How to rust proof new welded in parts??
 

I am finally getting serious about my '64 SC. I am repairing (rather than restoring) the car. The body is in remarkably good shape. The only serious rust I found was a small area through the left front strut, into the inside of the wheel well and into the pedal area behind the floor board. I have cut out all the serious rust and will need to replace about a 9" square piece of the floor to the left of the pedal assembly, some of the inside of the wheel well and the left front strut. I want to seal and eliminate future rust. I have solid, but surface rusted metal around the areas I have removed so I will have a mix of bright new metal and surface rusted original metal to paint. I want to paint (or otherwise seal) the new metal that will be covered when I install the front strut. I also want to seal the inside of the strut.

I have a couple specific questions:
1) How should I treat the mix of new and old steel? It is hidden, so I am not terribly concerned about how it looks, but I want good rust proofing. Rust encapsulating paint over the rusty parts, but how should I treat the adjacent new steel?

2) How should I treat the repair piece behind the strut and the inside of the "box" of the strut? It will be new steel, but once I weld on the strut, it will be enclosed and hidden. I really want to get it sealed, but am not sure if I should paint the inside then weld the part on or do the welding then try to get paint into the strut.

3) I plan to overlap and plug weld the new metal to the old and would really like to treat the space between the two metals where they overlap.
I plan to add undercoat over the paint on all the exposed parts, but really don't want rust forming in the hidden areas on the new steel.

Thanks in advance for you wisdom.

I used a high quality copper type weld thru primer (German and expensive) on metal that was going to get very hot from nearby welding. I believe I sprayed in inner parts of the front struts with this stuff. Rust preventative paints such as POR15 are of course good for old metal with surface rust. New metal can have either an epoxy primer of self etching primer sprayed on them. Most of the undercarriage of my 356A got painted with an epoxy primer then an industrial metal paint from General Paint. The car lives a pampered life now and I am sure it will never rust again.

Also, make sure you cut the bad metal back to good solid metal or you will never get the patch welded in properly.

True that! I'm getting there. I like the idea of the weld through primer. Do you think that will adequately seal the inside of the strut? I was always told primer doesn't really seal - just provides "tooth" for the top coat to adhere to. I suppose anything is better than nothing. I'll cover anything exposed with good paint + undercoat. How about painting the box part of the strut - masking off the flanges for the weld - and using the weld through primer on the flanges?

I'm not ready to start welding yet, but am getting closer to the plan.

Thanks for your help.

Pictures
 

I finally got an image editor on my shop Linux machine so I can resize my pictures.
Here is what it looked like
http://forums.pelicanparts.com/uploa...1349733162.jpg

Here it is after cutting out the rust and cleaning up the area

http://forums.pelicanparts.com/uploa...1349733300.jpg

An epoxy primer/sealer will seal it forever. The only issue is that if it is close enough to the weld it will get burned off. You could spray the inside of the strut with epoxy primer and just paint the welding flange with weld thru primer.

You are doing a great job, I learned to weld 20 years ago on a B sunroof coupe restoration.

Your patch work looks very neat, i would acid etch prime the cleaned up area and the patch pieces, place the patch pieces over the prepped area and using a scribe tool scratch the outline. You can use a dremal to clean to bare (remove just enough primer) metal the edge of your patch piece and the area of the car which will receive the bead of weld.

You have to realize the heat will burn off some primer and there is really no sense losing sleep over that. Clean it up and re prime what you can see.
Inside it will last just fine when properly maintained as i am sure you will. You cannot let it make you nuts, it will be fine.

You can also buy special vise grip flange creating tool which will create an offset on the body of the car where metal replacement is to take place. It offsets the approxiamate sheet metal thickness to accept the patch piece and allow it to lay flush.

i think i bought mine thru Eastwood.

Best of luck

SEM 39783 Weld-Thru Primer

Less than $20 with my discount from Napa Auto Parts. It was actually cheaper than the "Napa" brand.

Yeah I ended up using a half a dozen vise grip type clamps doing the underside of my 356. An assortment of these are indispensable.

I hava a plan
 

Thanks for all your replies.

My plan will be to cut and fit all the patch pieces and the left strut, figure out where the welds will be (I have an air Flange/Punch tool and use it were appropriate), use weld through primer where the laps will be and weld in the patches. Since it is not the body, I'll either weld the laps along the edges or punch holes and plug weld. I'll use the POR15 Prep & Ready on all the new steel and paint everywhere except where the welds will be with POR15. I'll prep and paint the inside of the strut the same way, use weld through primer on the "flanges" of the strut and plug weld it on. Now, with it all together, I'll prep then POR15 the new steel and extend the POR15 onto the surface rusted metal.

In spite of having painted the inside of the strut, I'll drill a small hole and spray something like Waxoyl into it.

There is some surface rust on the inside of the fenders and the floor so I'll scape back the existing undercoating to shiny metal (I have done a little of that already and there IS shiny metal under much of the undercoat http://forums.pelicanparts.com/suppo...s/beerchug.gif). I'll POR15 all that and follow it with undercoating.

Work will keep my busy for a couple weeks, but I'll ad pics as I progress.

Thanks again,