Rust - how bad is too bad?

[Canoe]

I'm going to come from the other side of this.  Weld in new metal.  If you can't weld, just find someone that can.  Your rust isn't that bad at all.  Just make sure to cut out all the rusty metal in the floor.  As to address Canoe's issues
How are you going to prevent oxygen getting into the metal (which will accelerate any future rusting) when you weld?
Paint it.  On the underside, either paint it, or use the waxoyl/penetrol solution that Canoe uses.
How are you going to avoid blowing (melting) holes through the existing sheet metal when you weld?
If you set the voltage and current correctly to the thickness of the metal you are welding, this won't be an issue.
How are you going to prevent the metal surrounding the welds from becoming brittle?
Cut the metal appropriately so that you are welding good metal to good metal and then paint or rustproof.
How are you going to prevent the weld vs. new sheet metal vs. original sheet metals from rusting at the welds due to dissimilar metals?
??  Dissimilar metals?  If it's steel it's steel.  Paint it or rustproof it underneath. 
If you bolt it, you leave room for a lot of future problems.

There's different types of welding. With some, you have some control, with others much less.
* Painting after you've welding doesn't stop O2 getting to the material while it's hot.
* Heat form welding changes the metallurgy. Unless someone really knows what they're doing, and has the right type of equipment, the surrounding "good" metal becomes brittle.
* steel isn't steel: there are hundred's of types. Your weld rod/wire isn't the same type as your existing metal nor what you add. Why do you think welding fixes rust at the welds? It isn't magic.
* Bolt it? It's as strong as the spot weld, without the issues introduced by welding.
This composite style repair allows you to sidestep all of the negatives possible from welding (ignoring toasting wires or other errors while welding).

[Alcology]

Wow, I didn't mean to pee in your cheerios. 

There's different types of welding. With some, you have some control, with others much less.
So choose the right kind.

* Painting after you've welding doesn't stop O2 getting to the material while it's hot.
No it doesn't.  That's why when it gets cool you prep it and paint it. 

* Heat form welding changes the metallurgy. Unless someone really knows what they're doing, and has the right type of equipment, the surrounding "good" metal becomes brittle.
So find someone who knows what they are doing. 


* steel isn't steel: there are hundred's of types. Your weld rod/wire isn't the same type as your existing metal nor what you add. Why do you think welding fixes rust at the welds? It isn't magic.
It doesn't need to be the exact same.  Someone on here welded in a section of computer case, steel will work with steel for the most part.  And yes, rust does get in there.  That's why you prep it after you weld.


* Bolt it? It's as strong as the spot weld, without the issues introduced by welding.
This composite style repair allows you to sidestep all of the negatives possible from welding (ignoring toasting wires or other errors while welding).
If the floor is already exposed, why not just weld it?  Then you don't have to worry about it.  If you were to put in new steel on the floor, it won't be done with spot welds.  You need to seal it up along the edges.  And any errors can be accounted for by disconnecting the battery and MCU and making sure the arc isn't going to traveling all over your car by setting the electrodes in the right spot. 

I'm not saying your method is wrong, but I am saying that welding might be the better option in this case. 

[Canoe]

Wow, I didn't mean to pee in your cheerios. 

There's different types of welding. With some, you have some control, with others much less.
So choose the right kind.

* Painting after you've welding doesn't stop O2 getting to the material while it's hot.
No it doesn't.  That's why when it gets cool you prep it and paint it. 

* Heat form welding changes the metallurgy. Unless someone really knows what they're doing, and has the right type of equipment, the surrounding "good" metal becomes brittle.
So find someone who knows what they are doing. 

* steel isn't steel: there are hundred's of types. Your weld rod/wire isn't the same type as your existing metal nor what you add. Why do you think welding fixes rust at the welds? It isn't magic.
It doesn't need to be the exact same.  Someone on here welded in a section of computer case, steel will work with steel for the most part.  And yes, rust does get in there.  That's why you prep it after you weld.

