Beginner:Rusted Mercedes Floorboards:weld from above or below?

[Carrameow]

This is my first time welding. I know absolutely nothing about it. I just bought a Hobart Handler 125 Welder 110VAC and I am excited about fixing my floorboards. I'm not even sure how to use the unit yet, but I learn quickly. Floorboards are a good project, because the quality of the weld doesnt matter that much. Wow the small rusted seam that was cracked turned into major cancer! Somewhere I vaguely recall reading that floorboards should be welded from below.
Should I place the metal above the hole or below the hole?
Should I weld from above the hole or below the hole?

http://mywebpages.comcast.net/snow7ice/2.JPG

Here is a view from above.

http://mywebpages.comcast.net/snow7ice/4.JPG
(Believe it or not I am driving this car this way everday to work, the theory being that as long as I have to drive it, the faster I will fix it!)
W123 300D Floorboards:weld from above or below?

I'am a decent mechanic but new to welding.
http://mywebpages.comcast.net/snow7ice/mercedes.html (Here is my Merecedes Site by Richard Chang)

[smithboy]

My dad has a 75 chevy pickup that looks like fred flintstones car. You could stick your feet through the floorboard and run along with it. It's a daily driver also. Until he quit chewing, he just used the hole for tobacco spit. His aim never improved, though.

Seems like welding from above would be easier in a lot of ways...and, safer also. You probably want to use mig not fluxcore. There are a few folks around that have done a lot of body work...I figured they'd posted by now.

[gimpyrobb]

When i did my jeep, I did it from the top. That being said, don't forget to look underneath. I have since been told to make sure you incorperate some plug welds from the bottom and then seal it well.

[timboengineering]

I've welded a few car bodies, so might be able to help. Just cut out as much rust as you can, and when you replace with good leave yourself a 1/2" lip to weld to (bent to a 90). The sills are probably the most important thing to put strength back into. Weld from top or below, I would weld from top to save burns..when you've welded, use a zinc primer and mastic over the joins to stop them rusting again..

[spot]

Hi i am from cornwall where everthing rusts real bad because it is so wet and the
coast is never far a way.
one little gem my Grandad gave to me was " Boy look at the job and times it by ten that how bad it realy is" cut out as much as possable of the rust and then make your patch sit tight to your hole i normaly use some scrap under the patch to hold it in place and tack it all up and then weld it up using sort spot weld to keep the heat down.
hope it some help you kind of have to feel how it going we use a merkle 210me wicth is envently controlabe i am very luck now but spent years getting burnt with the old stuff we had
alot of it is prep and seting about the job in the wright way
also i found that a finger belt sand is great for prep for welding

have fun and drive it like you stole it

spot

[comp]

how is it going ???