coats and clear coats.
ScottsGT
Well-known member
LOL!! When I was prepping the Mustang for paint, I was going through this stage. My wife asked me why was I not putting the color on it yet. It looks the same today as it did two weeks ago.
I told her if I painted it now, she would understand why I'm still sanding. But I'm not fast forwarding to the finish coat just so she can see how bad it looks now.ZRX61
Well-known member
I hit the bare metal with an #50grit 5in disc with the air turned down so it really digs into the metal. No need for more sanding after that until after you get the filler or Featherfil applied.
From PPG:
"It is no longer recommended to use an etch primer under an epoxy primer. Residual acid from the etch primer can interfere with the proper curing of the epoxy. This may lead to extended dry times, potential blistering, and even adhesion failure"
Slednut
Well-known member
I'm not trying to denigrate the replies so far, do yourself a favor and go here and ask your question.
Learn how to paint your own car!
The #1 site on the Internet to discuss and learn about autobody and paint. If you want to learn how to paint your own car, this is the place!
www.autobody101.com
56Mark
Well-known member
I agree. Go to SPI's website and read. They have good forum too. Barry that owns the place is a car paint nerd if there ever was one. i went to one of his seminars years ago at a local car show, nice guy. He knows his stuff. I think they make the best products on the market. Personally, if I wanted it to last long term, I would stay away from rattle can stuff. Sand with 80 grit, coat with SPI epoxy and it will last a long time.
ScottsGT
Well-known member
FWIW, The Mustang I did with SPI.
dcs13
Well-known member
SPI all the way. Shot some today as a matter of fact. Their epoxy has a 7 day window (you can apply filler in first 7 days WITHOUT sanding the epoxy) . So proper prep, SPI epoxy, I wait at least 24 hours before filler, then 2k, base coat/cc when your satisfied with your body work/primer blocking.. And yes, the SPI forums and Facebook groups are awesome.
Slednut
Well-known member
Now if we could get a filler primer that we could guide coat and sand that has the same chemical bond to the base coat.
metlmunchr
Well-known member
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- Sep 10, 2011
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Another confirmed SPI user here. If you don't have spray equipment, IMO you'd be far better off to buy a quart of epoxy and a quart of activator from SPI for about $100 total and brush or roll it on rather than spending roughly the same amount on 4 spray cans.
All epoxies are not the same. SPI is a high build product that sands fairly easily, while many others require multiple coats for the same build, and if you need to sand them, sanding is about like rubbing sandpaper on a concrete slab.
I replaced the rockers and cab corners on my 92 Chevy pickup using the 3M panel adhesive about a year ago, and it worked great. One of the advantages to adhesive is the fact that the entire seam is closed off from water and future rust. On a spot welded lap joint, the first place rust will come back is in the lap as it's a perfect place for dirt to collect and hold moisture.
If you do use adhesive, go ahead and spend the $65 or so for the special caulking gun that's made to push both tubes and use the disposable mixing tips. The adhesive is expensive and you don't want to end up wasting a bunch of it via some makeshift method of dispensing and mixing by hand. I gave the same advice to a friend who was doing the same repairs on his truck, but he's too much of a tightwad to spend the money on the gun. I didn't offer to loan him mine as he's too much of a slam bang type of "craftsman" to trust with any of my tools. He ended up using 3 tubes of adhesive @ $45/tube where one tube was plenty for me to complete the entire job. So, he unnecessarily blew 90 bucks on adhesive and still ain't got the gun.
All epoxies are not the same. SPI is a high build product that sands fairly easily, while many others require multiple coats for the same build, and if you need to sand them, sanding is about like rubbing sandpaper on a concrete slab.
I replaced the rockers and cab corners on my 92 Chevy pickup using the 3M panel adhesive about a year ago, and it worked great. One of the advantages to adhesive is the fact that the entire seam is closed off from water and future rust. On a spot welded lap joint, the first place rust will come back is in the lap as it's a perfect place for dirt to collect and hold moisture.
If you do use adhesive, go ahead and spend the $65 or so for the special caulking gun that's made to push both tubes and use the disposable mixing tips. The adhesive is expensive and you don't want to end up wasting a bunch of it via some makeshift method of dispensing and mixing by hand. I gave the same advice to a friend who was doing the same repairs on his truck, but he's too much of a tightwad to spend the money on the gun. I didn't offer to loan him mine as he's too much of a slam bang type of "craftsman" to trust with any of my tools. He ended up using 3 tubes of adhesive @ $45/tube where one tube was plenty for me to complete the entire job. So, he unnecessarily blew 90 bucks on adhesive and still ain't got the gun.
ScottsGT
Well-known member
Not sure what your asking for here. If you apply the SPI Epoxy and give it 24 hours and use their 2K high build you get what you are asking for. Now are you asking for a high build primer that you can apply over the fresh epoxy primer that is less than 24 hours on the panel?
ZRX61
Well-known member
I start with epoxy under the Featherfil G2 etc, then after it's all blocked out & ready for color I put down another coat of epoxy as a sealer coat.
You guys talking about SPI reminded me that I bought some 2k primer from them for a project that I went a different direction with several years back. It was never opened so I assume it should still be OK. I need to do some digging around to find it but I believe it was epoxy not urethane. I'm gonna go look for it right now.
56Mark
Well-known member
Might call SPI and ask them about that. I think the activator has a shelf life....especially if it was opened at all. Always cap it quickly when using; I think the moisture in the air reacts and shortens its shelf life.I found it. 1 quart SPI 6610-4 epoxy primer and 2 quarts of activator which is oddbecause it's a 1:1 ratio. I better look to see if there's another quart of primer here somewhere
I'm trying to think when I bought it but I'm thinking it's been 7 or 8 years ago or longer. Forgot all about having it till now. The other bad part is the spot I need to primer is about the size of a dollar bill x 2 counting the inside.
I'll touch base with SPI but I'm thinking either way I'm going to use the Spray Max primer just to get the truck back together and hopefully re-paint the whole truck next year when I have more time. The Spray Max is a 2 part epoxy with an activator also inside the can that you use a plunger to release and mix the 2 parts together with about a 8 hr window to use it. Hopefully I'll be able to use the SPI for the re-paint but if not it won't be the first time I pissed away money in the wind. lol
tjansson
Well-known member
I would opt to use panel adhesive where appropriate, especially on blind repairs where you can't get to the backside, because weld thru primer doesn't really work. From what I've read adhesive isn't great for patch panels (you'd have to glue some backers in there to make a flange) because it will expand and contract at a different rate than the metal and crack the paint and filler. Maybe this is BS, I dunno...