Heavily rusted bumper, the outside is fine. What is the best way to build up the heavily rusted and pitted area?Click to view attachment

Get some navel jelly and soak it. Keep repeating until clean as possible. Lots of rust preventative paints out there.

Remove the rust first, wire brush on a power drill, then phosphoric acid soak till it turns black, rinse with water very well, than seal with por-15

Could it be rechromed and look decent?

Unlikely that it could be brought back from that heavy pitting. Or if possible not economically feasible as you can buy a new one for not too much money. Understand the motivation but as long as it looks good on outside and you take steps above you will be fine if keeping original.

Guess it depends on what the money side looks like.

"Build it up" as far as I know there is no such product. You can remove the rust with one of several methods, many mentioned previously

Here’s my guess. There is so much rust that I’d be surprised if it’s not gone through the metal and is being hidden by the chrome on the other side. I think blasting the corrosion will reveal Swiss cheesed metal. Of course I’m just guessing but it would be typical.

The money side looks good. It is going to be painted.

Throw that thing back in the surf

I would actually do the phospho wire brush step multiple times until the rust color no longer appears when wire brushing it. This rust looks deep.

I would use a brass wheel in my drill motor. If ok, I'll post some pictures of a rough early rear I have. Paint to match the red one on the front? Look in to Mar-Hyde for a rust converter product.

sem rust sheild

If your plan is to paint, just sandblast it.
Standard metal prep, fill, paint after

Try to poke an awl through from either side before wasting any work time. Start with the worst spot. I bet you will find all the steel is now rust.

For painted bumpers, you can treat it like any sheet metal. Cut out the bad, weld in some new, shape, and finish.

The chrome finish one I have is the early version with the sharp edges around the plate. It’s rough. Perhaps better sold as a paintable early core as is? I have few bumpers that need new homes. This is not an ad.

Please follow up when you go at it. Would love to see this work out for you.

I just ran across the following video. It may help if the rust is not too serious.

https://classicmotorsports.com/video/video-..._eid=2ed9ec98ea