Iam a little confused on my options as far as applying some sort of undercoating to the tub and inner body panels. I have been working on stripping off the old undercoaing, dirt and other debries from the underside of the bronco but I have not stripped it down to bare metal in most cases. There is some red primer showing in allot of the underbody areas, and in some areas up under the rear quarter panels etc Iam unable to get in there really well.

My original thought was to coat the under body with POR15 Chassis Saver. However to complicate things the more i cleaned the more I removed the old seam sealer, which now I will need to replace. In adding new seam filler they recommend using a primer before applying it. So it would look like this:

Underbody - Primer - Seam Sealer - Top Coat ( Chassis Saver in my case)

So the problem Iam now having is the primer..

I was thinking of using an epoxy primer which I guess I could mix with a sealer and spray that onto the underbody and be done with it. However it will react to the left over factory primer...

Any advice on this? I want to make sure I do this right, but remember that the truck will be blasted and painted in the next year or two and I will probably have to deal with teh underbody again at that point.

Remember iam working in a VERY limited space and will have to apply the undercoating while in most cases on my back. I have been recommended to pick up a PPG cup and bag set so i can spray at any angle.. but this is getting complicated real fast and dont want to make one time expensive purchases when there could be alternatives that save time and money with the same outcome.

Do i need to keep working on the underbody to get down to bare metal? I would guess this would add about 2 -3 weeks to my build due to the time restrictions and lack of space..

I cant give you all of the answers but can tell you that POR15 is not to be used on bare metal, it is designed to adhere to rusted areas and convert the rust back into a solid product. As for undercoating, that stuff has ruined more vehicles than it has saved. Most areas that rust has formed in older vehicles is where water has entered an area and was not allowed to drain because of undercoating, so it sits in there and soaks through.

Your epoxy primer should work fine as a sealer, but if I was you I would wait until you are ready to do your sandblasting and coat the entire tub with one product. It seems like your taking 2 steps forward and 4 steps back with the direction your going. If you just want to protect the bare metal until you do sandblast it. I would just seal it with some rustoleum from Lowes. You can buy it in quart or gallons and or Aerosol spray. that will prevent any damage and wont be so hard to remove when its time to sandblast.

I hope that helps.

I've never used primer under my seam sealers. I usually use 3m Automix, Heavy Bodied seam sealer (don't use "controlled flow" its super runny & will not stay on the underside of the truck). Its a 2 part product and uses a special gun to dispense, so it may not be your best choice. It can be painted in like 30 minutes. There are lots of seam sealers that come in caulk gun type cartridges, they will dry slower, and I don't know if they need primer under. The only single part seam sealer I've used is Wurth, and the rep never mentioned primer first.

For normal repairs, we will seam seal, then scuff with coarse scotchbrite, then undercoat the area with a paintable rubberized undercoating (aerosol can), right over the old paint & repaired area. Most of the time, the undercoating is inside a panel or under the car, so paint is not even applied. This process is approved by insurance companies & manufacturers to restore it to factory specs. Like Shawn said, this is for repaired areas, most cars are not undercoated.

Since this is a stop-gap, and you are planning on redoing it, I'd keep it simple. I wouldn't want to spend a bunch of extra time and money, only to strip it off again. There are some cool paint guns & disposable cups available, but the cost is high and I don't think its worth it, unless you are going for the perfect finish. We use a 3M primer gun w/disposable cup, it worked great applying Chassis Saver to my axles
viewtopic.php?f=5&t=1178

Personally, I'd seam seal, scotch brite, and spray it with some decent spraypaint, or maybe undercoating, and be done with it. If you've exposed a bunch of bare metal you could use a little etch primer to make sure the paint will stick. You'll be good for years.

Chris - I am taking similar approach as you, although just in the engine bay.

I had it sandblasted while the tranny was in (tranny was wrapped and sealed for protection).

Then I decided to take the body off the chassis which means I have a small area of the firewall to do by hand.

I am going to bring it down to bare metal, then primer, then seal the seams.

A couple years from now I will have the entire body refurbished and painted.

you guys are right, iam over thinking this.. what iam going to do is use a etching primer on it.. seam seal it.. then hit with a decent rattle can spray for now until i get ready to paint.. then I will take care of the undercoating.

