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Floor rust repair: Am I crazy or is this a good plan?


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This is my daily driver 1974 2002, which I've had for four years. It is parked outside in Portland. No salt but it rains a lot.


I've got a good amount of rust on front driver and passenger pans. I suspect it's from a leaky heater core or from the opening the box sits in. This rust was there when I bought the car, though it is worse now, four years later. I rebuilt the heater box three years ago but I did notice at the time rust around the opening, which I applied POR-15 to and caulked heavily.


The frame rails are dented from a collision over a decade ago (two owners prior to me) but the two separate mechanic inspections said they were fine. The car runs straight with no weird tire wear. From what I can tell, from below, the frame rails do not have structural rust.


Otherwise, the car is in pretty good shape in terms of rust. 10ft paint job. No other apparent rust issues, including shock towers, spare tire well, wheel wells, rocker panels, frame rails, other floor pan sections, body. (From what I can tell visually). Car has 5K on a rebuilt motor, solid interior. Carpet is pretty worn.


I've been all over the forums using search.


How is this for a plan? SANITY CHECK PLEASE


1. Take out seats

2. Take out carpet

3. Take out underlayment (dry ice)

4. Remove rusted metal, grind down adjacent metal (or all metal on entire floor?)

5A. Take a welding class, buy welding stuff, do welding myself, or...

5B. Take it to a body shop for welding

6. Por-15 everything

7. Put in new sound deadening underlayment

8. Put in new carpet


About how many days would you estimate this job? I will need to borrow a friend's garage and buy or rent a second car.


Also what bad things could happen that I haven't thought of?


Other options I'm considering:

- Have a body shop do more of the job or everything (recommendations in Portland?)

- Sell the car in its current state.



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If the rust is pretty much confined to the (relatively) flat sections of the floor pans and you're not going for a correct restoration, you can probably repair sizeable holes in the floor pan without welding and still have a sturdy repair.


First cut the rust back to sound metal, then cutting a piece of sturdy sheet metal to fit the hole with an inch or two overlap.  "Butter" the edge of the hole with wet patch roofing cement (get at Lowes or Home Depot by the gallon), then stick the patch down into the roofing cement.  Take your trusty pop rivet gun, and beginning at one corner, drill holes and set rivets sequentially around the edge.  Doing the four corners first will buckle the metal and not make a tight seal or strong repair.  A rivet every 2-3 inches will make a strong patch so long as the rivets are going into sound, unrusted metal.  The roofing cement will remain flexible and seal the seam between patch and floor.  After the cement has set up for a couple of days, paint the patch and back onto the floorpan with your choice of anti-rust paint.  Sherwin-Williams makes a very good industrial red oxide primer (made for ships and steel bridges) that has proven to work well on our salt-laden roads.  


I thusly repaired a Honda CRX with essentially no driver's side floorboard and it stayed nice and dry (and no more rust) for the entire winter and still looked good when I sold it the following year.  




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Good plan. In your case I would take 5B unless you need/want to buy a welder and invest some time and money for the future jobs. Do everything else yourself but let shop or somebody with welder and experience do the metal replacing. It shouldn't be more than half day job for someone with the tools and know-how. Most or maybe everything you can do without putting the car out of use. Seat is just four bolts so you can easily put it back and drive home when carpet is removed and continue next day.


Removing seats, center console, carpet - few hours. Cleaning sound deadening, inspecting for rust... - few more hours, maybe one full day (don't know how effective dry ice method is). Then prepping and painting after welded - again few hours. And mounting sound insulation and new carpet - few hours x2. Seats and console back another few hours. People work so differently that it's impossible to say how many days it takes for someone else, probably couldn't guess it right if I was doing it myself.  


Worst that can happen is burn the car while welding, or damaging glass or interior with sparks.



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I got my car in a state right before step 4 - tar removal. 


Tar removal goes pretty quick and its kind of fun banging away after freezing it.  I forgot some under the rear seats and did not get the tunnel done, so there will be two rounds.


I chose to go the 5a route, except "welding class" is "watch a boat load of youtube videos."  Its been slow going with a few false starts, but I'm on track to fix it.  Welding seems to be 90% preparation, just like painting.  You can weld in the patch in about 5 minutes, but it could take you 3 days of solid work getting that first patch ready.  I'm still not ready, life has gotten in the way, but I had never done any metal work before, so even just trying to cut the metal out of the floor pan and then cut out the patch was a real learning experience.  I still have to get back at it and trim up the initial hole and patch to fit each other.  That will take me hours and frustrate the heck out of me, and that's just trimming and fitting.  An experienced guy could probably do the whole job in a half hour start to finish.


I like doing the work though, so to me its worth it.  And I guess that's what's going to make the decision for you:  if you like a challenge and sense of accomplishment, do it yourself.  If you want it done right and quick then have a pro do it.




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Your rust doesn't look that invasive. Did you explore with a sharp tool to see if it is completely rotted through--your message implies the carpet is still installed. Maybe treatment with wire brush and rust converter would suffice. You could work on each side separately to avoid serious downtime. If you intend to keep the car then I would advise using welded patches for the repair (which is rather difficult with thin sheet metal). I am not a big fan of POR-15 but recommend using an epoxy primer instead.

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Thanks for all the replies! This is helpful and I'm feeling more confident about what I could do.


1. It is definitely rotted through, I could see another piece of loose sheet metal that a previous owner must have put on top, maybe with adhesive.


2. I can't see around having to get a separate car. With my work and parenting schedule I think this job will take 2-3 months. Maybe I could buy and sell an old beater.


3. Any advice on how to find a good auto welder in Portland, OR? Restoration shop? From what I've read I need to find someone to do butt TIG welding. I don't think I want to buy all the gear and I don't really have a place to keep it after the job.

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