I'm finally getting into replacing the rockers and floor. There is surface rust on a few spots around the doors and the quarter panels. After I remove the paint/rust with a wire wheel, the metal looks good with a few pits.

There's also surface rust on the front sheet metal and when I clean that there are just very minor pits. I don't want to replace those panels if it's not necessary but I'm not a metal expert.

I'm wondering at what point do you cut those pieces out and repair vs. cleaning and putting POR-15 or some other rust inhibitor?

Thanks

I'm wondering at what point do you cut those pieces out and repair vs. cleaning and putting POR-15 or some other rust inhibitor?

Thanks

I usually go by what the structural integrity of the remaining metal structure is.
If there is enough rigidity and strength in the metal to allow for some minor filling of the pitting and not effect it's future ability to support the structure, then I thoughly clean the area and use a direct to metal filler - like Metal to Metal (Evercoat) to skim coat and then smooth the area prior to primer/sealer.
If there is noticable perforation/'pin-holing' in the metal and there is any 'give' or deflection when pressing on the surface in a normal manner - then I cut that part out and replace with a patch or panel to restore the needed strength to the structure.

Minor surface roughness, from mild surface rusting, can usually be smoothed by thoughly cleaning the area with a good etch cleaner (like a 'posphoric acid' product such as "Ospho" - www.ospho.com - ) and a 'ScotchBrite' pad and then rinsed prior to a Epoxy or Etch Primer coat and then a '2K' build-up and sanded smooth prior to sealing and topcoat.
If the "surface rust" is really rough, then a skim coat of filler over the entire area may be necessary to get the smooth surface you are after - only you can access this as you get the rust off and see what's underneath.

I have used some of the 'POR-15' products available in their "trunk and floor pan" repair kit to do some minor filling and bridging of some rusted out areas on a couple vehicles. These were small. non-cosmetic areas under seats and in the toe-kick areas on vehicles where no replacement or donor panels were available.
The 'kits' worked well, with the exception of the fiberglass matting they supply, it is way to thick and dense. I use a much lighter grade glass cloth and ripped the edges rather than cut them as instructed in the 'kit'. You can get the lighter grade cloths from any fiberglass supply outlet - I got it from a local "TAP" plastics store.
Use of the 'lighter' wieght cloth/mat allows you to tailor small pieces for a given area, and to build a couple layers if necessary for some small added strength, while not building up alot of thickness. It also produces a very smooth surface that overcoats easily, unlike the thicker stuff in the kit.

This is based on my normal procedures to get an older car or panel ready for prime/paint - but, I'm just a 'hobbiest'.
Hope some of the real 'autobody pro's will chime-in on this tread and add specifics as they may apply in your case.

John

For things like rockers and floors, you have to determine if the pitting is just surface pitting or has caused the metal to weaken. The floor is easy to spot as you can see both sides and clean it. If there are no large areas of thinning metal, I would consider cleaning and treating with POR15. Thats what I 'm doing for the floor.

If you have areas to replace, the floor is a good place to learn how to cut, patch, and weld in sheet metal. You can buy replacement floor panels and cut patches out where you need them.

For the rockers, you need to be sure that they are not rusting from the inside or you will fixing it again very soon. Better to take the time to do it right and have to do it over again later.

I second John's vote for Metal to Metal filler. Good stuff.

The way I assess this kind of rust is to first consider the original thickness of the panel in question. A 14- or 16-gage panel with scale is a lot less of a concern than thinner stuff.

Then, look at where it is. Is it a major structural joint or in an area of major stress?

Then, start poking at it. Can't really tell with just a finger or a screw driver; I use a light body pick hammer and tap at the affected area. I don't haul off and hit it full swing, but you can't be timid either. If it stands up, or dents a little, and you don't sink the pick or hear a bunch of scale falling on the opposite side (like in a rocker), you're probably good to go.

An example would be the top of the cowl where the seal sits and collects crud and causes surface rust. I cleaned mine off, and it was pretty pitted but was sound and not in a crucial area. I primed, Metal to Metal skimmed it, sanded and painted and it's good as new (except it's missing the hidden VIN).

Inspect those rockers real well. On a vert, they are critical! The ones on my 68 were gone to the point I had to weld in frame connectors to make up for the rocker rot (this was before they made new vert rockers). Pull the inspection plugs in the wheel well and get a light, small mirror, and/or one of those lighted bore scopes. The ones on the 69 were solid, so I just cleaned out the junk and blew a bunch of waxy anti rust into all three compartments from both the front and rear of the rockers.

Thanks for the comments. The rockers are toast .. whats left of them anyway. And the floor pans aren't much better. I was asking mainly for the quarters, cowl, front fenders ... I want to try and retain as much original metal as I can but also want to be sure I'm not causing problems down the road.

Is there a good way to get inside the cowl(? - under windshield) and see if any damage was done there. I can see there is surface rust but it's a little tricky to get in there and clean it out.