I have a couple of bottles of etching primer for the POR15 stuff.. so that should work pretty well.

I have read the Fusor 800EZ is a pretty good seam sealer that is not too runny and will move with the metal joints instead of cracking or coming apart.. so I will pick up a few tubes of that.

In the mean time I'm going to hit the frame and suspension with the por15/chassis savor combo and that will be done.

Many of the threads on CB.com are saying if you are down to bare metal you should use some kind of primer first or something similar to por15 (por15 requires an etching primer) directly on metal.. then seam seal it and then paint or undercoat it.. I will probably go this route when I redo my body off.

but what do i know I really am a newbie when it comes to paint and body work

I talked to the guys at work, and if you have a large amount of bare metal (like what Rox has done), and the sealer recommends primer, then use primer. I'd always use an etch primer on bare metal. You can dust the etch on and then follow with regular primer, or just hammer it with the etch primer. Since new body panels have a factory e-coat (kinda a factory primer), or we are fixing already painted panels, there just isn't much bare metal, so we don't worry about it. I'm usually seam sealing over the e-coat, bondo (don't buy Bondo brand bondo, it sucks), or old paint, so we just scuff it and seam seal it.

I took a look at a product we have at the shop 3M 'Fast & Firm' (insert joke here), it is a caulk gun type seam sealer. It does not call for primer (but I'm sure primer wouldn't hurt), and is pretty good stuff. I've only used it as an adhesive (not a seam sealer) to stick intrusion bars to door skins, but its a good seam sealer. We use the 2 part stuff to keep production rolling quicker. We don't want to wait to send things to paint.

So for Rox, I'd prime (etch prime first), then seam seal, then you can reprime and paint. If the seam sealer says its paint ready, then you could skip priming the dryed sealer.

For Chris, assuming you haven't exposed a bunch of metal, you could just scuff & seam seal, then prime & paint. You really can't loose if you do choose to prime before seam sealing, I doubt you'll see a reaction.

When I started the axle thread, I thought the cups were generic, but they aren't. You have to use the 3m cup & collar you listed.

The cup & collar are just a way to attach the actual soft cups to the gun, and are reusable.:
http://www.amazon.com/3M-16001-PPS-Stan ... sbs_auto_4


The soft cup is what actually holds the product, I only used 1 per coat, you can refill them, unless the product gets old/dry:
http://www.amazon.com/3M-16001-PPS-Stan ... sbs_auto_4

Then you need the gun:
http://www.amazon.com/3M-Automotive-.../dp/B003TODXUI

It starts to add up, but if you think you'll do more projects in the future it might be worth it. Since the soft cups allow you to spray upside down, they are great for working under the truck, or on weird shaped products. I bet there are a bunch of guys in this club who could use this kind of thing, and wouldn't mind making a donation to cover the costs of the soft cups, if you loan it out. I bet they'd get used up pretty fast. They are great for priming and super easy clean up (rinse out the gun & toss the soft cup).

They also sell new tips, but if you clean them they last a long time. My painter uses the tips over 20 times before tossing them. The destructions say differently, but that is just 3M trying to sell more tips:
http://www.amazon.com/3M-16611-Accuspra ... auto_img_b

I sprayed the Chassis Saver straight from the can with the gun, no thinner. The Chassis Saver was the consistency of regular primer, so that made us think the 3M primer gun would work good.

Hope I covered everything. Keep shooting questions at me, I can still learn a thing or two from the guys at the shop, and it gives me good questions to ask.

thanks so much, as well.

I am on the fence about buying the spray setup and supplies or just using what I have and foam brush it on... I could use the money else where on the build as it seems it will add up to start buying the spray supplies...

I understand, I wouldn't be able to justify the expense. I'm sure the foam brush will leave you with a perfectly acceptable result. It's not like we are restoring Shelby Mustangs.

I hope to change career paths soon, and I'll have to go back to wrenching on stuff like a regular joe. I have built a sweet set of tools & knowledge to take home with me. But giving up the spray booth, 3 welders, plasma cutter, torches, endless supply of parts & supplies, and access to 2 other guy's tool boxes will be tough.