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
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