I am not sure I ever painted POR directly on rust as they claim. I always tried to remove the rust in some manner. But your statement supports the KEY part of prep, get rid of ALL loose debris. Prep is the most vital part here.

 

Yeah, it was my friend's car. The whole rear underbody was very rusted from a decade + of salted winters. He didn't care about the car but didn't want the car to end up junked out too early for money reasons so he was trying to stop the bleeding. He did take a handheld stiff wire brush to everything he could touch without any disassembly at all. Bad thing is the rear sub frame was a very rusty mess (too rusted to feel safe using in my opinion) and a quick wire brush job didn't cut it for prep with how bad of shape it was in. When we went back to do rear brakes about a year later, there were several small spots of that had chunked off.

Everywhere else held up great though as nothing else had the extent of rust that the sub frame had - even though the vast majority was painted directly over the attached surface rust. I do agree that the more prep the better, he was just lazy / didn't really care about his car - and even at that it did a great job overall.

 

Ok, so I will use POR-15 as planned, however, theres no way im going to get POR-15 inside the support rails of the car, so what am I going to do about that? those rails are structural and if I neglect them, then they could rot from the inside out. Perhaps I could use woolwax on these since this part of the car is less exposed to the elements and less likeley to wash off as quickly as if it were under the car, but I dont know. I've already ordered all my Paint and clearcoat for my repair job, I have yet to order the POR-15, but I will do that when it gets warmer.

I was wondering if i should go over the underside with 80 grit sandpaper just to make sure the por 15 sticks to it better, but i dont know if that would ruin it, probably should just stick to flat metal.

 

There are tools to spray POR15 (and require the proper paint thinner for POR15). Some of those tools would let you maneuver into those hard to reach spots and coat POR15 in them. I don't know them off hand, but they would be no different than tools for applying paint in the same spots.
Remember, the more pours the metal has, the better POR15 adheres.

Here are some current pics of my mom's LeSabre. I did top coat with paint that matched the car, but it did not adhere to the POR15 (I am going to say it was a lack of proper prep for the top coat). But, the POR15 is holding pretty good. I used just a wire wheel to remove loose material, applied the metal prep spray and then brushed POR15 on. If I could have sand blasted, results would have been even better. The seam on the inside of the door is a pain point. There is no practical way to get behind the crimped spot of the seam, hence rust can creep back (and there are signs of that). But it has certainly slowed down the rust.

 

I happened across a neat video I wanted to share. This guy runs a YouTube channel called "Project Farm" and I really like his approach to product testing. Anytime I have seen something, I felt he did a very well thought testing plan AND he makes it clear he is NOT sponsored (so his results are not bought, they are honest). He tested a variety of rust encapsulating products. Before viewing, I will say two things:
1. - POR15 did come in first
2. - He actually did NOT follow the best recommendations from POR15 (I did not see that he used the "metal prep" spray). That being said, it is possible a similar situation exists with the other products he tested.

This is a good watch:

 

Its funny I actually watched that same video a few weeks ago haha, yeah I stumbled on his channel and watched some of his content, i really like it, he does good thorough reviews. I will definitely go with por 15 for my undercarriage. My only problem with doing the inside of the frame bars with por 15 is that im worried it wont stick to it and i keep having to monitor it with a borescope. I was thinking of just using por-15 on the underbody and wool waxing the inside of the frame holes, but i could use por 15 if its not bad in there, i would give it a couple coats. considering its on the inside of the frame, i dont have to worry about rocks and water hitting it so i think it will be ok without the prep stuff. I still havent ordered the por 15 yet. im still trying to figure out how much i need. I'm thinking just 1 quart of black and 1 quart of grey. I want to do 2 coats like they suggest just so I have the best chance possible and dont wind up re doing it.

I'm thinking of ordering 4 of the smaller containers, because as you mentioned, once the can is open, it starts to dry fast and if i close it up then im not getting it back open. it's getting warmer out and today I went and bought a fuel tank pressure sensor and replaced it because the code for it was on. pretty simple job, im getting more comfortable with doing that stuff myself. next is my multifunction switch.

