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Joining Galvanized Steel Sheet

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  • Joining Galvanized Steel Sheet

    Hello all,
    I need to reduild the flashing around the chimney of my house and am looking for some advice... It looks like Galvanized steel sheet is most common.
    I'll be building a saddle out of galvanized steel sheet (I'm thinking 20 or 22-gauge). Here's a pic of a typical saddle:

    I'm looking for advice in joining the material... I have a TIG, but from my research it seems that soldering is probably the way to go for a number of reasons, not the least of which is the fumes created from welding the galvanized steel.

    #1: Should I be looking to use a different material given the fact that I have the ability to TIG it together? Is Galvanized generally used because of it's low cost and high availability? I admit I'm not the best at TIG welding thin sheet, but I could probably make it work with a little practice. Stainless sheet is a little bit expensive, but I wouldn't need much if that's the way to go.

    #2: If I do decide that galvanized is the way to go... Does anyone have any experience they could share about joining galvanized steel sheet? What type of solder, flux, etc?
    Could I use a MAPP gas torch or would a large soldering iron or coppers be better?
    Many thanks.

  • #2
    Has lead flashing gone out of style, or been banned? Galvanized won't last all that long.

    But if you do want to use galvanized, regular 50-50 solder and tinner's fluid (acid flux) will do the job.
    Try to make a living, not a killing. -- Utah Phillips
    Don't believe everything you know. -- Bumper sticker
    Everybody is ignorant, only on different subjects. -- Will Rogers
    There are lots of people who mistake their imagination for their memory. - Josh Billings
    Law of Logical Argument - Anything is possible if you don't know what you are talking about.
    Don't own anything you have to feed or paint. - Hood River Blackie


    • #3
      Last two chimneys I did I just framed a small saddle (about twice the size of that in your picture) from lumber and plywood. I flashed to that and applied roofing. One is 23 yrs old the other just 1 year. both doing well, so far.
      Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
      ~Practitioner of the Electromechanical Arts~


      • #4
        A good soldering job on galvanised steel will last as long as the steel. In the "old days" all roof sheet metal work was soldered copper and it would easily last 50 to 70 years (galvanised won't last that long but coppers is $$$$$) if done right.
        The shortest distance between two points is a circle of infinite diameter.

        Bluewater Model Engineering Society at

        Southwestern Ontario. Canada


        • #5
          Don't go anywhere NEAR zinc (galv) with a TIG. If nothing else, you're gonna spend some hours or $$$ cleaning/replacing your torch.
          TIG dc electrode positive has to be seen to be believed when it comes to sucking zinc, even when I thought I'd prepped the metal inches back from the HAZ.
          Just got my head together
          now my body's falling apart


          • #6
            Solder it. A propane bottle torch and some 50/50 lead solder with zinc chloride flux brushed on will make very quick work of it. You aren't building a piano.
            Free software for calculating bolt circles and similar: Click Here


            • #7
              I would use copper and tig it.It will cost more,but it will be the last one you will need.
              I just need one more tool,just one!


              • #8
                You can also seam and crimp it. I think it's called a "Pittsburg seam" by sheet metal men.


                • #9
                  Another vote for copper here.


                  • #10

                    galvanized is very cheap, and does last a lot longer then you would expect, it also retards growth of moss etc on the roof.

                    copper is not cheap, but lasts almost forever, drawbacks are that it is known to produce green streaks on a roof and with time, the eaves of the house.

                    In my opinion regular 50/50 60/40 with decent prep is perfect, anything higther temp will burn off the zink and eliminate any advantage of using the galvanized.

                    I have done a lot of roofs, and generally folded lap seam them, no worry about solder etc. Depends a lot on expected conditions, in the snow belt, solder is preferable, to prevent snow build up from allowing the melt to flow through.

                    Make sure you have suitable support under the ridge on it though, it's a favored position to stand on when doing anything to the chimney, and for re-roofing etc that area serves as a perfect catch-all for tools, lunch boxes, shingles etc. A simple ridge of 1x with V legs provides a lot of support.



                    • #11

                      OK; something more than an amature tin basher here....Although I mostly do HVAC work....
                      What you show there is called a Cricket flashing. Can be stick-built as well, as someone else said.
                      As far as materials, for lower cost & moderate life span, go with galvanized. DO NOT bother to try & weld galv. by any process. The fumes are deadly (seriously, with out adequate ventilation....) and will contaminate a TIG tungsten....Soldering is so much easier...use 50-50 and flux, as others have said. A low grade heat source like a cheap propane torch will make burning away the Galv. plating harder. Also don't over look spot welding. I join most bits of custom made fittings using my ancient spot welder (Lincoln). Harbour Fright & others sell a Chicom copy that even works...Paint your joints after soldering with Galvalume paint for better corrosion resistance.
                      Seams are another option, Standing seams can be water tight, Pitts seams not as easy....
                      Copper is the Rolls-Royce of roofing mat'l. Use it if you can get/afford it. It is readily joined by soldering (if clean & fluxed).
                      Caulk all of your nail/screw holes, counter flashings, regelets etc. Remember that flashings get hot & move. That's why you use expansion joints, counter flashings, standing seams (that may not seem water-tight), storm collars, etc. to allow for expansion. Think of roofing & flashing as fitting together as a system, like ducks feathers or fish scales. That's how they keep the rain out.
                      There are a few thoughts, anyhow....


                      • #12
                        Yep, a sloped roof needn't be watertight. Water doesn't run uphill. The flashings should be installed so that any place the water runs off it is onto another surface that eventually directs it off the roof. The overlaps on the large three flue chimney I have aren't sealed at all and water never comes in. All you need is sufficient overlap to prevent melting snow from reaching the level that it runs over the top of the flashing underneath the lap.
                        Free software for calculating bolt circles and similar: Click Here


                        • #13
                          Never heard of using galvanised sheet for flashing work here in the UK, its lead or zinc sheet.
                          The lead is joined by 'burning' joining by welding lead fillet, the zinc by soldering.
                          Lead flashing will last the longest but zinc will last upto 100 years as on my roof, slate with zinc flashing.
                          Although around the chimney its is lead

                          I have tools I don't know how to use!!


                          • #14
                            Joining Galvanised steel sheet

                            Basically, the other answers are quite authoritively correct.
                            Copper is what every self respecting building in " Sound of Music" is done.
                            Lead is what every cathedral in England has but the United Can Company has tin or terne plate.

                            What has BMW and the rest of modern cars got? Galvanised metal!
                            Digressing, I recall a body repair film on how " Beemers" were repaired after crashing---- repeatedly. If you recall, car bodies are spot welded and even the number of welds in a section are counted. When each spot is created, the two plates are fused together- after the zinc is melted, forced away so that the steel can join---- and then flows back to seal the rustproofing.

                            So, repairs, which you are doing, should be stitch welded with a Mig and not a Tig.

                            I was mulling over the answer and asked myself " What if the guy hasn't got a stitch facility on his Mig?" One can use a cheaper Mig to do a plug or sort of spot weld.

                            Does this help?



                            • #15
                              I've done a lot of galvanized with TIG using silicon bronze filler rod. It isn't
                              really welding, more like soldering, but it makes a fairly strong joint. Just keep
                              the heat down and stay away from the fumes.