Welding Patch Panels – Lap or Butt?

Welding Patch Panels – Lap or Butt?


when it comes to rust repair and welding
patch panels one question always arises and that is should I be butt welding
should I cut a patch that fits that hole perfectly and butt weld that or should I
cut a patch that comes close and lap weld it so the idea behind butt welding
a patch panel end is cutting a patch that fits the hole exactly then welding
it solid all the way around grinding it perfectly flat to this surface and
therefore not having to use any filler now the disadvantage is that I see with
butt welding a patch in are these one it takes a super long time to perfectly
match a patch to the hole especially on difficult rust repairs like rockers
fender bottoms quarter panels the bottoms behind wheels upper lips of
quarter panels and so on cab corners okay to cut a patch and have it match
perfectly is that’s pretty difficult the second thing is that after you weld it
absolutely perfect then you’re going to come by and grind those welds completely
flat now grinding welds flat on a small patch like this is fine and you wouldn’t
waste too many grinding wheels but some of the patches that I’ve done are very
large and grinding those welds completely flat as it’s just to me it’s
a waste of grinding disks and time and the third thing I decided that I would
show you exactly what a butt welded patch like this looks like on the back
side so the issues that I have with butt welding
a patch panel are these I took two pieces of metal I butt welded them
together the best I could and I didn’t run a bead I spot welded one two three
one right after the other now it’s solid on this side but do I
know what it looks like on the back side so that when I grind these completely
flat I’m assured that my welds are still thick so I decided that I would I would
do this and show you what the backside of this looks like so here’s the
backside and let me get the camera real close so you can see so again this is
the front side and I’m very confident in my welds you know I’m like oh yeah these
two pieces of metal are completely solid they’re welded together remember this is
on a car I can’t see what’s on the backside now this is what’s on the
backside now you see the this gap right here and there’s pretty good penetration
that’s pretty good penetration but this gap is what scares me if I grind those
welds completely flat on the other side I’m not going to have very much weld
left to stop the salt water from getting into this crack and bubbling and rusting
my paint on the other side so let’s flip this over again and so again if I grind
these completely flat I’m going to have paper-thin welds on this side and
nothing on the backside from the water and salt nothing to keep the water and
salt from getting in this crack and bubbling the paint so the other method is lap welding and
the idea behind that is to cut out all your rust and it doesn’t matter what
your hole looks like it doesn’t matter what the shape is gonna be circular
triangles square whatever then you’re gonna cut a patch that covers it and
you’re gonna lap weld it all the way around just series of spot welds
connected together knock it down and fill it now the advantages of lap
welding are these one is it’s very fast cut the hole out cut the rust out on a
patch that comes close welded up knock it down and fill it
the second advantage is after you weld you don’t have to grind forever on those
welds you just grind down the bad ones or you know the ones that are a little
bit rough just grind it a little bit the sharp edges sandblast or wire wheel the
rest of the crud out knock it down and fill it and then the last thing I like
is this lap welding is very good for intricate patches like cab corners
rockers bottoms of fenders and and door corners and tailgates hoods and all that
kinds of stuff where you have really irregular shapes so for real intricate
rust repair rust repair I like to use the lap welds and then all honesty I do
use a combination of lap welding and butt welding and let me show you what I mean
by that now as I said I use a combination of lap welds in the areas
where you can knock it down and butt welds in the areas where you can’t knock
it down in other words I use lap welds in the open areas where you can actually
knock the metal down below the surface and on the edges I usually use butt
welds so this is a model or an sample that I caught up and let’s just
say I cut the rust out here and this is the edge of let’s say a door or a hood now
there’s always an inner panel there and I took the outer the outer part of it
and just cut it with a die grinder across here this would be the rusty
inner panel that’s left now when you cut a patch you’re just gonna cut it so that
it fits exactly like this let me see if I can get that nice and clear for you
okay so well that’s how it’s gonna fit right there and let me see if I can hold
up okay so this part this part right here
is going to be butt welded because it’s an edge I can’t knock make that edge
crooked I can’t bang this down right here so that I can fill it so I’m gonna
butt weld the edges but while this lap weld this so then I’ll be able to knock
this down all this I’ll just grind this a little bit sandblast it knock it down
just from right here all the way around – right here – right here so all this up
here I’m gonna knock down below the surface with a pointy hammer and fill it
and then these edges I’m gonna butt weld and then grind these wells pretty flat I
don’t like to grind welds real flat because I like to have some meat some
welds on there to really hold that so I’m probably just gonna grind that down
and try to knock it down a little bit and run the filler across there so butt
welds here lap welds here knock this down fill it grind this and fill this
the best I can that’s one example where I use a
combination of both butt welds on the edges lap welds in the open areas now here’s another example of something
you might see on a car this could be the bottom of a quarter panel it could be
the bottom of a door but it’s a very common rust repair so what you have is
is water and salt that gets down in here and it rusts the panel out from the
inside so you cut the rust away and then you die grind this because this panel
might still be good on the inside so try to save that so you cut this out then
you die grind this on the back side you’re also gonna cut because it folds
over so you’re going to die grind this and this and so what your patch will look
like for this is a combination of of lap welding here and butt welding here so I
cut a patch for that and what that’s going to look like is this you’re going
to you know clamp it with a vice grips maybe right here and then weld this side
you can clamp it right on the edge or wherever you can to clamp it some guys
like to put a couple screws in there to hold it but I always use vise grips so
you’re gonna butt weld right here and you’re also gonna butt weld right here
then you’re gonna come up here and you’re gonna you’re gonna lap weld all
this lap weld lap lap lap lap lap knock this down and fill it this you should be
able to grind pretty darn flat pretty flat and because there’s three layers of
metal you can really put some heavy weld right there it can penetrate very deep
and you really don’t have to worry about grinding too much of those welds away
because you are able to use extra heat because there’s three layers of sheet
metal right there I’ll show you there’s one two and three
layers of sheet metal so you’ll really be able to put those those but welts use
a lot of welds right there and not have to worry about grinding them to flat so
butt weld butt weld lap weld knock it down and fill it so when it comes to rust
repair and welding patch panels I like to use a combination of both lap welds
and butt welds I use butt welds on the edges where I can’t knock the welds down
and I use lap welds in the open areas where I can knock the patch down and
fill it so I hope you enjoyed this video on when to use lap welds and when to use
butt welds and if you did don’t forget to subscribe to get my latest videos

