Welded a bunch of patch panels in the old truck and want to slow down the re-rusting. Should I put the POR-15 on the bare metal and then Bondo or the other-way around? Thanks
POR-15 does not stick well to clean bare metal. I have seen it come off in sheets. it likes to have something to grab.
... not just "something", it has to have rust to attach to. POR15 is not meant for new or clean metal, period. Posted using the Full Custom H.A.M.B. App!
On the other hand, POR does not offer very good adhesion properties for anything else to stick to it either. You'll have bondo falling out in chunks... Media blast the area and spray with epoxy primer, it is actually designed to use with other products..
If you're doing bodywork over it, use a quality Epoxy primer designed for the bodyshop industry. Make sure its rated for "direct to metal" use. (No etch primer required) My opinion...POR15 is for use on frames and internal structures. For exposed panels that are visible or will be getting bodyworked or painted over you are better off with the systems designed for the bodyshop industry.
I'm a POR dealer and I tell people, as stated above not to apply on clean metal, I use epoxy primers on that but if you have surface rust you want to stop by all means try the POR on that. I just had a car back in my shop that I did the rusty section of the frame with POR in 1999 and it is still on that piece today. POR certainly has it's place it just has to be applied on the Right Place so to speak.
You all need to read the lable on the can of POR 15 and then tell me what it says. Then do what the can says and use what the can says then tell me how it works.
Here's the instructions. http://www.por15bc.com/por-15.htm Ill spoon feed you this part : Please note: This product is unlike any other paint or coating you have used in the past. Please take time to carefully read the instructions from beginning to end before using POR15. TO COAT SMOOTH METAL SURFACES,i.e. new metal, or any aluminium/galvanising, Surface must be dry and free of grease, oil or other foreign substances which can be removed with our water based product Marine Clean.
Never knew the stuff had iso's. It's a wonder the long arm of osha lets them sell to the general public....
I think its considered an "Industrial" product, which would come under different rules than products intended solely for automotive use.
All this talk of filler over epoxy, I have to wonder what the advantage is. Fill has LIQUID COMPONENTS in it's make up. They creep into whatever substrate it's spread over and then get aggravated by the solvents in the primer and paint. Over bare metal it simply cures and you're done. Over epoxy that liquid seems to never dry completely and you end up with a 'visit' from your repair weeks later or the 1st time the surface gets heat cycled. All that ultra flat blocking and feathering you do the day it gets applied may also be gone in 24-36hrs due to shrinkage. You can try hard to argue this point but it happens. The only place for fill that I've found safe is well ground and cleaned bare metal or in thin applications over polyester substrates like fiberglass or polyester primer. If you're really good at feathering to near transparent levels you can let fill get over OEM paint but it has to set overnight before you prime over it. Th-Th-Th-That's all folks...
Due to never having filled over Epoxy and never having had issues with filling over bare steel, I tend to agree. BUT, from his question it seems he needs something to keep the steel from rusting over a period of time before he has the chance to complete the bodywork. Given that, it's my opinion that Epoxy is better than the POR 15 he intended to use. Besides...the Epoxy will be easier to grind off if he chooses to fill over bare steel at that time, and up to that time will have protected the metal MUCH better than regular 2k or lacquer primer. Actually...perhaps there is a better solution to preventing rust that might be easier on the wallet! Anyone have any good suggestions for him???
I've done filler both under and over epoxy and never had a problem. But I've pretty slow and usually everything has DAYS if not more, to cure before I put anything over it. I believe they used to recommend it, because epoxy has such good adhesion, and corrosion resistance. In any case, Kosmoski recommends doing it with his epoxy primer, so I'm good with that. Getting back to the POR-15 stuff. I wouldn't use it over, or under filler. Under filler should be clean ground metal, or cured epoxy. Putting it over doesn't do anything, as POR's greatest quality is it's bonding to the metal, NOT plastic. As for the rest, I also use POR-15 silver as a primer on chassis and undercarriages that I've blasted clean. I use their Chassis Coat over it, either gloss or semi, depending on the look I want. If it works well on a frame, I think it works real good! The only time I've had poor adhesion was on fresh, non sanded new metal, or if it's damp, or the temp has changed drastically and the metal might be sweating. I always use it behind patches I've installed, to seal up my welds, and prevent further corrosion.