* Bolt it? It's as strong as the spot weld, without the issues introduced by welding.
This composite style repair allows you to sidestep all of the negatives possible from welding (ignoring toasting wires or other errors while welding).
If the floor is already exposed, why not just weld it?  Then you don't have to worry about it.  If you were to put in new steel on the floor, it won't be done with spot welds.  You need to seal it up along the edges.  And any errors can be accounted for by disconnecting the battery and MCU and making sure the arc isn't going to traveling all over your car by setting the electrodes in the right spot. 
I'm not saying your method is wrong, but I am saying that welding might be the better option in this case. 

You're obviously unaware of what takes place with welding.
Prepping it and painting it is very nice and stops additional O2 from getting in as long as the seal remains intact. That doesn't stop the oxidation of the weld from the O2 absorbed while welding, further aided by the electron flow of the dissimilar materials. You're closing the barn door too late. And you've already got rust in there; did you do a perfect job of removing it?
Welding does not mean you don't have to worry about it. There's a lot to worry about, and the chance of getting someone who knows and will do a good job is very very slim. Disconnecting the battery doesn't stop the heat from toasting/melting things. Every noted how many stories about someone going and buying a welder, welding and they've melted something or started a fire. Or their pro welder didn't know something was somewhere in their car and did the same.
So how is a novice going to navigate finding a pro who will do an actually informed technically correct job of welding? Pretty slim. And it costs. And you've still got a weld that will rust.
I don't want a repair you're going to have to revisit down the road.

Or you can avoid all of that, and with a low cost method, and you can DIY.

[jim]

Well, MudPuppy, has your question been answered?

[MudPuppy]

Well, yes and no lol. Might just be a bit more confused as to which is best for the long term. Everyone has valid points.

Added a poll just to see.
Like I said - I want this (whatever is done) to be as long term as possible. I do not want to re-visit this anytime soon or if ever (would be nice).
I wouldn't be doing the welding myself. Since I just got a welder and haven't even had a chance to play with it yet, I would not trust myself tackling this. So I would have to find someone to do it. I really need to talk to my cousin, he has his own shop and races his own stock car on the side and see how well his welding capabilities are if I went this route.
Materials I already have on hand - 5/16 stainless steel bolts and nuts, galvanized washers, 24 gauge steel, Bondo-Hair, Penetrol, Klean-Strip's Rust Converter, a few cans of Duplicolor Undercoat spray.

[Alcology]

Yikes, sorry to turn your thread into a pit of nasty.  Good luck with your rust problem, at least you have options.

[MudPuppy]

No worries man. Just glad to see everyone replying and giving me honest options and the how-to steps since this is my first time messing with something like this.
And glad to see that everyone thinks my rust isn't bad lol, I was pretty scared and the more I looked and thought about it the more I worried. So I am relieved to see that it isn't a total loss.

[rollguy]

Although I feel that I am a very competent welder and have very good equipment,  I would still bolt and construction adhesive the metal if it were my car (we have no such thing as rust around here, so no rust repair experience).  I am a total DIYer, and always like to take the easiest route.  Of the two options, the easiest DIY one would be the bolt on, rather than the weld on.   I would also probably use rivets instead of bolts, or at least use rivets to hold the metal on until all the holes are drilled for bolts.  5/16 bolts are a little large in my mind, and I would think more smaller bolts would be better than fewer larger ones.  As far as construction adhesive, polyurethane is the best.  We have the PL around here, but any brand will work.  Also be aware that the only thing that will take Polyurethane construction adhesive out of your cloths, is a pair of scissors!   Being in construction, I have experience with this stuff. 

[MudPuppy]

A lot of y'all are talking about rivets...what kind of rivets (size, and which metal type of rivet is best for this application - figure either stainless steel or mild steel, etc.) and rivet gun (or whatever they are called) do y'all use?
I have a small rivet punch (a handheld thing with the 360 head on it) that I tried to rivet aluminum trim back onto a horse trailer with and it was too weak (or maybe it was me that was too weak lol) to even do that.

[rollguy]

I use "Pop" rivets that are for a 3/16 hole.  They will hold about 1/2" (grip range).   Aluminum would probably be best.   Both the rivets and gun can be bought from most any hardware store or home center.