12 thoughts on “Welding Patch Panels – Lap or Butt?

  1. Just curious …why didn't you show the back side of a lap weld compared to the back side of the butt weld you showed?

  2. On your lap weld's back side, you have a gap for moisture to sit. Unless you can get some seam sealer on the back, you have a greater chance of rust-out. On butt welds, you always leave a 1 mm gap. Roughly the thickness of your .024 to .030 wire.

  3. Thanks for being realistic and practical. So many candy ass welders showing off with s $5,000 tig welder doing hundreds of hours labor on a $1000 car they are going to destroy drag racing!

  4. interesting note.. when I didn't have a welder if cut rust out of a trunk in a camaro. I ground it clean and used steel pop rivets to hold in on, fiberglass and Eastwood encapsulated it.
    That was 1987 and the car had been outside ever since.
    NO signs of rust and it looks the same as when I did it.
    There is no butt weld that isn't porous to some degree. It doesn't matter how you weld it you better fill it with cosmoline or coat the inside with automatic transmission fluid or something.
    Butt welds are razor thin and just make you feel better. a good lap weld us strong and will outlast a crappy butt weld.
    There is more than one way to skin a cat.
    If you can fix something and it lasts 25 years, nobody can tell you it's wrong.

  5. HI nice video now can you please make a video on filling a panel with a lap weld and how you get filler level thanks again

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