Restarting a butt weld after an interrupted job.... Preparation?

  1. MWAD7 New Member

    S Queensferry, Scotland
    Good morning!

    One of they key future projects that is driving me to learn to weld is the likely restoration/repair of an ex-military trailer for a Land Rover. The bodies of these trailers are sheet steel and they tend to corrode and rot through where the sides meet the floor if they are allowed to fill with water.

    So, in theory, there will be plenty of cutting out of flat panel sections and welding new metal in. Panel thickness is relatively generous for automotive work (around 2mm for the floor, I understand).

    Anyway, when I eventually get around to this, I will have to do the work outside and I guess it’s quite likely that it won’t always be possible to finish a section in one go.

    So - let’s say you’ve got halfway through welding a new section in and then run out of time on a Sunday evening - how would you prepare the remaining joint for welding when you get back to it a week later after it has been rained on a few times (I’m on the coast too....)

    Aside from being a realistic future scenario I’ll face, it’s something I can easily practice over the winter and have the luxury of being able to destructively test practice pieces...

  2. Just make sure the joint is rust free, particularly on the mating faces, a rotary wire bush and sander will probably suffice
  3. Instructor_Nige Member

    Hi MWAD7
    Your question appears to ask how to restart a weld run after returning to it after a break.. The good news is MIG is the easiest to restart and as you are not welding a pressurised container etc, aesthetics are probably the most important factor.

    Any weld that is left in a damp or wet environment will begin to rust quite quickly. So ensure that you clean the end of the weld you left before continuing your welding. start your weld a little in front of the last weld, pull the pool back to join the old weld before continuing with your run, this will reduce unsightly bumps where too much stock is sat on top of the previous weld. we could go into key holing but not necessary for what you are doing. there is not much else to worry about... however have you considered other factors?

    You mention doing the welding outdoors, you're on the coast.. this means wind.. MIG welders do not like wind, even a light breeze can cause porosity in your welds.. You should consider ways to shield the work area from the wind... another alternative is to use flux core wire instead of gas.. but the welding technique is very different. Many people give up on flux core because they weld like they would with standard MIG, this is incorrect as you must weld almost in same way you would with a stick welder by pulling the weld and allowing the flux to coat the weld pool. you even chip off the slag in the same way you do with stick welding.. think of flux core as a continuously wire fed stick welder and you will get the idea.. also many welders need to have the polarity reversed for flux core welding, another common mistake..

    My advice from personal experience would be gas MIG and shield the area with tarpaulin, a lot less bother and far more enjoyable job.. also cover the welded areas with a sheet before leaving until next time to reduce surface contamination.

    backpurge likes this.
  4. Ed B

    Ed B Member

    Hi. I dont know much about welding, as just reading up on it whilst looking for a suitable mig welder - but maybe you could apply some of this

    ACF-50 which is really good for stopping bare metal rusting. Of course you might need to clean that off before you start again, or maybe it will just burn off? Anyone know the answer to that?
  5. Shedendman

    Shedendman Member

    east sussex