BEST way to patch floorboards?

[DirtyWhite77]

The lowest sections of all 4 floorboards in my 1977 TA are rotted out. Only the 12”x12 area you rest your feet. The tunnel, seat mounting areas, rockers and firewall are all really solid so I don’t want or need to do a whole floor. It’s pretty much the areas right around all the body plugs. I’m a welder by trade although not anything to do with autobody. I have the equipment to attach the new panels in any conceivable way. I just can’t decide on the best way to go about doing it. I see two ways really. I have new panels for the front and I’ll buy some for the rear when the time comes so the patches will perfectly match what’s still there.


1.    Butt weld it all the way around with easy grind wire as to not create to much heat when grinding. Paint both sides. All welding done from the top side of the car.


2. Cut the the new panel 1-1.5” oversized and drill the edges every 3/4-1” for spot welds. Then weld 1-2” on both sides of all 4 corners. All welding done from the top side of the car. Weld through primer on the floor and bottom of the new panel before assembly. Paint and then caulk neatly smeared around the edges of the patch from the top.

If anyone has any other method or idea I’d love to hear them. I see advantages to both. I’m looking for the strongest long lasting approach. Time or work involved doesn’t sway me much. I know once carpet is down it will be invisible and keeping water out is how to keep them from rusting. I don’t plan on selling my car anytime I just want the repair to be done right not rednecked in.

[roadking77]

If youre a welder by trade I would seek to ask you for advice  LOL
Im a carpenter and by no means a welder but I did mine with the butt weld method you described. I cut the patch to size, laid it over the floor traced around it and cut the bad out. I used body weld clamps and mig welded it in place from the top. Ground the weld down with a flap wheel, any misses and I touched it back up. I went over the bottom side with some metal to metal filler before paint and it came out looking like nothing ever happened. Several years down the road it still looks great! 

I have heard not to lap the patch and weld as it will create an area for moisture, hence more rust.

I dont know if what I did was right but it worked for me.

[ryeguy2006a]

If you are seeking the option that will look most original and less likely for rust to come back, you will want to us butt welds.

One thing that I'll say is that it takes forever to butt weld 4 complete floor pan sections, grind them smooth and paint. When I was first doing my car, it came with the patch panels already so it seemed like a no brianer to just use what I had. However, from a time standpoint, it took so long prepping, welding, grinding, re-welding, grinding, painting, etc... I would have been so much more time ahead buying and installing a full floor pan with just fitting the pan and spot welding. I also believe at the end of the day, that is a much better repair since the metal is all new and there isn't a chance of contamination in the middle of one of your butt welds that could start rusting.

Just my 2 cents. If I had to do mine all over again, I would pay the extra money for a full floor and have more time.

[roadking77]

Ryan has a valid point. My 77 needed, dr and pass fronts, and both rears! Toe panels were bad as well. I spent a lot of time replacing that stuff. My neighbor at the time restored cars and told me to replace the entire floor and be done with it. My first time with floor repair and I was too intimidated to do so. So I did one piece at a time. It all came out fine and I dont worry about future problems but for all I had to do a full floor would def had been easier. You should brace the body of the car itself before you start cutting out structural metal though.

[DirtyWhite77]

Well it seems like butt welding it is. Pulling the floor may be less welding I guess. I don’t want to scrap the whole rest of my floor though. I don’t need huge patches put in. If I needed a rear seat area or the trans tunnel I’d be a lot more apt to it. Maybe I just need to learn my own lessons. I guess if I get first panel out and hate welding the new one I can stop and look into a whole floor. Really though before I spent $750-800 on a whole floor I could upgrade my welder or get a plasma cutter.

[ryeguy2006a]

The results will be very similar and given that you are a welder by trade knocking out the floors probably won't be bad for you. The thinner metal can be tricky not to get too much heat and burn through. I'm just offering up my experience and what I would do differently. Another thing that is super frustrating is that the aftermarket stampings aren't the same as the original ones, so I spend a lot of time getting them all to fit right so that the ribs all lined up. One trick that I found really handy was after I got one side fitting up nicely I would tack it all into place. Then I would carefully run a jig saw with a metal bit down the area that I wanted to fit up next. It created the perfect width to buzz in the weld and let it fill in nicely.

Another thing to remember is that if you want the repair to look invisible you need to grind the top and bottom sides... So you weld the whole thing then grind top and bottoms. I mean if you enjoy welding, grinding and don't mind spending 3x as long, you can butt weld and it's a good way to save some out of pocket money. However, I would guess that a full floor vs 4 patch panels would be about 3x faster. The lesson that I learned is that; Time = Money. Keep us posted on your results.

[roadking77]

If the patches arent too big you will be fine that way. Being a welder you are already leaps and bounds ahead of where I started. I had to learn to weld and then taught myself along the way. Someone with skills should be able to knock these things out in a good Saturday afternoon.

[FormTA]

Ryan is right though.  MIG welding sheet is an art in itself.  I have 5 welders and weld pretty much every week on something. I always but weld but I lay my patch panel were I want it and sheet screw it in a few places ad then cut it and the panel below it wit the thinnest cut off wheel possible. I have used those clamps Kerry spoke of but usually I spot the panel in a few places, check it's still where I want it and then use my body hamers point to push either the patch panel or the original panel down to make them level (on the same plane). Makes sure you jump around to minimize heat buildup and warpage. I use my cut of wheel on edge to focus the grinding on the welds and then finish with the flap wheel.

I hope this makes sense.

[nUcLeArEnVoY]

You want a seamless repair, butt weld for sure. I would think welding a bead on both the bottom and top and then grinding down the welds would give you the highest quality repair. Depending on how well you grind down the welds, you could theoretically make it look as though there never was any repair at all, especially after primer and paint.

[Wallington]

Why is a welder asking us how to weld?

[ryeguy2006a]

Huge difference welding plate or pipes to welding sheet metal.

[FormTA]

Yes and from TIG, stick, wire to mig. I can do all and have 5 welders in total but if you only know one the others have a big learning curve. Why not ask a group of folks who may have done it?