What gauge steel?

[gt crazy]

So i've been planning on welding new floorboards into my car. My passanger side has been cut out, grinded, and sanded. Its ready for the steal to be welded in. The thing is I don't know what gauge steel should I put in there, because im worried if i go to fat I will burn through my steel on the car. And if I go to small I will burn through the new steel. I also don't know what kind of steel I should put in there. Any suggestions? Advise?

[GTJIM]

GT bodies are quite thin steel - the floorboards about 20 gauge and the panels closer to 22 gauge.

If possible try and use 'Zyntec' which is electro-plated with Zinc and used mainly in air conditioning ducts for buildings. NOTE: NOT 'galvanised' iron but instead has a smooth grey finish instead of the 'crystal' look of galvanised sheet. A bit harder to weld than raw steel sheet but if you disc sand the Zinc coating off the edges to be welded it is easier - just spray with a Zinc-rich primer soon after welding to stop rusting (something like "Cold Galv" which is available in spray cans with several colours).

[opelspyder]

20 Gauge is a good size to use, and is closest to the metal used in the GT. To save money you can buy a sheet of Hot rolled, just ask for it to be "pickled" which is a process of removing the scale after manufacturing. I don't recommend the coated metal, due to the welding problems. Coat it after you installed it..... There was a guy that swore his floors were 14 gauge. I'm sorry, but there are only a few pieces that are that thick, and they are for structural supports. I think the original battery tray is about that thick too.
Keith

[gt crazy]

explain this "pickle" scalled stuff. I dont quite understand

[RallyBob]

explain this "pickle" scalled stuff. I dont quite understand

What Keith is referring to as 'pickling' is a chemical dip (often alkaline or acid) to remove the 'scale' that is left on hot-rolled steel when it is manufactured. The 'scale' makes welding tougher, and it also generally peels later on. If it peels, then so does your primer and paint!

The other alternative is to order cold-rolled steel. It is bare metal, usually just lightly oiled for rust protection. In a humid climate, once you remove the protective oil the metal rusts extremely quickly...at my shop it will rust overnight wherever my hands touched the bare metal. So leave the oil on until you're ready to weld, prime, and paint!

Bob

[Johnvan]

I use cold rolled low carbon mild steel for a number of reasons: #1 It is the same steel the Opel was built with. #2 cold rolled steel is more pliable and can be shaped easier. #3 Low carbon steel is softer ( High carbon would be an axe blade or spring etc.). #4 A clean surface with less impurities. #5 Good welding characteristics.

I don't use "satin finish" zinc coated sheet because I have found from experience that even with proper preparation it tends to rust out quickly. In my opinion of the "satin finish" steel I used this is due to a lower carbon level and a poor quality steel with more impurities in the metal.

20 gauge sheet metal would be good for the Opel. You can get "autobody" sheet metal at your local body and paint supplier but the quality is sometimes inferior. I would recommend you purchase the metal at an industrial steel supplier in your region. The metal would be available in 4' X 8' sheets or larger and can be cut smaller by them to suit your needs.

John

[kwilford]

I don't use "satin finish" zinc coated sheet because I have found from experience that even with proper preparation it tends to rust out quickly. In my opinion of the "satin finish" steel I used this is due to a lower carbon level and a poor quality steel with more impurities in the metal.

John, if the satin finish was of decent grade steel, do you think it would do better than cold roll? I have used both, and the satin finish sheet stays rust-free for much longer than the cold roll while sitting in my garage. Granted, Calgary is inherently MUCH lower humidity (except for this week!) than Quebec, but over a few weeks, the bare cold roll still formed a bit of rust while the satin finish metal has stayed rust-free for months, even years. I think that the zinc, while pretty thin, at least provided some inherent corrosion protection in the absence of proper paint.

I have used a combination of satin finish and cold rolled, most in 22 gauge which is exactly (by micrometer) the thickness of the Opel body panel sheet metal. Structural metal, such as inner rocker panels, floor rails and such, measured closer to 20 gauge. I believe that the frame rails are closer to 16 or even 10 gauge, but if you're repairing those, the car has bigger problems. Floor panels (the flat portions) were exactly 22 gauge.

I bought most of my sheet metal from the local Princess Auto. It came in 2'x4' sheets and the price was quite a bit better than the so-called "body repair panels" from the auto supply stores (IIRC, $22CAD for the cold roll, $28CAD for the satin), although not as cheap as at the metal supply stores. But they aren't open weekends and evenings, and are a longer drive. I have used one sheet of the cold roll, and three (!!) of the satin finish. And about thirty pounds of 0.024" MIG wire, four (!!!!) bottles of MIG shield gas, and more hours than my wife cares to remember over this past winter.

I used the satin finish where I wasn't certain to get a decent coat of protective paint in behind, such as rocker panels and fender arches. I made sure to spray paint all hidden surfaces (hidden after they were closed up) and the inside of repair panels with "weld through zinc rich primer" spray paint. I used the cold roll for the floor panel and the top of the fenders, where I was certain to get good film coverage with the self-etching epoxy primer I am painting after the final finish sand-blast. This blast will probably remove the satin finish on the external surfaces, but the inside surfaces will still have both the zinc finish and the zinc-rich primer spray. As much as possible, I intend on getting the self-etching epoxy primer sprayed into the inner areas, which should be fairly possible what with my GT being on a rotisserie.

If you are interested, I posted a number of photos of my sheet metal work over this past winter at
kwilford Gallery - Opel Photo Gallery
starting at
Rotisserie 2007 - Opel Photo Gallery
and ending (for now) at
MIG Welding Bodywork 2008 - Opel Photo Gallery

[Johnvan]

John, if the satin finish was of decent grade steel, do you think it would do better than cold roll? I have used both, and the satin finish sheet stays rust-free for much longer than the cold roll while sitting in my garage.......

Your metal could be of a higher grade then was available here and looking at the extensive amount of cleaning the welds and surface preparation along with priming you likely won't have a problem. But it may prove to be more difficult for a less experienced person. Zinc coated metals will outlast uncoated sheet in it's natural state if open to the elements.
All metals come in different grades and quality based on the producer and the quality of steel as well as the alloy can be altered to provide different properties. Satin finish sheet is still cold roll with a zinc coating. Satin and galvanized metals are generally joined by riveting, soft soldering , bolting and seaming as in furnace ducts. Welding is usually not recommended as the zinc coating has a lower melting point and boiling point than mild steel which defeats it's purpose and creates very unhealthy fumes and can penetrate the pores of the "weld area" creating a premature rust condition. Zinc is a non-ferrous or "dissimilar" metal and can set up a chemical reaction with the heated ferrous mild steel. Similar to the reaction at the welds on panels which have been braze welded." Please Note" The auto manufacturers use zinc coated panels in high rust areas such as rocker panels with arguable results and hold up well if properly treated but it is always a disputed application.

I have found 20 guage to be a good "multipurpose" guage to use as it will hold it's form well with less distortion during welding but 22 guage would be fine as well. The satin sheet I used would bend easier but would "work harden" and crack quicker when forming which was another reason I went to the uncoated sheet. I prefer to make rockers out of 18 guage as the variation in thickness is not noticable and it provides better strength.

Your work looks great! John

[CharlesEvans]

You didn't mention which car you have. Ford would require 16 gauge cold roll steel. I just had mine done a few weeks ago.