Prep for Epoxy question

9

95BlackTT

Hi I have an engine bay I am working on currently and had a few questions about prep before applying epoxy.

First I have sanded most of the engine bay with 80 grit but not all to bare metal as you can see:
View attachment 1457

Can I go ahead and do a wipe down with 700 after cleaning and masking or do I need to get it all down to metal? I was hoping to use a red scotch pad for the crevasses and was unsure if it was ok to have 80 grit scratches and 400(?) grit scratches on the same panels.

Secondly I have some rust spots from plug welds where some panels have been replaced and was wondering what the best solution is for eliminating/ converting the rust. This is what I am talking about:
View attachment 1458

I've heard removing the panel and rewelding it is the best solution, however I don't have the means to do that.
Thanks in advance.
 
what about a wire wheel or one of the roloc scotch bright pads? Rusty's posted some great threads that are near tutorials if you haven't already seen them.
 
Some OE finishes are OK for epoxy, like most stuff that's less than 20 years old or so. But any remaining paint should be smoothed out with a finer grit like 180, 80 marks in paint can easily show scratches later due to shrinkage.

Your rust should be spot blasted with a hand held media blaster.

We do not prefer wire brushes for final prep because they can polish the metal somewhat and reduce adhesion.
 
What crashtech said. I have a cheapo Harbor Freight spotblaster...push it up tight against the weld spot, three quick bursts on the trigger, and the spot looks like new and you don't have a mess of sand everywhere because it goes back into the gun. I also use a wire wheel, but if I do this I go back over the area with a DA to restore grit for adhesion.
 
I'm just gonna tell my story in support of Crash.
My project is a 58 GMC I wound up with in partial payment for a kitchen remodel back in 09/10.
I wire brushed and sanded the inside of the fenders and got rid of the road tar 'as best I could' and hit it with several coats of rustoleum. The truck has been garaged nearly all of that time, move to last spring. I finally get around to pulling the fenders and hit them with some air and the paint lifted in 'x' sheets.
By now I've learned about SPI and figure no problem I'll just sand it all down better and then normal clean and prep. Cool.
Two months later I'm blowing off the SPI epoxy in sheets too.
After a quick call to Barry in which we (he guides me) decide its tar and its "In the pores"(my words) and I realize it would take a qt of reducer and several more hrs of scrubbing to really get it out I admit defeat and start looking for a blaster. Turns out my buddy has one sitting since he got it in the trailer a mile away. I'm remote so it took a little searching but finally found a local company that uses a green diamond sand out of S Ore. I built a 3mil painter drop booth out of patio door screens for panels over the bench in my garage and set out a blasting.
The metal was so nice after blasting (about 60lb/psi and the sand feed as low as I could get it) I couldn't tell the difference between it and the good SPI epoxy where it was clean underneath. I wondered if that was by design or just coincidence. I just started laughing. I was laughing at my years of resistance by wanting to try all these other ways of dealing with rust that in the final analysis just wind up looking like posers compared to what I wound up with. Well that, and feeling stoopid like I was the butt of a Colbert joke.
If you have even a small job compressor a small 10#lb/about 1.5gal? pot it would be worth it. And then a good shop vac and a pressure washer becomes your friends next!
 
Yeah I have a 60 gal compressor and a 30 gal. I am working today on getting some metal piping ran for my 60 gal and hooking up my new water separator, filter regulator. Yesterday was the first day I have used that compressor in the summer and it was like a sprinkler at my tool. I also have a little blaster and currently have 10lbs of GLASS media NOT sand. Do you think glass will be ok or do I need to get sand?

As for my sanding prep, Do you think it would be ok to just run over the engine bay with 180 where the are spots of paint, primer and bare metal? Or should I just bite the bullet and sand everything down with to bare metal. The car had a cheapo paint job on it so I wanted to make sure the remove that but the primer underneath is fine, the car is a 95 toyota BTW. Thanks.
 
Crushed glass yes, glass bead, no. Glass bead gives a nice surface finish but is not "toothy" or rough enough for primer.

Getting rid of all the paint is best, but if it is undamaged factory finish and/or primer it's probably OK, if it is smoothed with 180. Any refinish (not factory) paint should go, not only because the quality of the material is suspect, the prep on low end refinish jobs (and some higher end ones, too) is likely to be poor or nonexistent in hard to reach areas.
 
Ok, so I got back to work on the car and have a question for you guys that do some blasting. I got some black bull No. 80 sand to use in my blaster for the rust spots and was wondering if I could also use it to blast the hard to get to spots around the engine bay. This is probably a dumb question but if the sand says 80 grit does it actually leave an 80 grit scratch? I tried a spot next to a place where I used a DA and 80 grit and it doesn't look as course. I would like to finish blasting the spots that still have factory primer, clean up everything and finally get some epoxy and 2k sprayed. Thanks.
 
Thanks, Crash for the help. I got 2 coats of epoxy on then realized I don't have a gun that will shoot the 2k that well so I had to order one.

I have a question about fillers as I have a few places I want to use some.

When is it appropriate to use bondo vs fiberglass filler and vice versa. I know the lightweight filler is for those small inperfections before sealer.

Also, since I will be outside the 7 day window for the 2k, what do I need to sand the epoxy with? Will a red scotch brite work? I plan on doing another coat of epoxy then the 2k. Thanks
 
Forget about the fiberglass filler. Just use regular filler on the epoxy.

I think scuffing with a red scotchbrite is perfectly acceptable, especially when recoating fairly fresh epoxy with more epoxy, however, some will say 150 or 180 by hand is best.
 
A maroon scotchbrite works just fine for scuffing epoxy, do yourself a favor and use a quality filler-Evercoat Rage Gold, Rage, or Rage Extreme all get my vote and never any problems. Lightweight filler isn't just for those small imperfections before sealer and you shouldn't be shooting sealer over any bodyfiller-a sealer coat is for between your final sanded perfected primer or sanded painted surface and your paint. Fiberglassed reinforced filler adds some strength and is a little more moisture resistant compared to regular fillers-IMO the only place it's an advantage is over areas that may benefit from these qualities. What 2K do you have? What guns and tip sizes?
 
I'm using Spi epoxy, spi regular 2k, dupont base, then spi universal clear. I ordered the devilbiss startingline primer gun with 1.8 tip for the 2K. I have a sata rp 3000 with 1.3 and 1.4 tips for basecoat and clearcoat respectively. I have an hvlp ingersol rand with 1.5 tip that I used to spray the unreduced epoxy. I was thinking of using the sata for my reduced sealer epoxy coat but not sure which tip to use. I worked for a bodyshop as a buffer/ painters assistant in high school but that was 12 years ago and it was collision repair not the restoration type work I'm trying to do on my car now. So thanks guys for the help.
 
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