Rust is definitely a thorn in our hobby!! Working on a 56 Chevy,I have the body on a rotisserie and while scraping off the undercoating there is paint,primer and what seems to be light coat of rust,not rusted thru because the other side has primer on it. so if the rust is sealed from the elements will it stabilize?(POR15 does that?) I have also seen in the past on other cars while sanding for repairs a light coat of rust around and under filler, and the filler is tight and not falling off. I believe that using like materials(polyester) or epoxy there is a better chance of non reactions. I'm not a Professional just a amateur hack! All this Chemical stuff makes my head hurt. As said before the directions on the can is your best course to follow. Pete
I'm going to chime in here... I too have applied filler over epoxy with no issues, great adhesion and great corrosion protection, although not as good as it used to be...no lead anymore! For epoxy I have been using a PPG industrial product called CRE. It's a direct to metal, tintable. sandible epoxy, and this stuff fills awesome. Ok for welded in panels...can ya get to the backside of you panel? If so dress the area, clean it, and spray the snot out of it with 3M rust fighter I. It will seal the backside from moisture, air, I.e things that cause rust. Now for the front....solid welds? Ground clean? When you are satisfied with that.....use a fiberglass reinforced filler as your first skim coat! It's " water resistant" ..... Not gonna guarantee it for life..but much better than normal filler...which is talc and resin....talc can soak up moisture much easier then fiberglass reinforced filler. At the end of the day rust is a {[}%%}^}# and taking these steps can help it stay away for awhile.
I've heard of guys who will apply a skim coat on old metal , a coat of a dura glass type product with resin added. Then block that down and use that as water proof base for what ever is coming next. Now as far as I can decipher that's a older trick & much older than epoxy primers and gives the same concept. It sounds like it would give a better adhered base to the metal and then to the next layers of filler work.
lots of good advice here, my thoughts are always to seal the metal before using filler, Thought(doesn't filler have moisture in it?) so applying filler on bare metal will create moisture barrier and you will have 1, bad adhesion to metal and 2,moisture to metal issues...just my too C's...I always epoxy before applying anything...I have however used por15 on bare metal that has been wirebrushed like frame rails and a rougher surface
Filler doesn't have moisture in it. In certain weather conditions I've been told it MIGHT be possible for moisture to form under it as it creates heat while it cures...but I'm not convinced. Seems possible...but? Regardless...whichever course you take, Epoxy or not, follow the instructions and you should be good. I've never had or seen a problem with filler that couldn't be traced back to poor mixing, poor surface preparation or sloppy underlying metal work etc.
It could be due to poor mixing or talc absorbing H2O but it was still there when I stripped my truck and the 'repair surface' gave no clue this was underneath.
Avanti, almost all failures like yours probably stem from the fact that a lot of repair guys didn't do the prep work right. I've seen guys fix dents, that have been expose, due to cracked paint, by just filling the dent, over rust and paint, or just giving the surrounding paint a light grind, and fill, again, not removing the rust. In the business, as long as it lasts a couple years, it's a good repair. Remember, at some point in the past, these cars werent' worth much, and didn't justify doing high quality repairs, like the do now. Though I still see low quality stuff being done all the time!
For what it's worth, POR-15 works very well as a protective undercoat if the bare metal is prepped well. The Falcon floor pans are hard as a rock in POR-15. If scuffed and cleaned, it's coated easily with whatever you want, afterward. The Kustom Falcon Build: http://www.jalopyjournal.com/forum/showthread.php?t=734282
I guess I'm just a picky dickhead, and we can add old-fashioned to it as well. Reality checks should apply though. I always want perfect and perhaps optic surface quality. I'm able to read too much on a car's surface. The swelling I mention may not happen at all, but having seen it happen over 2 coats of DP (not DPLF) I just won't do it. As mentioned, cure time is a very good thing and the best defense is thin layers of fill over better metal finishing. There's also etching primers that work well to preserve as you work. I guess if it's planned to sit in bare metal for months at a time you need to something, but I still grind back. As far as rust prevention, what are we really preventing? Will your hard work see salt? Will it sit in the parking lot at your job 40hrs or more per week? Will it be subjected to daily highway abrasion? Right hand raised, mine won't. POR-15 is awesome when used as directed. Not the best underbase for much of anything but as an inside coating or pinch weld seal it's hard to beat.
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