I already got my paint and clearcoat ordered from automotive touchup, should be here on the 8th, so that will be nice, my paint is looking terrible. Since you posted that pic of your moms car, im wondering if i shouldnt put por 15 over the spots i will bondo since the paint fell off. im diggin ALL of the rust out, not a spec will remain, and then i will bondo it and paint it. I have the dremel and that has been wonderful with he cone grinder tip for digging out rust, although i have to order more since they lasted about 15 minutes haha.

 

It's not that the POR15 dries up fast. I have worked out of the same can for a couple of weeks. BUT, when you close the can, using plastic wrap or a plastic bag between the can and lid is critical (I had a lid bond really good with the can once). *IF* you finish and don't know when you will use it again, jars (glass jars) like baby food glass jars work great to store it!

I mentioned before, there are products to get wands or spraying devices into those cavities. And you can spray POR15 (it would be recommended to also use their paint thinner). I don't know the best things to recommend (I just know they exist, my father used a wand to spray POR15 into a cavity on a 1973 VW Beetle years ago). If you have an automotive paint supply store, stop in and talk with them. I am sure they can help.

 

Accidentally posted this somewhere else, oops.

Ok so ive been collecting tools and equipment over the past few months and this is some of the stuff I got:

POR-15 - the star of the show. I dont think 1 pint will be enough so i will order more, but i think the degreaser and cleaner will be enough as you dilute it with water so theres more in there to use.




My new transmission filter and gasket. The new pan with the drain bolt is still on its way from Tennessee.



8 amp dewalt corded drill. I decided to use a corded drill because it has more power, this thing is powerful, i tested it out, it will do a good job removing rust.



Tyvek painters suite to preotec tmy skin and clothing from the POR-15



3M respirator with filters. I have 2 more packs of 2.



24 inch half inch drive breaker bar



2 Gallons of Dexron 6 ATF fluid i bought today



An assortment of tools including an oil filter wrench.



Portable steam cleaner for deep cleaning the interior carpets and trunk





2 ton floor jack




Plastic oil catch pan




Dremel, this thing is pretty cool and will be handy around the house as well.




Serpentine belt tool to assist when i replace the alternator at some point.




Torque wrench which i think i might return and buy a better quality one.




Cleaning supplies and other assorted stuff




Art easel boards i will use to mix bondo on, i will put parchment paper over them first.




Custom mixed paint for my montes color and clearcoat plus bondo. I got adhesion promoter for the bumbers cause the back bumper ist looking too good.




An oil spill mat with rubberized bottom to help catch oil spills when i do the transmission and engine oil.




5.5 HP shop Vac to clean out the car with.




4 2 ton jack stands




I also ordered a plastic chisel set from amazon to help remove the gasket if its stuck on so it doesnt gouge the metal but someone stole it! so now i have to order it again.

 

Impressive! Nice collection! When you use those boards to mix bondo, wrap them with something like aluminum foil. Then when you finish, take the foil off and DONE, board is clean for another use.

Also, I saw the trans filter. I am going to make a recommendation. The gasket that comes with ALL filters is a flimsy, cheapo rubber one. I always changed the trans fluid and filter every 100k miles. Those gaskets eventually get brittle and begin leaking fluid LONG before the OEM gasket. When you remove the OEM gasket, it is a metal core gasket. Some claim a re-usable gasket (I never found a claim from GM on that and if you are changing fluid every 100K, time for a new one in my book). My opinion, get an OE style, metal cor transmission pan gasket. Benefits: it will be easier to install AND it will last way better than what came with the filter. Here is an example of one from RockAuto (and they have others like that, I have used ATP before):
https://www.rockauto.com/en/moreinfo...t=8612&jsn=978

 

Thanks! I probably spent clost to $2K on all that stuff. I also bought a stretchy garden hose and an attachment so i can hook it up to my shower faucet and put it out my bathroom window so i can spray all the por 15 metal prep and degreaser off. Thanks for the tip about the gasket. My new pan is still stuck in Tennessee so i cant change it anyways. Is the one in that link for my monte? I plan on changing my transmission fluid every 30K miles from now on. Idk how long to go for a filter change, maybe the same amount.